Article

Resource Partioning in Ecological Communities

August 1974
Science 185(4145):27-39

DOI:10.1126/science.185.4145.27

Source
PubMed

Authors:

University of California, Davis

To understand resource partitioning, essentially a community phenomenon, we require a holistic theory that draws upon models at the individual and population level. Yet some investigators are still content mainly to document differences between species, a procedure of only limited interest. Therefore, it may be useful to conclude with a list of questions appropriate for studies of resource partitioning, questions this article has related to the theory in a preliminary way. 1) What is the mechanism of competition? What is the relative importance of predation? Are differences likely to be caused by pressures toward reproductive isolation? 2) Are niches (utilizations) regularly spaced along a single dimension? 3) How many dimensions are important, and is there a tendency for more dimensions to be added as species number increases? 4) Is dimensional separation complementary? 5) Which dimensions are utilized, how do they rank in importance, and why? How do particular dimensions change in rank as species number increases? 6) What is the relation of dimensional separation to difference in phenotypic indicators? To what extent does the functional relation of phenotype to resource characteristics constrain partitioning? 7) What is the distance between mean position of niches, what is the niche standard deviation, and what is the ratio of the two? What is the niche shape?

Multidimensional niche partitioning allows coexistence of multiple snake species

Article

Full-text available

Feb 2025
J ZOOL

Investigations on resource use by predators are important for understanding the mechanisms of biological coexistence. Although time, habitat, and diet are considered the three major dimensions for niche partitioning, studies that comprehensively investigate these dimensions in predator guilds are limited. Snakes are one of the predators whose populations have been reported to be declining worldwide. While diet has been considered as a fundamental variable that allows snakes to coexist, the importance of spatiotemporal resources has also been noted especially in temperate regions. To clarify the coexistence mechanisms of terrestrial snakes, we assessed the niche partitioning patterns of snakes on Sado Island, a Japanese island rich in snake species, from the perspectives of spatiotemporal and dietary resources. Specifically, we investigated the daily and seasonal occurrences as temporal niches, landscape‐level distribution as a spatial niche, and stomach content as a dietary niche. We found that niche partitioning in all three major resources occurred among snake species on the island. Daily occurrence was partitioned into three groups: completely diurnal, nocturnal, and active during both periods. Seasonal occurrence was partitioned into three groups: widely active from spring to autumn, mainly active in summer, and mainly active in autumn. Distribution was partitioned into two groups: mainly distributed in lowlands and distributed even in mountainous areas. Food habits were partitioned into three groups: rodents, frogs, and earthworms as main prey, respectively. Our results provide empirical evidence that snakes can coexist through multidimensional niche partitioning, and that spatiotemporal resources are also an important force in terrestrial snake coexistence. Furthermore, we suggest that snakes on the island coexist through subtle differences along the three major niche axes, and that conservation of a variety of niches, rather than a single niche, will increase the species diversity of local snakes.

Mammalian predator co‐occurrence affected by prey and habitat more than competitor presence at multiple time scales

Article

Full-text available

Jan 2025
ECOL MONOGR

The behavior and abundance of sympatric predators can be affected by a complex dominance hierarchy. The strength of antagonistic interactions in predator communities is difficult to study and remains poorly understood for many predator assemblages. Predators directly and indirectly influence the broader ecosystem, so identifying the relative importance of competition, prey, and habitat in shaping predator interactions has broad conservation and management implications. We investigated space use among five predator species (black bear [Ursus americanus], bobcat [Lynx rufus], coyote [Canis latrans], mountain lion [Puma concolor], and gray wolf [Canis lupus]) across three temporal scales in northern Idaho, USA. We used camera trap data to test whether potentially subordinate predators spatially avoided dominant predators and how prey availability influenced those relationships. We found few instances of subordinate predators spatially avoiding dominant predators and only at the finest temporal scale of our analyses. Instead, habitat features generally influenced predator space use patterns at coarser scales whereas prey and competitor presence influenced space use patterns at finer scales. Co‐occurrence was positively associated between coyotes and bobcats at coarser timescales and between mesopredators and apex predators at finer timescales. Bobcats and mountain lions temporarily delayed the use of sites recently visited by coyotes and black bears, respectively. And all predator species used sites sooner following the detection of a competitor in areas with higher relative abundances of prey (primarily white‐tailed deer [Odocoileus virginianus]). Our results suggest attraction to shared habitats and prey resources influenced space use in the predator community more than avoidance of competitors. We propose that the effects of interspecific interactions on predator distributions were most evident for mesopredators because their trophic position requires balancing risks and rewards associated with prey, apex predators, and other mesopredators. In addition, relatively high densities of a common prey source likely facilitated the spatial coexistence in this predator community. Our study demonstrates the value of simultaneously assessing multiple interspecific interactions across different spatiotemporal scales to discern relationships within the predator guild.

Invading occupied territory? Foraging whereabouts and prey of the Caspian Gull (Larus cachinnans) colonising The Netherlands

Article

Jan 2025

Caspian Gulls (Larus cachinnans) have expanded their breeding range over around 2500 km westward, from the Black Sea to Western Europe, within decades. As a colonising species, it invaded a region with two established guild members that faced poor breeding results from declining resources. A study of breeding performance and diet of the Caspian Gulls, in combination with a tracking study to document foraging behaviour and habitat choice, meant to examine the possible occurrence of interspecific competition. The study revealed a multi-dimensional ecological separation between taxa, resulting from differences in prey choice, spatial segregation in micro- and macro-habitats plus an essential difference in seasonal timing. Caspian gulls focused on freshwater habitats, ditches and canals in agricultural areas, while avoiding offshore marine and intertidal areas, and took different prey in major areas where other taxa co-occurred. On top of that, Caspian Gulls commenced breeding a month earlier than its two sympatric guild members, such that their energetic demands peaked (during chick rearing) well before that in the established taxa. Caspian Gulls, in their early days of colonisation, have not invaded occupied territory but found an open niche.

Ecological Drivers of Molt‐Breeding Overlap, an Unusual Life‐History Strategy of Small‐Island Birds?

Article

Full-text available

Jan 2025

Terrestrial bird populations on small, species depauperate islands often experience selection for generalist foraging traits via ecological release; however, it is unclear how island conditions may uniquely influence other life‐history characteristics of small‐island birds, such as the unusually high rates of molt‐breeding overlap exhibited on the island of Grenada. To explore this question, we collected data on the life cycles and diets of 10 commonly occurring Grenadian bird species to assess the degree of generalist foraging and evaluate how seasonal patterns in diet niche breadth and diet overlap among species relates to the high rates of molt‐breeding overlap. We evaluated three hypotheses explaining drivers of molt‐breeding overlap (constraints on molt rate, unpredictable food abundance, and limited duration of food abundance), and suggest that widespread overlap in small‐island tropical communities may be the result of generalist foraging adaptations and restricted time periods of sufficient invertebrate availability for successful breeding and molt to occur. We found that these species typically exhibited low breeding period seasonality followed by synchronized peaks in molt intensity and molt‐breeding overlap during peak rainfall and high invertebrate abundance. There was also greater diet overlap and wider niche widths of invertebrate resources in the wet season when molt‐breeding overlap occurred, and greater niche partitioning of invertebrate items among species in the dry season suggesting that competitive interactions for invertebrates were stronger in the dry season. Birds also shared more plant food sources in the dry season when invertebrate abundance is low, though seasonal differences in plant diet diversity and niche width varied by species. These results provide evidence that scarce invertebrate resources and competition likely limit productivity and molt/self‐maintenance in these island‐adapted, species‐depauperate communities, and drive high rates of molt‐breeding overlap, a relatively uncommon life‐history strategy.

Translucent windows: How uncertainty in competitive interactions impacts detection of community pattern

Preprint

Full-text available

Feb 2018

Trait variation and similarity among coexisting species can provide a window into the mechanisms that maintain their coexistence. Recent theoretical explorations suggest that competitive interactions will lead to groups, or clusters, of species with similar traits. However, theoretical predictions typically assume complete knowledge of the map between competition and measured traits. These assumptions limit the plausible application of these patterns for inferring competitive interactions in nature. Here we relax these restrictions and find that the clustering pattern is robust to contributions of unknown or unobserved niche axes. However, it may not be visible unless measured traits are close proxies for niche strategies. We conclude that patterns along single niche axes may reveal properties of interspecific competition in nature, but detecting these patterns requires natural history expertise firmly tying traits to niches.

Spatiotemporal interactions facilitate sympatry in a diverse mammalian community

Article

Full-text available

Feb 2025

Understanding mechanisms underlying coexistence among potential competitors, and between predators and prey, is a persistent challenge in community ecology. Using 6 years (2013–2018) of camera‐trapping data and species interaction models, we investigated the spatiotemporal patterns of inter‐ and intra‐guild interspecific interactions in a diverse terrestrial mammalian community in Pakke Wildlife Sanctuary and Tiger Reserve (PTR), Northeast India. We found no evidence of spatial interaction among apex predators (tiger Panthera tigris, leopard Panthera pardus, and dhole Cuon alpinus). However, dholes temporally separated themselves from tigers and leopards. Among small carnivores, marbled cat (Pardofelis marmorata) and leopard cat (Prionailurus bengalensis) exhibited temporal separation, whereas leopard cat overlapped spatially and temporally with other small carnivores. Herbivores exhibited neither spatial nor temporal separation with each other. All apex predators exhibited diel activity and space‐use patterns to overlap with their preferred prey. Our results suggest that the assembly of the diverse mammalian community of PTR is a complex process, and coexistence among potential competitors, and predators and prey is likely facilitated by several mechanisms including spatial and temporal segregation, and potentially dietary separation.

Variations of egg color and oviposition site traits between two closely related spittlebugs, Callitettix versicolor (Fabricius) and Abidama liuensis (Metcalf) (Hemiptera: Cercopidae)

Article

Full-text available

Feb 2025
PEST MANAG SCI

BACKGROUND For most insect herbivores, where females decide to lay their eggs has a significant impact on offspring survival. Although females’ behavior is essential for oviposition site selection, it is unclear what role the egg itself has in this process. RESULTS Two closely related spittlebugs, Callitettix versicolor and Abidama liuensis, with diametrically opposite egg colors, were selected to investigate whether egg color has a vital role in oviposition site selection. Both spittlebugs preferred to lay eggs on the side of the substrate that had more light. Eggs laid by C. versicolor on the substrates were positioned significantly higher than eggs laid by A. liuensis. A higher position meant more light and more ultraviolet (UV) radiation. Accordingly, the different egg colors of these two spittlebugs resulted in different resistance abilities toward UV radiation. C. versicolor eggs, which are black, were more tolerant of UV radiation than the white eggs of A. liuensis. The color difference between the two spittlebugs’ eggs is caused by their melanin compositions. The UV tolerance of C. versicolor eggs allows females to occupy more space to lay eggs than A. liuensis. Consequently, the egg density of A. liuensis was higher than that of C. versicolor. CONCLUSION This study revealed that closely related species use different egg colors to segregate their eggs on the same host plant, ensuring their coexistence in the same habitat. The results also provide a behavioral and ecological basis for prevention and control strategies for these two pests. © 2025 Society of Chemical Industry.

Factors Affecting the Distribution and Temporal Patterns of a Salt Marsh Endemic Mammal

Article

Full-text available

Feb 2025
ESTUAR COAST

The salt marsh ecosystem is one of the world’s most biologically productive natural communities that integrates characteristics of both terrestrial and aquatic environments. Despite its high productivity, few terrestrial mammals have adapted to this harsh environment with its fluctuating water levels and salinity. The Gulf salt marsh mink (Neogale vison halilimnetes) is endemic to the west coast of Florida and is thought to be restricted to salt marsh. However, no formal surveys into the mink’s distribution, habitat use, activity patterns, and interactions with other mammals have occurred. From September 2014 to May 2016, we placed cameras on 513 floating platforms at 94 survey units to survey for salt marsh mammals. Using multi-species occupancy models, we studied the effects of environmental covariates and species interactions on the occupancy probability of Gulf salt marsh mink, raccoon (Procyon lotor), and marsh rice rat (Oryzomys palustris). We also used negative binomial regression to evaluate the effect of tide height and time of day on the activity of each species. We detected mink 110 times at 39 camera traps (naïve occupancy 0.08) in survey units from Homosassa to Horseshoe Beach. We detected raccoons 344 times at 104 traps (0.20), and marsh rice rats 6302 times at 357 traps (0.70) throughout the study area. We found that mink were more likely to use salt marsh closer to oyster reefs, while marsh rice rats used marsh farther from oyster reefs and major rivers. No habitat covariates were significant for raccoons. Time of day and tide height influenced activity patterns of raccoons and marsh rice rats but not the Gulf salt marsh mink. Salt marsh ecosystems are increasingly threatened by factors such as hurricane frequency, mangrove encroachment, oil spills, disease, and coastal development. These challenges, combined with the Gulf salt marsh mink detection in only a quarter of their presumed historical range, render the subspecies highly vulnerable to extirpation.

Stingray Behaviour and Habitat Use in Response to Sharks in Caribbean Coral Reef Ecosystems

Thesis

Mar 2023

Kathryn Flowers

Shark declines may cause trophic cascades, which is partially dependent on how sharks influence prey abundance and behaviour. Rays are mesopredators that play a unique role in ecosystems as bioturbators. My dissertation investigates whether sharks induce changes in ray sightings, behaviour, and habitat use across multiple spatial and temporal scales. First, I reviewed the ray ecology literature and found limited evidence for risk-induced ray trait responses (Chapter 1). Next, using a baited remote underwater video station (BRUVS) survey, I found that southern stingray (Hypanus americanus) sightings were negatively associated with shark abundance throughout the tropical Western Atlantic Ocean (Chapter 2). Other important predictors of southern stingray sightings in the region included habitat complexity, geomorphology, and bottom fishing gear. At a smaller spatial scale inside the Glover’s Reef Marine Reserve in Belize, a BRUVS survey revealed southern stingray sightings and behaviour remained stable between 2009 – 2019 despite a concurrent decline in the relative abundance of Caribbean reef sharks (Carcharhinus perezi) (Chapter 3). Habitat complexity explained southern stingray sightings and behaviour on BRUVS, which may be due to their preference for soft bottom habitats and/or because we are less likely to detect stingrays on BRUVS in areas with high reef relief. Passive acoustic telemetry showed Caribbean reef and lemon (Negaprion brevirostris) sharks use shallow lagoon habitat, which was also the preferred habitat of southern stingrays, suggesting it is unlikely a refuge from predators. Finally, using accelerometry and hidden Markov models, I found that southern stingray activity is crepuscular and nocturnal, with high individual variation (Chapter 4). Southern stingrays were highly active in shallow water (<5 m), which is likely associated with prey activity and availability. My findings emphasize the context dependent nature of predation risk effects and the need to take a multimethod approach to understand ray behaviour and habitat use.

Fantastic plants and where to find them: niche occupancyanalysis in neotropical epiphytic species

Preprint

Full-text available

Jan 2025

This new study investigates the relationship between niche occupation, phylogeny, and species distribution in the genus Microgramma (Polypodiaceae), a group of neotropical epiphytic ferns. Using species distribution modeling and niche occupation profiles, we demonstrate that broadly distributed species may exhibit different niche occupation dynamics, facilitating co-occurrence. In contrast, allopatric species, despite being geographically separated and phylogenetically distant, converge in environmental characteristics. These results provide new insights into diversification and co-occurrence processes in neotropical epiphytes.

Spatial, environmental and trophic niche partitioning by seabirds in a climate change hotspot

Article

Jan 2025
J ANIM ECOL

For similar species to co‐occur in places where resources are limited, they need to adopt strategies that partition resources to reduce competition. Our understanding of the mechanisms behind resource partitioning among sympatric marine predators is evolving, but we lack a clear understanding of how environmental change is impacting these dynamics. We investigated spatial and trophic resource partitioning among three sympatric seabirds with contrasting biological characteristics: greater crested terns Thalasseus bergii (efficient flyer, limited diver, and preference for high quality forage fish), little penguins Eudyptula minor (flightless, efficient diver, and preference for high quality forage fish) and silver gulls Chroicocephalus novaehollandiae (efficient flyer, limited diver and generalist diet). We investigated interannual variability in resource partitioning in relation to environmental variability in a climate change hotspot influenced by the warm and intensifying East Australian Current (EAC). Sampling was conducted from 2012 to 2014 during the austral summer breeding season of seabirds at Montague Island, Australia. Daily seabird movements were monitored using GPS trackers and feather tissues were collected and processed for stable isotope analysis (δ ¹⁵ N and δ ¹³ C). Generalised Linear Mixed Models were used to assess how changes in oceanographic conditions influenced space use for each species. Schoener's D and Bayesian mixing models were used to respectively investigate the levels of yearly inter‐specific environmental and trophic niche overlaps. Crested terns and little penguins were less likely to be observed in warm, saline EAC waters and crested terns and silver gulls had smaller foraging areas on days when more than 30% of available habitat was classified as EAC origin. All species preferred areas with low variability in sea surface temperature (<0.5°C). Terns and penguins occupied similar marine trophic levels, with penguins having larger isotopic niche spaces in 2014 when the EAC was more dominant in the study area. Gulls occupied the lowest trophic level, with the widest niche and lowest interannual variability in niche area. As the EAC intensifies along the southeast coast of Australia under climate change, interspecific competition for resources may increase, with the greatest impacts on species like little penguins that have relatively restricted foraging ranges. This study suggests that species‐specific biological traits and behavioural plasticity should be accounted for when predicting the effects of climate change on marine species.

The study on conservation status and behavioral adaptions on diets and activity rhythms of Myanmar or black snub-nosed monkeys (Rhinopithecus strykeri) in Pianma region, Yunnan province, China

Thesis

Full-text available

May 2024

Yixin Chen

The Myanmar or black snub-nosed monkey (Rhinopithecus strykeri) is a recently described non-human primate species. It belongs to the subfamily Colobinae and the genus Rhinopithecus. Currently, it is known to be distributed only in the Mt. Gaoligong region along the northern China-Myanmar border. Due to the harsh terrain and dense vegetation, it greatly hinders the investigation and research of this critically endangered species. Currently, very little rudimentary information of the species’ behavioral ecology, social organization, etc. is available. However, conducting behavioral ecological research on the R. strykeri is of great significance for understanding how non-human primates adapt to high-altitude environments. From January 2018 to January 2023, I carried out field survey via interview, direct tracking & observation and infra-red camera trapping to study the wild R. strykeri group in the Pianma region of Lushui City, Nujiang Lisu Autonomous Prefecture, Yunnan Province, China. This study aims to clarify population demography and conservation status of R. strykeri, as well as its behavioral ecology regarding the diet and feeding strategies, behavioral rhythms, and comparative thanatology. The findings are in the follows: 1．I led the survey team to spend a total of 504 days in the forest searching for R. strykeri, and managed to locate and follow them for a total of 75 days. Through interviews, direct field tracking & observations and infra-red camera trapping, I managed to recorded a total of 1762 geographic locations of the species. Currently, I confirmed that there was only one cross-border population of R. strykeri in the Pianma region. The multi-year home range of the group reached 51.50 – 57.02 km², and the altitude range was 2143 – 3372 m. Although the monkey group mainly ranged within China, it occasionally travelled into Myanmar. On November 18, 2020, a direct count confirmed that the monkey group is comprised of at least 149 individuals, belonging to 18 one-male, multi-female units (OMU) and two all-male units (AMU). I conservatively estimated that the actual size of the monkey group should be around 155 – 160 individuals. Through population composition analysis, it was confirmed that the monkey group had shown trends of population growth during the recent years. On the other hand, I noted that the human disturbance in the species’ habitat is generally minor, indicating that the monkey group has been currently well protected within China. However, when the monkey group travelled into Myanmar, it suffered serious threats from poaching. In the past 5 years, it was likely that 19 – 20 individuals had been killed or captured by Myanmar hunters. Mining and cross-border forest fires, particularly on the Myanmar side of the border also threatened the monkey group. To protect this cross-border population, I urged immediate transboundary collaboration to bridge the protection gaps of R. strykeri for both government authorities in China and Myanmar. 2．During the field work, I managed to record that R. strykeri consumed 314 different parts/items from at least 113 flora and fauna species. They belonged to 100 species of vascular plants from 26 families and 49 genera, eight species of lichens, three undetermined herbs and two invertebrates. The vascular plants, such as trees and shrubs from Araliaceae, Fagaceae, Magnoliaceae, Lauraceae, Rosaceae and Rutaceae were the bulk of diets for the species. R. strykeri exhibited seasonal preference on their diets and food choices. Generally, they preferred to eat highly seasonal food parts/items. For examples, in spring, they significantly prefer to eat buds, young leaves, twigs and flowers. In summer, they prefer to eat bamboo shoots, while in autumn and winter, they significantly prefer to eat fruits/seeds. The feeding strategy of R. strykeri conformed to the prediction of the optimal feeding theory. With the seasonal changes of phenology and food availabilities, R. strykeri optimized the energy and nutrition intakes by concentrating on eating a large amount of high-quality, seasonal food parts/items whenever available. On the contrast, when such high-quality seasonal foods were relatively scarce, R. strykeri appropriately consumed more fall-back foods, such as mature leaves, lichens, and barks to ensure necessary energy intakes. However, given the food resources were generally abundant throughout the year, the amount of consumed fall-back foods was relatively low. 3．The study quantified the time budget pattern and daily activity rhythm of the wild R. strykeri population. The monkey group adopted a “high-risk, high-reward” strategy in the time budget pattern. Although there were seasonal differences, R. strykeri would have a higher proportion of moving behavior in all seasons of the year, implying that the monkey group needed to actively search for food to cope with the scattered distributions of preferred food resources in the mountain forest of Mt. Gaoligong. In addition, this study also found that the activity levels and patterns of the monkeys’ moving, feeding, resting, and social behaviors generally showed significant seasonal differences. Such as the activity levels of moving, feeding and social activities were generally higher in spring and autumn when high-quality, seasonal foods were generally more abundant. The activity levels of the most behaviors in summer and winter were relatively low, and the peaks of activity patterns of R. strykeri were generally delayed. The peak of feeding behavior during the morning in colder seasons (such as winter, spring or dry season) shifted earlier and R. strykeri exhibited a trend of intensifying on feeding; The resting behavior near the morning (06:00) and evening stages (18:00) implied that the individuals of the monkey group tried to extend the resting time at the night sleeping sites to save energy expenditure. These findings implied that R. strykeri adjusting its time budget pattern and daily activity rhythm in response to seasonal variations of food resources, temperature and precipitation. It was a reasonable behavioral strategy to maximize fitness gained by balancing cost-benefit on time and energy for the species. 4．The study also recorded the first thanatological events of the R. strykeri in the wild. The group members occasionally returned to the location of their deceased conspecific and exhibited behavior including looking down at the carcass, making alarm and mournful contact calls, hugging social partners and repelling individuals from other social units. It suggested strong social bonds and emotions/cognitions related to the death of OMU member in R. strykeri group. The infra-red camera trapping showed that Siberian weasel (Mustela sibirica) was the principal scavenger feeding on the R. strykeri carcass, while the yellow-throated marten (Martes flavigula) also participated in scavenging. Siberian weasels maximized net energy and nutrition gains by significantly increasing activity levels and time spent feeding on the R. strykeri carcass when carrion availability was high while maintaining vigilance in response to potential competitors and predators. After the R. strykeri carcass was largely consumed and decayed, the frequency and duration of feeding and vigilance behaviors decreased. However, Siberian weasels constantly inspected the R. strykeri carcass throughout the entire decay process regardless of the change in carrion availability. It suggested that Siberian weasels adopted dynamic behavioral strategies while scavenging in response to changes on carrion availability, competition avoidance and predation risk. In sum, by conducting comprehensive surveys, this study offered the latest and detailed information regarding the distribution, population demography and conservation status of the cross-border group of R. strykeri in the Pianma region. I managed to explore the behavioral adaptation mechanisms of the monkey group to the mid-high altitude mountain forests in terms of diet, feeding strategy, daily activity rhythm and time budget strategy. I also reported thanatological events of R. strykeri, and the behavior strategy of scavengers feeding on its carcass. The information greatly enriched the rudimentary information of conservation biology and behavioral ecology of the critically endangered R. strykeri. It was significantly important for promoting accurate conservation on this species, and enriched the understanding of the adaptation mechanism of non-human primates to mid-high altitude mountain forests.

Gut microbiota profiles of sympatric snub-nosed monkeys and macaques in Qinghai-Tibetan Plateau show influence of phylogeny over diet

Article

Full-text available

Jan 2025

The unique environment of the Qinghai-Tibetan Plateau provides a great opportunity to study how primate intestinal microorganisms adapt to ecosystems. The 16S rRNA gene amplicon and metagenome analysis were conducted to investigate the correlation between gut microbiota in primates and other sympatric animal species living between 3600 and 4500 m asl. Results showed that within the same geographical environment, Macaca mulatta and Rhinopithecus bieti exhibited a gut microbiome composition similar to that of Tibetan people, influenced by genetic evolution of host, while significantly differing from other distantly related animals. The gut microbiota of plateau species has developed similar strategies to facilitate their hosts’ adaptation to specific environments, including broadening its dietary niche and enhancing energy absorption. These findings will enhance our comprehension of the significance of primate gut microbiota in adapting to specific habitats.

Morphological differences between wild and game‐farm Mallards ( Anas platyrhynchos ) in North America

Article

Full-text available

Jan 2025
IBIS

Large‐scale releases of domesticated, game‐farm Mallards Anas platyrhynchos to supplement wild populations have resulted in widespread introgressive hybridization that changed the genetic constitution of wild populations in eastern North America. The resulting gene flow is well documented between game‐farm and wild Mallards, but the mechanistic consequences from such interactions remain unknown in North America. We provide the first study to characterize and investigate potential differences in morphology between genetically known, wild and game‐farm Mallards in North America. We used nine morphological measurements to discriminate between wild and game‐farm Mallards with 96% accuracy. Compared with their wild counterparts, game‐farm Mallards had longer bodies and tarsi, shorter heads and wings, and shorter, wider and taller bills. The nail on the end of the bill of game‐farm Mallards was longer, and game‐farm Mallard bills had a greater lamellae:bill length ratio than wild Mallards. Differences in body morphologies between wild and game‐farm Mallards are consistent with an artificial, terrestrial life whereby game‐farm Mallards are fed pelleted foods, resulting in artificial selection for a more ‘goose‐like’ bill. We posit that: (1) game‐farm Mallards have diverged from their wild ancestral traits of flying and filter feeding towards becoming optimized to run and peck for food; (2) game‐farm morphological traits optimized over the last 400 years in domestic environments are likely to be maladaptive in the wild; and (3) the introgression of such traits into wild populations is likely to reduce fitness. Understanding the effects of game‐farm Mallard introgression requires analysis of various game‐farm × wild hybrid generations to determine how domestically derived traits persist or diminish with each generation.

Table for two: Diet composition differences of allopatric and sympatric populations of island geckos

Article

Full-text available

Jan 2025

Oceanic islands are exciting models for studying how evolutionary processes and environmental variables can jointly contribute to speciation and community assembly over time. In this context, the Cabo Verde archipelago serves as a simplified natural laboratory, harbouring a group of endemic reptile species that are descended from a single common ancestor, with sympatric species exhibiting wide morphological variation, particularly for size, and competing for limited food resources. This framework allows for the exploration of how the diet composition of closely related and spatially overlapping species is influenced by competition. This is exemplified by the two endemic wall geckos, Tarentola gigas and Tarentola raziana, which occur in sympatry on Raso Islet, with the latter also occurring in allopatry on Santa Luzia Island, due to the human-mediated extinction of T. gigas. DNA metabarcoding of faecal pellets was used to compare the diets of both sympatric and allopatric populations. It revealed significant differences in diet composition between both populations of T. raziana, with significantly lower prey richness and niche breadth in the Santa Luzia population. Differences observed in sympatric species were due to a higher incidence of vertebrates and plants in the diet of T. gigas, while differences between the allopatric populations of T. raziana were due to a higher incidence of plants and a lower incidence of invertebrates in the population of Santa Luzia, compared to Raso. These results suggest that competition has played an important role in structuring the stable coexistence of these species in sympatry, promoting extreme morphological discrepancies that allowed resource partitioning. In addition, this study reveals unexpected dietary differences within the allopatric population of T. raziana on Santa Luzia, suggesting a niche shift in response to the absence of a direct competitor that may influence the reintroduction planning of T. gigas. Hence, this work highlights the importance of understanding the mechanisms of resource partitioning for conservation efforts and management, especially for fragile island ecosystems.

The Spatial Relationship Between Two Sympatric Pheasant Species and Various Human Disturbance Activities

Article

Full-text available

Jan 2025

Establishing and managing nature reserves to mitigate wildlife habitat loss and fragmentation is challenging, particularly in the face of increasing human activity. To understand how wildlife coexists in environments affected by anthropogenic disturbances, we conducted a 19-month survey examining the Reeves’s pheasant (Syrmaticus reevesii) and Koklass pheasant (Pucrasia macrolopha) in the Anhui Tianma National Nature Reserve, China. Previous studies of large terrestrial birds focused primarily on livestock impacts, with less attention given to other human activities. We used occupancy models and performed daytime activity rhythm analysis based on camera trap data to examine the spatiotemporal responses of these species to human activities, livestock, and domestic dogs. The results showed that human disturbance activities within the reserve impact the distribution patterns of Reeves’s pheasant and Koklass pheasant, but the effect was not significant. In high-disturbance environments, both species adjusted their activity times to avoid direct or indirect interactions with humans, livestock, and dogs. These findings provide insights for replanning core and creation of buffer zones within the reserve and have broader implications for conservation strategies in similar habitats. Our study suggests that well-designed conservation objectives can balance species protection with sustainable human presence.

Associations between patterns of wild ungulate patch use, soil carbon and albedo in montane grasslands

Thesis

Full-text available

Dec 2024

Steven McGregor

Grassy ecosystems are essential for human survival, providing key services including food production, water provisioning and moderating climate. Yet, grassy ecosystems remain undervalued due to misconceptions that they are remnants of degraded states of forest – a view that continues to influence climate change policies. This thesis explores the links between wild, free-roaming ungulate grazers and climate drivers, including carbon storage and surface albedo (i.e., reflectance of solar radiation), through their impacts on vegetation and soils. Using black wildebeest (Connochaetes gnou) as a model wild species, I compared their grazing patterns in an Afromontane grassland in the eastern Karoo, South Africa, to those of short-duration cattle grazing systems in similar nearby grasslands (Chapter 2). While short-duration grazing aims to mimic spatiotemporal wild ungulate grazing patterns to supposedly enhance ecosystem functioning and soil carbon stocks, I found that wildebeest had ~50% shorter grazing durations and much shorter rest intervals (1-5 days versus 60-365 days), revealing key differences in grazing patterns that may affect vegetation and climate feedbacks. Next, I examined spatial variations in soil organic carbon (SOC) stocks between grass growth forms that differ in grazing tolerance (Chapter 3). Red grass (Themeda triandra) tussock patches, sensitive to frequent grazing, had higher SOC to a soil depth of 20 cm (61.45 ± 1.59 Mg C·ha-1) than intensively grazed, prostrate-growing Cynodon dactylon grazing lawns (55.43 ± 3.40 Mg C·ha-1), likely due to greater shading and soil moisture beneath tussocks which drives microbial decomposition. Seasonal albedo variations were then assessed across distinct grassland patch types among seasons to determine whether albedo varies seasonally at fine patch-scales between grass patches, between shrub and grass patches, and with grazing (Chapter 4). Albedo was lower during the growing season compared to dormancy, and was consistently lower in dwarf shrub (Pentzia incana) encroached patches compared to grass patches. No albedo differences between grazed and less-grazed tussock grass patches of the same species were found, although intensively grazed grazing lawns had consistently higher albedo than most patch types. Finally, I evaluated trade-offs between plant carbon, albedo, and their impacts on radiative forcing (i.e., atmospheric warming/cooling) resulting from patch type changes commonly found in grassy ecosystems (Chapter 5). The loss of perennial grass cover resulted in the highest net positive (warming) effect, mostly due to reduced root biomass. Additionally, shrub encroachment into all patches lowered albedo, but led to negative (cooling) effects from shrub encroachment into bare ground patches due to biomass gains. This thesis challenges current views of grassy landscapes and short-duration grazing systems, emphasizing the need to rethink climate change mitigation strategies to prioritize maintaining heterogeneity, while enhancing carbon sequestration and albedo in grassy ecosystems.

The influence of environmental factors on the encounter rate of two diurnal stream-dwelling frogs of the Atlantic Forest

Article

Full-text available

Mar 2025
J NAT HIST

Abiotic factors, such as available microhabitats, water volume, and elevation, influence stream-dwelling frog abundance and/or detect-ability. These factors can differently affect frog abundance according to specific conditions favouring reproduction and tadpole development. Frogs endemic to streams in the Atlantic Forest biome, such as diurnal forest specialists in the genera Crossodactylus and Hylodes (Hylodidae), frequently occur in Reserva Ecológica de Guapiaçu in southeastern Brazil. Here, we analysed the microhabitat use and influence of environmental factors on the encounter rate (number of individuals found in transects) of two sympatric and syntopic hylodids, C. gaudichaudii and H. pipilans. Hylodes pipilans was more frequently encountered, and occurred in a greater number of streams, compared to C. gaudichaudii. Most individuals of C. gaudichaudii utilised leaf litter, while H. pipilans predominantly used rocks. For C. gaudichaudii, increasing mean stream width and proportion of sandy substrate was associated with higher encounter rates, while increasing altitude and proportion of rocky substrate were associated with low encounter rates. For H. pipilans, we detected a positive effect of altitude and the proportion of rocky substrate in the streams on encounter rates. Thus, each species utilised microhabitat categories in distinct ways, and environmental factors had different effects on their encounter rates. Protecting stream-dwelling frogs in the Atlantic Forest may require preserving different types of lotic microhabitats.

Home Is Where the Newts Are: Suitability of Artificial Aquatic Sites for the Italian Crested Newt in a Traditional Farming Landscape in Central Italy

Article

Full-text available

Mar 2025
ANIM CONSERV

In Mediterranean farming landscapes, natural waters are declining, leading to serious consequences for amphibians. In this context, artificial water bodies, used for livestock supply, may represent an ecological surrogate for natural ones. Here, we investigated the habitat suitability of natural and artificial aquatic sites for Triturus carnifex within a farming area where traditional practices are declining. The main goal was to clarify if artificial sites represent keystone habitats contributing to amphibian persistence. Site suitability was assessed by a Habitat Suitability Index (HSI), a body condition index (BCI) and evaluating newt trophic strategy in terms of diet composition and individual specialization (V). HSI was similar in artificial and natural waters, with most study sites falling into the “Good”‐“Average” categories. Drinking troughs seem to fulfill the ecological requirements of the species with a habitat suitability that can be improved by a proper management. BCI did not vary between artificial and natural sites, suggesting that newts were well locally adapted, exploited resources with similar energetic cost‐efficiency, and experienced similar predation and competition. Diet composition varied between artificial and natural sites because of the opportunistic feeding behavior of T. carnifex, the specialization towards different prey, and site‐specific environmental conditions. Individual specialization was significant in artificial and natural sites, confirming the availability of resources in drinking troughs. Indeed, V is more frequent in environments where prey is highly available and profitable to hunt. Our findings suggest that artificial sites with specific habitat suitability sustain specialized individuals with good body conditions. If properly managed, they may support newt vital activities, especially feeding, representing an ecological surrogate for natural sites. In the face of freshwater loss, they represent an opportunity to preserve amphibians in farming landscapes. The recognition of their conservation value is timely, given the spread of intensive farming and the threatened status of many amphibians.

Can Fish Escape the Evolutionary Trap Induced by Microplastics?

Article

Full-text available

Mar 2025
ENVIRON SCI TECHNOL

Niche partitioning between two marsupials inhabiting the Yungas of Northwestern Agentina: overlapping diets in non-overlapping lifestyles?

Article

Feb 2025
MAMMALIA

Marmosa rapposa and Thylamys sponsorius were captured in syntopy in the locality of Isla de Cañas Salta province, Argentina. We studied the stomach contents of 7 M. rapposa and 10 T. sponsorius and identified arthropods and plant material as the main items. Niche overlap was studied using the Pianka index. We found that arthropods were the most abundant items in both species (67 % in M. rapposa, 63.5 % in T. sponsorius), and plant material represented 29.6 % and 35.5 %, respectively. Insects were the main item in both species (45 % in M. rapposa, 58.5 % in T. sponsorius), while spiders were more abundant in the diet of M. rapposa (21.7 % vs. 5 % in T. sponsorius). The dietary overlap between the two species was high (91.1 %); a similar result was found between males and females of M. rapposa (74.2 %) and T. sponsorius (77.4 %). Non-parametric analyses using PERMANOVA and Principal Coordinate Analysis showed the same pattern, with broad overlap in the diets of the species. The coexistence of these two species may be due to temporal segregation (which we could not study) or different habitat use (more prominent palmar and plantar calluses in M. rapposa indicate a more arboreal lifestyle than that of T. sponsorius).

Emergence of ecological structure and species rarity from fluctuating metabolic strategies

Preprint

Full-text available

Feb 2025

Ecosystems often demonstrate the coexistence of numerous species competing for limited resources, with pronounced rarity and abundance patterns. A potential driver of such coexistence is environmental fluctuations that favor different species over time. However, how to include and treat such temporal variability in existing consumer-resource models is still an open problem. In this study, we examine the role of correlated temporal fluctuations in metabolic strategies within a stochastic consumer-resource framework, reflecting change of species behavior in response to the environment. In some conditions, we are able to solve analytically the species abundance distributions, through path integral formalism. Our results reveal that stochastic dynamic metabolic strategies induce community structures that align more closely with empirical ecological observations and contribute to the violation of the Competitive Exclusion Principle (CEP). The degree of CEP violation is maximized under intermediate competition strength, leading to an intermediate competition hypothesis. Furthermore, when non-neutral effects are present, maximal biodiversity is achieved for intermediate values of the amplitude of fluctuations. This work not only challenges traditional ecological paradigms, but also establishes a robust theoretical framework for exploring how temporal dynamics and stochasticity drive biodiversity and community.

Acoustic ecology of anuran communities across Andean biomes: unveiling the soundscape of Northeastern Colombia

Article

Feb 2025
BIOACOUSTICS

Vocalisation acts as a primary communication mechanism in anurans, enabling the transmission of information between individuals in a community, facilitating mutual recognition, territorial dispute resolution, mate selection, and prevention of hybridisation. The interaction between habitat characteristics and species composition plays a significant role in shaping the acoustic structure of anuran communities. This study aims to characterise the advertisement calls of anuran species distributed in the Pamplonita River Basin, northeastern Colombia, and to examine how competition and habitat features affect their acoustic structure. It is proposed that environmental selection pressures, as outlined by the Acoustic Adaptation Hypothesis (AAH), and acoustic competition, as described by the Acoustic Niche Hypothesis (ANH), both influence the acoustic structure of communities. Descriptive and multivariate statistical analyses were employed to characterise the calls of species from five representative Andean biome localities, evaluating both hypotheses. A total of 23 species, representing 6 families and 13 genera, were recorded and described, including three candidate species and first-time descriptions for five species. The analyses revealed a clear separation among species based on their call characteristics, supporting the ANH. Furthermore, species’ vocalisations varied according to the specific environmental conditions of each habitat, lending support to the AAH.

Effect of drought disturbance in a sclerophyll forest on the micromammal community in the Río Clarillo National Park, Metropolitan Region, Chile

Article

Full-text available

Jan 2025
REV CHIL HIST NAT

Background Micromammals play an important role in mediterranean ecosystems. The “megadrought” in the sclerophyll forest has caused a “browning” that implies, among other things, the reduction of canopy cover. The effects of forest browning on the taxonomic and functional diversity of micromammals were evaluated. Methods Forests with high and low disturbance degree were characterized based on the level of browning and canopy cover. To study the community of micromammals in these forests, the Capture-Mark-Recapture method was used with Sherman traps. Community indices such as Shannon–Wiener and Pielou were calculated. The Coefficient of Variation was used to study functional diversity for each trait separately. Multivariate measures FRic, FEve and FDiv were used to determine multidimensional diversity. Results We observed differences in species composition and in richness, diversity, and cover variables between forest types. However, micromammal communities were similar in taxonomic and functional diversity in highly and slightly disturbed forests. Discussion The micromammal community appears to show some resistance to forest changes due to disturbance, which could be related to their generalist diet and high dispersal capacity. The presence of the genus Rattus could entail a decrease in native rodent diversity and could have a greater effect than the disturbance of the forest due to drought. These results are an invitation to conduct long-term studies to better understand the potential vulnerability of the different micromammal species to disturbed sclerophyll forests affected by drought.

Convergent decoupling of individual specialization and niche width during ecological release

Article

Full-text available

Jan 2025
OECOLOGIA

Trophic niche has fundamental ecological importance, but many studies consider few niche metrics and most neglect critical structuring processes. Multiple processes shape trophic niches, including inter and intra-specific competition, predation and resource diversity. These processes interact and effects vary with time and taxa. The White Sands dunefield provides an ecological gradient ideal for understanding variation in niches. We measured population niche width, trophic position and individual specialization in four lizard species across habitats over 2 years. The habitats include White Sands interior, the surrounding desert scrub, and their ecotone. We used arthropod, lizard and plant stable isotopes to quantify niches. We sampled lizard competitors, predators and prey as proxies for ecological processes. We found substantial variation in niches across populations but convergence between species. Individual specialization and population niche width were surprisingly decoupled. Specialization was highest in habitats with low species diversity (White Sands) and population niche width highest at intermediate diversity (ecotone). White Sands lizards may exhibit ‘ultra partitioning’; high specialization alongside low individual niche widths. Population niche width is likely constrained within White Sands by low prey diversity. High ecotonal population niche widths may be due to fewer natural enemies than desert scrub but higher resource diversity than White Sands. Trophic position and specialization were positively correlated, suggesting stronger intraspecific competition at higher trophic levels. Prey diversity, inter and intra-specific competition, and predation all interacted to shape niches. Our results highlight the need for measuring multiple components of community structure and niches, as results are likely misleading in isolation.

Low Abundance of Regular Pollinators and Indirect Competitive Effects of Dominant Small Bees Negatively Affect Passion Fruit Pollination in Smallholder Croplands

Article

Full-text available

Jan 2025
NEOTROP ENTOMOL

Land-use changes have led to natural habitat loss and fragmentation, favoring the occurrence of dominant bee species in agroecosystems. This has raised concerns on the dominance effects in pollination-dependent crops like passion fruits (Pas-siflora edulis Sims) in tropical regions. That is because dominant bee species might overlap their foraging time with regular pollinators, potentially impairing crop yield. Our aim was to understand how dominant small bees affect regular pollina-tors of passion fruit flowers and its implications on crop production for smallholder farmers. We sampled bees on farms cropping yellow passion fruits in the Cerrado, the Brazilian savanna, and established pollination exclusion experiments to evaluate the interacting effects of dominance and bee community composition on crop yield. We observed a low frequency of regular pollinators, while dominant floral visitors were highly abundant. Dominant pollinators highly overlapped their foraging activity with regular pollinators through time. Contrary to our expectations, the dominance of native and non-native bee species did not directly affect the occurrence of regular pollinators nor crop yield. However, we found evidence that exploitative competition may indirectly affect pollination by regular pollinators. Manual and bee pollination combined increased fruit quality, highlighting the potential benefits of diverse pollinator communities for sustainable crop production. Our findings emphasize the need for strategies that can improve the quality and abundance of resources in agroecosystems for regular native pollinators to optimize pollination in passion fruits on smallholder farms and reduce dominance effects caused by small floral-visiting bees.

Spatial and Temporal Relationships Between Roe and Red Deer in an Alpine Area

Article

Full-text available

Jan 2025

Interspecific interactions are important drivers of population dynamics and species distribution. These relationships can increase niche partitioning between sympatric species, which can differentiate space and time use or modify their feeding strategies. Roe deer Capreolus capreolus and red deer Cervus elaphus are two of the most widespread ungulate species in Europe and show spatial and dietary overlap. However, limited information is available on their interspecific relationships, especially in mountainous areas. In this study we used 5 years of camera trapping data collected in the Stelvio National Park (Central Italian Alps) to investigate spatial and temporal interactions between roe deer and red deer. Analyses were based on 2060 and 9030 roe deer and red deer detections, respectively, collected from July to September, from 2019 to 2023, using 50 camera traps randomly distributed over a 10,000‐ha study area. Spatial interactions were assessed by fitting a single‐season, single‐species occupancy model to calculate the probability of roe deer detection and occupancy as a function of relative red deer abundance and site‐specific environmental covariates. Temporal interactions were obtained by comparing the diel activity patterns of the two species. Results showed no significant effect of red deer relative abundance on the probability of presence of roe deer. Spatial analysis suggested a higher probability of roe deer presence in forested habitats, at lower elevations, and in areas with gentler slopes. Diel activity patterns of roe deer were consistent across sites with higher and lower red deer relative abundance, with moderate to high interspecific overlap, suggesting moderate temporal partitioning and no major support for temporal avoidance of the latter by the former. The high degree of overlap between the two species may be the result of area‐specific ecological conditions, such as the widespread distribution of red deer during the summer period, as well as of the adoption of strategies that favor coexistence.

Study of the presence of pollen grains in the body of nocturnal bees in a deciduous forest area in Bahia, Brazil

Article

Jan 2025
J APICULT RES

Sky High or Grounded: Nest Site Selection of Herons and Egrets in a Mixed‐Species Colony

Article

Full-text available

Jan 2025

Resource partitioning is crucial for the coexistence of colonial herons, as it allows multiple species to share the same habitat while minimising competition. This study took advantage of a natural experiment in 2006 and 2007 when Black‐crowned Night Herons were prevented from breeding at Lake Fetzara in the first year due to the presence of a feral cat. This event provided valuable insight into the spatial and temporal dynamics of nest site selection among coexisting heron species, which consisted of Cattle Egrets (Ardea ibis), Little Egrets (Egretta garzetta) and Squacco Herons (Ardeola ralloides). After the cat was removed, egg‐laying began in the core areas of the colony and gradually spread to the periphery. Species that initiated nesting early selected mid‐elevation sites near the tree trunk, which likely offered protection from both ground and aerial predators, while also providing some shielding from solar radiation and strong winds. These early selected sites featured larger branches, which conferred greater nest stability. Vertical stratification was evident among the heron species; however, contrary to long‐standing assumptions, it was not directly related to body size. Both vertical and horizontal stratification were observed, with nests progressively moving higher and further from the tree trunk as the breeding season advanced. The following year, Black‐crowned Night Herons displaced other species to lower heights and positions further from the trunk, highlighting the significant influence of interspecific interactions on nest site selection. This study underscores the complex interplay between nest site selection, biotic interactions and abiotic factors in heron colonies, emphasising the importance of resource partitioning in maintaining species coexistence in densely populated breeding sites.

Formation of Adaptive Trophic Niches of Euryphagous Fish Species in Response to Off-Seasonal Water Level Regulation in Hongze Lake

Article

Full-text available

Dec 2024

Off-seasonal water level regulations disrupt the biological traits and phenological rhythms of native fish species, yet their impacts on interspecific trophic interactions remain understudied. This study employed stable isotope analysis to assess the trophic dynamics of three fish species (Parabramis pekinensis, Carassius auratus, and Toxabramis swinhonis) across different water periods in Hongze Lake. The findings revealed that all three species occupied similar mid-level trophic positions, with no significant difference among water periods (p > 0.05). During high-water periods, P. pekinensis and T. swinhonis exploited broader niches, while C. auratus relied on a narrower diet. In contrast, during low-water periods, C. auratus expanded its niche, while P. pekinensis and T. swinhonis reduced their isotopic niche widths. Niche overlap analysis showed minimal trophic overlap among the three species during high-water periods, with increased overlap during low-water periods, except for the highest overlap between C. auratus and T. swinhonis during mid-water periods. This variation in niche overlap aligns with shifts in dietary reliance, as POM was the predominant dietary component for all three species, but its contribution varied significantly across different water periods. These findings indicated that adaptive trophic niche facilitated the coexistence of these fish species, while off-seasonal water level regulation may intensify interspecific competition. These insights are essential for refining water management policies and developing sustainable fishery management strategies of Hongze Lake and other water-level-regulated systems.

Field Notes: Understanding the Habitat Range and Density of Two Endemic Partridges in Mount Kinabalu, Malaysian Borneo

Article

Full-text available

Dec 2024

The Crimson-headed Partridge and the Red-breasted Partridge are endemic to Borneo and the only members of the Phasianidae family found in the montane forests of Mount Kinabalu. Despite their ecological significance, their populations are declining due to habitat loss, forest degradation, and hunting. This study, conducted from 2014 to 2015, aimed to estimate their densities along an altitudinal gradient, analyse their activity patterns, and investigate habitat use. Bird detections were recorded through direct sightings and call counts using quiet walking surveys along six transects at varying elevations. Both species were observed between 1500 and 1900 m a.s.l., with no detections in lower elevations (600–1000 m a.s.l.). The highest mean detection for the Crimson-headed Partridge was recorded in montane forests (1500–1720 m a.s.l.) at 9.50 ± 2.89 individuals per visit/km², while the Red-breasted Partridge was most abundant in upper montane forests (1800–1900 m a.s.l.), with 3.14 ± 2.34 individuals per visit/km². Both species exhibited the lowest detections above 1900 m a.s.l. Activity patterns revealed that both species were vocal throughout the day (83% of a 10-hour monitoring period), with peak calling occurring between 0700 and 0900 hours. The Crimson-headed Partridge’s activity was predominantly concentrated between 1500 and 1700 m a.s.l., while the Red-breasted Partridge preferred higher elevations. Despite sharing similar feeding and roosting grounds, no evidence of competition for resources was observed, likely due to the abundance of suitable habitats provided by Kinabalu Park’s pristine forests. However, threats outside the park’s boundaries, such as logging and hunting, pose significant risks to their populations. This study underscores the importance of conserving montane forests and highlights the need for future research to understand the ecological and behavioral adaptations of these species, particularly in response to environmental changes and habitat degradation.

Size and Prey of Four Sympatric Felids of Southeast Asia: Trophic Niche Partitioning of Carnivores in Tropical Forests

Thesis

Full-text available

Mar 2023

Seng Yian Chew

Southeast Asia has among the highest diversity of Felidae globally, with up to eight sympatric species on parts of the continent. However the ecology of felids other than the tiger and leopard is poorly known, leading to a lack of knowledge on interspecies competition and co-existence. Intraguild size differentiation is a common phenomenon in animals, as a way of niche partitioning with respect to food resources. While physical traits such as skull morphology have been analyzed extensively in felids, little attempt has been made to associate the differences with ecological niche separation. Here I review the diets of tiger, leopard, clouded leopard, and Asian golden cat in continental Southeast Asia, calculating mean prey size and pair-wise trophic overlap. This is compared to measurements of cranial dimensions, with the aim of investigating size differences in relation to niche overlap. Divergence in average cranial size between the four species was observed, with upper jaw width showing least overlap. The proportionately longer canines of clouded leopard clearly separated it from the other three felids. Mean prey size increased with increase in mean jaw width, with a noticeable shift in diet towards medium and larger prey for leopard and tiger. Trophic overlap between each felid species was higher with decreasing difference in size, implying greater intensity of competition. The similarity in trophic niche between leopard and the other three species, especially with clouded leopard may have contributed to its local extirpation from Laos and other parts of Southeast Asia. Maintenance of prey species variety and abundance is therefore crucial to sustain the diversity and populations of wild felids by ensuring sufficiency of preferred food type for co-existing predator species.

Metabarcoding Reveals Meiofaunal Diversity in Rhodolith Beds From SE Brazil

Article

Dec 2024
AQUAT CONSERV

Rhodolith beds (RBs) are known to increase the seabed complexity and act as a hotspot, supporting a unique biodiversity. This increased structural complexity due to the presence of rhodolith nodules is expected to influence benthic diversity at a local scale. To investigate this further, we tested the hypothesis that high-density rhodolith beds hold higher meiofaunal diversity than low-density beds. We used metabarcoding (V9 hypervariable region from 18S SSU rRNA) on sediment samples from a region with extensive rhodolith beds in the Eastern Brazil Marine Ecoregion, with distinct areas covered by high-and low-density beds. The sediment underneath high-density beds showed higher food availability (biopolymeric carbon) and organic matter quality (pro-tein content and protein-to-carbohydrate ratio); however, meiofaunal composition and phylogenetic diversity was similar among all rhodolith beds sampled in the study area. Shannon's diversity was lower in high-density beds, which may be attributed to the higher organic matter content and quality supporting strong competitors, such as crustaceans and annelids that may dominate and suppress the presence of other meiofaunal taxa. Our results showed that rhodolith beds host a number of meiofaunal zoo-benthos that are rarely sampled with traditional morphology-based methods, and we suggest that metabarcoding may become an important complementary method to study rhodolith beds globally. As assessing biodiversity is a prerequisite for any conservation measures, this study can provide insights when managing valuable marine habitats.

Who's the boss? Understanding the spatial relationship between snow leopard and Eurasian lynx in southern Mongolia

Article

Full-text available

Dec 2024

Interspecific competition, a fundamental ecological process characterized by negative interactions between species, plays a vital role in shaping ecological communities. Despite the co‐occurrence of the snow leopard Panthera uncia and the Eurasian lynx Lynx lynx across vast landscapes in Asia, their interactions remain poorly understood. In this study, we investigated how the presence of snow leopards affected site‐use by lynx and whether the presence of snow leopards resulted in behavioral adaptations by the lynx. Between 2017 and 2022, we conducted camera trap‐based surveys across six sites in southern Mongolia and evaluated species co‐occurrence by snow leopards and lynx using the occupancy framework. We assumed snow leopards to be the dominant species while using topographical and land cover variables as covariates. Our results show that the presence of snow leopards influenced site‐use by lynx, leading to a shift in space use when snow leopards were present. Specifically, lynx used the entire range of ruggedness and did not select for shrubby areas in the absence of snow leopards, whereas they avoided rugged areas and had a strong preference for shrubby areas when snow leopards were present. Our findings emphasize the influence a larger predator can have on the space use of a smaller predator, and how the presence of snow leopards can alter the space‐use of lynx. Understanding these interactions and behavioral adaptations can be useful for developing effective conservation strategies in the region.

Stochastic competitive exclusion leads to a cascade of species extinctions

Preprint

Aug 2016

Community ecology has traditionally relied on the competitive exclusion principle, a piece of common wisdom in conceptual frameworks developed to describe species assemblages. Key concepts in community ecology, such as limiting similarity and niche partitioning, are based on competitive exclusion. However, this classical paradigm in ecology relies on implications derived from simple, deterministic models. Here we show how the predictions of a symmetric, deterministic model about the way extinctions proceed can be utterly different from the results derived from the same model when ecological drift (demographic stochasticity) is explicitly considered. Using analytical approximations to the steady-state conditional probabilities for assemblages with two and three species, we demonstrate that stochastic competitive exclusion leads to a cascade of extinctions, whereas the symmetric, deterministic model predicts a multiple collapse of species. To test the robustness of our results, we have studied the effect of environmental stochasticity and relaxed the species symmetry assumption. Our conclusions highlight the crucial role of stochasticity when deriving reliable theoretical predictions for species community assembly.

Trophic niche variation driven by water level fluctuations facilitates the co‐occurrence of invasive tilapia species in a subtropical reservoir in China

Article

Full-text available

Dec 2024
J FISH BIOL

Investigating how multiple invasive fish species with similar ecological traits respond to different environmental conditions is crucial to understanding their successful invasion and coexistence. Here, we used stomach content analysis and stable isotope analysis to analyse the effects of water level fluctuation on the trophic niche plasticity of three dominant co‐occurring invasive tilapia species (Coptodon zillii, Sarotherodon galilaeus, and Oreochromis niloticus) in the Shanmei Reservoir, southern China. We found that the tilapia species exhibited an iliophagous habit with dietary variations between the high‐water (HW) and low‐water (LW) level periods. During the LW period, tilapia fishes primarily fed on periphytic algae, whereas during the HW period, they reduced their consumption of epiphytic algae and increased their intake of plant remains. Biofilms were the most assimilated resource by the species during the LW period, whereas riparian plants dominated during the HW period. The niche width and niche overlap of the three tilapia species were significantly greater in the HW period than in the LW period. However, their trophic positions were not significantly affected by water level fluctuations. Our findings indicate that temporal variation in diet composition and trophic niche, driven by water level fluctuations, may favor food resource partitioning and facilitate the coexistence of these invasive tilapia species.

The roles of isolation and interspecific interaction in generating the functional diversity of an insular mammal radiation

Article

Dec 2024
OIKOS

Communities that occupy similar environments but vary in the richness of closely related species can illuminate how functional variation and species richness interact to fill ecological space in the absence of abiotic filtering, though this has yet to be explored on an oceanic island where the processes of community assembly may differ from continental settings. In discrete montane communities on the island of Sulawesi, local murine rodent (rats and mice) richness ranges from 7 to 23 species. We measured 17 morphological, ecological, and isotopic traits – both individually and as five multivariate traits – in 40 species to test for the expansion or packing of functional space among nine murine communities. We employed a novel probabilistic approach for integrating intraspecific and community‐level trait variance into functional richness. Trait‐specific and phylogenetic diversity patterns indicate dynamic community assembly due to variable niche expansion and packing on multiple niche axes. Locomotion and covarying traits such as tail length emerged as a fundamental axis of ecological variation, expanding functional space and enabling the niche packing of other traits such as diet and body size. Though trait divergence often explains functional diversity in island communities, we found that phylogenetic diversity facilitates functional space expansion in some conserved traits such as cranial shape, while more labile traits are overdispersed both within and between island clades, suggesting a role of niche complementarity. Our results evoke interspecific interactions, differences in trait lability, and the independent evolutionary trajectories of each of Sulawesi's six murine clades as central to generating the exceptional functional diversity and species richness in this exceptional, insular radiation.

Activity of Asiatic lions in relation to activity of prey and kleptoparasitism

Article

Full-text available

Dec 2024

Qualitative diet of Schilbe grenfelli Boulenger, 1900 (Siluriformes, Schilbeidae) caught in the Malebo Pool (Congo River) (Kinshasa, DR Congo)

Article

Full-text available

Nov 2024

The Congo River abounds in a multitude of osteichthyan fish, notably Schilbe grenfelli Boulenger, 1900 (Siluriformes, Schilbeidae), commonly known in Kinshasa as "Lilangwa" in Lingala, one of the national languages of the Democratic Republic of Congo. The species is caught in artisanal fisheries, and its flesh is highly prized for its meat. The aim of the present study was to investigate the diet of S. grenfelli, caught in the Kinshasa section of the Malebo Pool (Congo River) in the Democratic Republic of Congo. Fish specimens were collected over an eight (8), month period between february 15 and september 20, 2019. These fish were caught through artisanal fishing using bottom drift gillnets. The study of the diet was based on the qualitative aspect linked to the trophic level of the fish species under study by determining the intestinal coefficient. Trophic level results showed that S. grenfelli has a short intestine (intestinal coefficient equal to 1.89±0.12) and is considered a carnivorous fish, feeding either on zooplankton, aquatic and terrestrial invertebrates or fish present in its environment. The preliminary information provided in the present study is of great importance in that it gives indications of the trophic level of S. grenfelli fish in the Malebo Pool. This information is of great importance for knowledge of the dietary requirements of this fish for rational exploitation, but above all for fish farming, where this fish species can be domesticated to diversify Congolese fish farming.

Seasonal habitat use of ringed seals in the Thule area, northwestern Greenland

Article

Nov 2024

Qualitative diet of Schilbe grenfelli Boulenger, 1900 (Siluriformes, Schilbeidae) caught in the Malebo Pool (Congo River) (Kinshasa, DR Congo)

Article

Sep 2023

Competitive exclusion among self-replicating molecules curtails the tendency of chemistry to diversify

Article

Full-text available

Nov 2024
NAT CHEM

The transition of chemistry into biology is poorly understood. Key questions include how the inherently divergent nature of chemical reactions can be curtailed, and whether Darwinian principles from biology extend to chemistry. Addressing both questions simultaneously, we now show that the evolutionary principle of competitive exclusion, which states that a single niche can be stably occupied by only one species, also applies to self-replicating chemical systems, and that this principle diminishes the tendency of chemistry to diversify. Specifically, we report two systems in which three different self-replicator quasi-species emerge in a largely stochastic fashion from a mixture of two building blocks (resources). Competitive exclusion leads to the selection of only a single quasi-species when all replicators rely to the same extent on both resources. When one of the quasi-species preferentially uses one resource and another quasi-species specializes in the other (resource partitioning), these replicator quasi-species effectively occupy different niches and were found to coexist in an evolutionary stable steady state.

Effects of short- and long-term plant functional group removal on alpine meadow community niche

Article

Full-text available

Nov 2024

The rapid loss of global biodiversity affects the creation and maintenance of community biodiversity and ecosystem structure and function. Thus, it is insufficient to focus solely on the effects of biodiversity loss on community biodiversity without also considering other impacts such as community assembly, niches, interspecific relationships, community stability, and biodiversity–ecosystem function. In this study, a 3- and 10-year biodiversity manipulation experiment was conducted in an alpine meadow to examine the effects of the individual plant functional group (PFG) removal on the niches of community dominant species by removal of Gramineae, Cyperaceae, legumes, and other forbs. The results indicated that PFG removal led to variation in community niches. The long-term PFG removal led to a gradual decline in the number of Gramineae and Cyperaceae species in the community. Over time, the niche widths of dominant Gramineae and Cyperaceae species gradually narrowed, and the degree of niche overlapping decreased. The number of positively and negatively associated species tended to decrease and increase, respectively. Reduced species diversity led to significant differences in the niches of the remaining species within the community. Thus, species niche differences, resulting from variation in resource allocation, commonly determined the dynamic construction of species composition within the community.

Completing the Speciation Cycle: Ecological Niches and Traits Predict Local Species Coexistence in Birds Across the Globe

Article

Jan 2025

Aim The build‐up of local species diversity requires completing the transition from allopatry to sympatry to local coexistence (syntopy). However, understanding processes than enable species arising in allopatry to become syntopic remains an unsolved challenge. Potential explanations include niche conservatism, niche divergence, and energy availability. To gauge their importance, we modelled the effects of species split age, the divergence in beta and alpha niches, specialisation, and resource availability to reveal factors driving the evolution of local species coexistence upon speciation. Location Global. Time Period Miocene to the present. Major Taxa Studied Passerine birds. Methods We collated a dataset of 206 passerine sister species pairs, each with their age of divergence; range sympatry; degree of syntopy (derived from 7,257,312 complete eBird checklists falling within the area of range overlap); beta niche divergence (habitats and environmental characteristics); alpha niche divergence (morphology, diet, and foraging stratum); species ecological specialisation (diet and foraging stratum); resource availability; and body mass. We used phylogeny‐informed models to infer which of these factors best explained local species coexistence upon speciation. Results There was a major effect of niche conservatism as species with more similar beta niches (canopy height, vegetation greenness, moisture availability, and habitat affinities) exhibited higher degree of syntopy. Small species with similarly sized beaks and high specialisation on diet were also more likely to coexist locally. In contrast, the divergence or overlap in alpha niches (diet and foraging stratum) did not predict the degree of syntopy. Confirming previous studies, the degree of syntopy strongly increased with increasing range sympatry, while only weakly in older species pairs. Main Conclusions The evolution of secondary syntopy is driven by niche conservatism, ecological specialisation, and body mass‐related energy requirements. Consequently, the accumulation of local species richness is facilitated by both conservatism and differentiation along various ecological niche dimensions.

Competition

Chapter

Jan 2025

Diet and trophic niches of sympatric Seriola species revealed by stomach content and multi-tissue stable isotope analyses

Article

Full-text available

Feb 2025
FISH RES

Habitat Selection in Temperate Marsh-Nesting Birds

Chapter

Jan 1985

JOANNA BURGER

Distribution pattern and niche overlap of sympatric breeding birds along human-modified habitat gradients in Inner Mongolia, China

Article

Full-text available

Mar 2025

Spatiotemporal niche relationship between leopard and its sympatric carnivores in the forest of Baizha, Qinghai Province, China

Article

Full-text available

Nov 2024

How does the presence of dominant top predators affect the spatiotemporal dynamics of other predators in the community, it is crucial for understanding the maintain mechanisms of animal community diversity. In Baizha forest of Qinghai province, located in the southern Sanjiangyuan region, based on monitoring data of 46 available infrared camera sites collected in winter between (October to next April) from 2021 to 2023, a total of 12 carnivores species are recorded, among which the leopard Panthera pardus is the dominant apex predator in the community. By comparing the vertical spatial distribution, site co-occurrence patterns, and daily activity rhythms between species, this study explores the spatiotemporal interactions between leopard and other predators within the community. The results show: in the spatial niche dimension, leopards utilize the broadest vertical space (Altitude 3 730 - 4 433 m), primarily distributed in the range of altitude 3 900 - 4 100 m. According to the Mann-Whitney U test, the activity altitude of small mustelid is similar to that of leopard, while other carnivores are distributed at significantly higher (snow leopard, wolf, and Eurasian lynx) or lower elevations (brown bear, red fox, and leopard cat). The analysis of single-season dual-species occupancy models between leopards and other carnivores indicates that when leopard is present, wolf and red fox exhibit spatial avoidance (SIF<1); other carnivores tend to coexist with leopard (SIF>1). Elevation is an important factor affecting the probability of site use by the Eurasian lynx, Asian badger, stone marten and leopard cat. Notably, as elevation increases, the spatial relationship between the Asian badger and leopard shifts from coexistence to distinct separation. Regarding the temporal niche dimension, kernel density estimation of daily activity rhythms reveals that leopard exhibited a diurnal activity rhythm, being more active from morning and peaking at 19: 00. Wolf displayes diurnal activity; Although the daily activity does not significantly differ from that of leopard, their activity peaks are staggered. Other carnivores are mainly nocturnal, showing significant differences from the leopard’s diurnal activity rhythm, with the exception of the Asian badger. This study provides fundamental information of the composition and interspecies relationships in the carnivore community of high-altitude forest, and contributes to a deeper understanding of their coexistence mechanisms.

Fishery Biology of Sillago muktijoddhai Collected from Cox's Bazar Coast, the Bay of Bengal, Bangladesh

Article

Full-text available

Nov 2024

Microhabitats, Abundance and Food of Conus on Atoll Reefs in the Maldive and Chagos Islands

Article

Full-text available

Nov 1968

Marian Adachi Kohn (Deceased August 29 2014)

Assemblages of up to 17 species and averaging 13 species of Conus were found on topographically complex subtidal coral reefs (Type III habitat) in the Maldive and Chagos Islands, Indian Ocean. Topographically simpler intertidal smooth limestone benches (Type II habitat) supported eight species. At a station with intermediate habitat, 12 species were present. Only two species were found in extensive areas of sand substrate (Type I habitat). Although most of the commoner species occurred in habitat Types II and III, their relative abundances differed strikingly. Species characteristic of the physically harsher, topographically simpler Type II environment are smaller, sometimes occur in dense populations of up to 1 individual/m"2, and are quite specialized predators on herbivorous errant polychaetes. Species characteristic of the more equable but topographically diverse Type III environment are larger, have lower population densities of 0.03-0.15 individual/m"2, and are somewhat more generalized predators on deposit-feeding sedentary polychaetes. Detailed analysis of diets supports the conclusion of prior studies that most species of Conus are primary carnivores. The 13 most abundant species of Conus in the Maldive and Chagos Islands feed almost exclusively on polychaetes, which comprised 96% of all food items identified. Species that eat gastropods and fishes were present but uncommon. The nature of the food of eight species was determined for the first time. Calculations of amount of food eaten, based on rather crude data for five species, gave a mean of about 10% of body weight eaten per day, but some of the estimates seemed unreasonably high. Species with more specialized diets are larger numbers of prey items than generalists, but the larger ratio of prey size to body size of the latter probably compensates, so that specialists are not more successful predators than generalists. In the habitats studied, Conus species are not more specialized predators where larger numbers of congeners co-occur. The topographic uniformity and less patchy nature of Type II habitat probably favor both increased density of the prey and mobility of Conus, thus making appropriate food more abundant and accessible than in Type III habitat. Conus diets are correspondingly more specialized in Type II than Type III habitat. These opposite feeding strategies foster increased feeding efficiency in the two topographically contrasting habitats. It is proposed that topographically simpler, more uniform, intertidal bench habitats favor lower species diversity, specialization, smaller body size, and higher population density, while topographically more complex, patchier, slightly subtidal coral reef habitats favor higher species diversity, somewhat more generalized habits, larger size, and lower population density.

On the Ecological Significance of Bergmann's Rule

Article

Full-text available

Sep 1971

Brian K Mcnab

A positive correlation of weight with latitude in homoiotherms (Bergmann's rule) cannot normally depend upon the physics of heat exchange. Most latitudinally widespread mammals in North America do not follow this rule. Those that do are usually carnivores or granivores; a change in their body size reflects a change in the size of their prey. A latitudinal change in the size of available prey is due either to the distribution of the prey species or to the distribution of other predators utilizing the same prey species. Only the smallest species of a set of similar predators normally will conform to Bergmanns rule, and then only beyond the limits of distribution of the largest species. These changes in size seem to be another example of character displacement.

Habiitat Restriction by Competitive Exclusion in the Mice Peromyscus and Mus

Article

Jan 1967
Can Field Nat

Walter Sheppe

THE LION

Chapter

Jan 1972

P. T. Eden

Principles of natural coexistence indicated by leafhopper populations

Article

Jun 1957
EVOLUTION

Herbert H. Ross

THE EVOLUTION OF BILL SIZE DIFFERENCES AMONG SYMPATRIC CONGENERIC SPECIES OF BIRDS

Article

Jun 1965
EVOLUTION

Thomas W. Schoener

THE PERIODICAL CICADA PROBLEM. II. EVOLUTION

Article

Dec 1966
EVOLUTION

THE TEMPORAL COMPONENT OF DIVERSITY AMONG SPECIES OF BIRDS

Article

Jun 1966
EVOLUTION

Robert E. Ricklefs

Distribution, Coexistence, And Competition Of Whirligig Beetles

Article

Jun 1966
EVOLUTION

Conrad A. Istock

https://deepblue.lib.umich.edu/bitstream/2027.42/137467/1/evo03357.pdf

INFLUENCE OF INTERSPECIFIC COMPETITION AND OTHER FACTORS ON DISTRIBUTION OF BARNACLE CHTHAMALUS STELLATUS

Article

Oct 1961

Joseph H. Connell

The natural control of insects in pinewoods. I. Factors influencing the intensity of predation by songbirds

Article

Jan 1960

L. Tinbergen

The Life Cycles of Two Sympatric Species of Ichnotropis (Sauria: Lacertidae)

Article

Jan 1967

D.G. Broadley

Pattern and Process in Competition

Chapter

Dec 1967
ADV ECOL RES

Richard S. Miller

This chapter discusses the development of competition theory, which has traditionally included three stages: inferences drawn from observation of natural populations, construction of mathematical models, and laboratory experiments designed to test elements of competitive interactions in controlled environments. Interference to any activity either directly or indirectly limits a competitor's access to a necessary resource or requirement. Different types of evidence are assigned for competition in nature. Principal categories are mutually exclusive spatial distributions without supporting evidence of a competitive interaction, observed or inferred ecological displacement in sympatric populations, and induced changes in distribution pattern. A considerable amount of ambiguity exists in interpretations of the results of interspecies competition. It is necessary to distinguish between maximum exploitation of the available resources by one species, and equitable utilization of the resources and possible coexistence in a mixed species system. The chapter suggests two major sources of species diversity. When competition is primarily through exploitation and the system is under strong environmental control, it is likely that fluctuations in factors affecting reproduction and survival will continually alter the outcome of the competitive interaction, allowing coexistence of mixed species populations.

The Vertical Distribution and Feeding Relationships of Intertidal Fish on the Atlantic Coast of France

Article

Feb 1972

R. N. Gibson

(1) The results of several collections of tide-pool fishes made along transects in the rocky littoral zone near Roscoff in Brittany are described. (2) The fish were found to occupy fairly distinct zones on the shore and three groups of species were recognized. Those occupying the whole intertidal zone, those restricted to the upper levels, and a third group which were found only on the lower parts of the shore. The nature of the shore was found to have a considerable effect upon the density, distribution and species composition of the fish populations. (3) Multiple correlations indicated that for the commonest species, Blennius pholis, Gobius paganellus and G. cobitis, few of the measured variables on the shore, level, per centage cover, and surface area of the pools in which the fish were found, accounted for more than about one third of the variation in numbers. Also, the importance of these three factors varied with each species. (4) The `typical habitats' of the commoner species are described and compared. (5) The food of all species, as determined from their stomach contents, is described. Three groups of feeders are recognized; crustacean feeders, omnivores and carnivores. The differences in diet between species is discussed in relation to competition and distribution. (6) The factors causing differences in vertical distribution and habitat are discussed in relation to the classical concepts of littoral zonation.

Temperature Responses and Ecological Relations of Two Bornean Lizards

Article

Jan 1959

Robert F. Inger

The Periodical Cicada Problem. II. Evolution

Article

Dec 1966

As any scientist knows, a theory must not be judged by its plausibility or lack of it, but by how well it can anticipate new discoveries. The most important things for us to summarize, therefore, are the new things to look for. We need to know a great deal more about the developmental periods of non-periodical cicadas. On purely demographic grounds, a long pre-reproductive period should be a severe disadvantage; other things being equal, it should be strongly selected against. In view of the data in Table 2, one must postulate some counter-advantages for the long developmental periods characteristic of cicadas. As one hypothesis, we suggest in Table 3 a counter-advantage connected with loud song, large size, and obligately slow feeding. This idea could be exploded by finding a large cicada with a short life cycle, provided its feeding habits are typical of cicadas in general. The current work of Anderson and Shorey with Diceroprocta apache on asparagus roots (see earlier footnote) may provide exactly the disproof that is needed. With the advent of nearly-perfect periodicity, the rules are considerably changed. Given that there already is a long life cycle, the above-ground predators become satiated, and the below-ground ones deprived of food, by every periodical emergence (Lloyd and Dybas, 1966). The prey can now evolve predator-foolhardy behavior, especially as old behavior patterns may be incompatible with the demands of reproduction at enormously elevated population densities. The most severe selective penalties are now levied against those individuals that fail to emerge along with the majority; either a lengthening or shortening of the life cycle would be selected against under these circumstances. As between two competing cicada populations with equally perfect periodicities, however, the shorter life cycle should still have an advantage. Thus, we anticipate that 13-year broods should now be displacing 17-year ones wherever their ranges are contiguous, as, for example, XIX and XXIII supplanting IV in the Ozarks (cf. Figs. 7A-B and 6G). This idea can obviously be tested by detailed mapping of future emergences and historical records. In the course of evolution towards periodicity, phenotypic variability in the developmental period would acquire a maladaptive significance that it could never have had before. The fact that immature periodical cicada nymphs are as variable in size as they are (Fig. 1) must mean that these species have some special physiological mechanism (i.e., something other than a very uniform growth rate) which insures that the nymphs will emerge together after 13 or 17 years-some mechanism like "counting" diapauses, for example. The elucidation of this physiological mechanism is a worthwhile research objective in its own right. The ecological theory predicts that no such mechanism will be found in any non-periodical cicada, because it would have no selective advantage without the periodicity. We need, therefore, to know something about the variability, as well as the mean duration, of developmental periods in non-periodical cicadas. Looking back to an evolutionary stage before the physiological timing mechanism and the periodicity were perfected, we can imagine that strong selection would have been necessary in order to prevent the incipient periodicity from disappearing of its own accord. How strong would depend, of course, on how great was the variability in the developmental period (Fig. 2). We can also imagine population interactions taking place between "protoperiodical" cicadas and their predators that one would not expect to see taking place now. If cicadas were to appear above ground for several consecutive years (with a hiatus in between), then populations of parasitoids with life cycles of one year (living on alternative hosts during the hiatus) would build up, as shown in Fig. 3. This idea predicts that the alternative hosts of parasitoids that attack periodical cicada eggs or adults should suffer much greater mortality rates from parasitoid attack in the year after a periodical cicada emergence than in the year prior to one. Unfortunately, this would be a difficult thing to measure, since the alternative hosts will generally be comparatively rare. Another testable prediction is that wherever two periodical broods one year out of phase have adjacent ranges (see I-II, III-IV, V-VI, VIII-IX, IX-X, XXII-XXIII, Figs. 6 and 7), the leading brood should gradually be supplanting the lagging brood. Moreover, this should be occurring even where the population densities are so low that underground competition for feeding sites is not likely to be important, i.e., at densities of fewer than five mature nymphs per square yard. If this is, in fact, a tenable idea, then it creates difficulties with the theory, because the interaction with year-to-year parasitoids would produce a strong selective pressure favoring ever-shorter developmental periods in protoperiodical cicadas (see Fig. 3). We could accommodate this by assuming that the protoperiodical ancestor had a life cycle even longer than 17 years but, if that were true, one would expect to find life cycles of this length in present-day non-periodical cicadas. None have turned up so far, and the pattern of developmental periods relative to body size (Table 2) suggests that none are likely to be found. As an alternative explanation, we are led to postulate something which can never be verified directly: a parasitoid with a life cycle of many years duration, nearly synchronized with the protoperiodical cicadas and exerting a counter-selection pressure favoring a longer life cycle. Since there is no trace of such a parasitoid now, we have to assume that it became extinct. We cannot assume that this hypothetical parasitoid was one that attacked the cicada nymphs, because we would then have no explanation for the apparent absence of this kind of life cycle in parasitoids of present-day non-periodical cicadas. We are left with a hypothetical parasitoid attacking eggs or adults, which implies a long period of dormancy underground. The only documented case of this that we know about is the report of Tillyard (1926) concerning two- or three-year dormancy in larvae of the Australian cicadahunting wasp, Exeirus lateritius. However, the startling data of Barnes (Fig. 4) suggest that long dormancy underground is possible, even for small insects. The testable prediction the theory makes, then, is that prolonged underground dormancy of this kind will prove to be a great deal more common and widespread among insect parasitoids than is generally realized. An alternative hypothesis to account for the evolution of exceedingly slow developmental rates in protoperiodical cicadas assumes very high population densities, severe competition for food, and a spectacular ability on the part of certain genotypes to withstand prolonged periods of starvation. There is no apparent reason why periodical nymphs should not still retain this ability, so this idea is testable also. In addition to the very long life cycles themselves, any comprehensive theory must be able to account for both the 13-year and 17-year life cycles (both perfectly periodical), for the various broods within each life cycle (Figs. 6 and 7), and for the three sibling species (or species pairs, see Table 1)-species that coexist sympatrically within each brood, within either life cycle. In Fig. 6E, we adopt the suggestion of Alexander and Moore (1962) that adjacent broods one year out of step arose by summation of diapauses, resulting perhaps from unseasonable cold in a particular year, and we add to this the further hypothesis that accelerations of four years can also take place. This leads us to postulate that the 17-year cicadas differ from the 13-year ones by the possession of a supernumcrary sixth instar. There is at present no convincing direct evidence for this sixth instar in 17-year cicadas, but the assumption that it exists, and can be omitted from the life cycle in response to some environmental shock, enables us to postulate a mechanism for deriving a fully-periodical 13-year life cycle directly from a fully-periodical 17-year one, without losing the periodicity in the process. Fortunately, the question of a supernumerary sixth instar is directly testable. Present efforts are being directed towards that end. As one would expect, the habitat preferences of the three species differ. Dybas and Lloyd (1962) described these differences for Magicicada septendecim and M. cassini. A future paper will treat all three species, with both 13-year (Brood XXIII) and 17-year (Broods II, III, IV) life cycles. We find the same habitat differences among the three species, whatever the life cycle, whatever the brood. The ecological tie that has kept these three species in perfect synchrony with one another, through all this evolution of different broods and life cycles is, by hypothesis, the same mechanism that was originally responsible for selecting in favor of periodicity-the possibility of satiating predators and, given that predators are satiated, the selective penalties against (predator-fool-hardy) individuals that do not emerge in synchrony with the group. A few such individuals still occur, sometimes even several years out of synchrony. These "stragglers" are probably seldom reported in the literature, presumably because their significance is not generally appreciated.

Species Relationships and Adaptations for Sympatry in the Avian Genus Vireo

Article

Jan 1962

Terrell H. Hamilton

Food Overlap Among Coexisting Sandpipers on Northern Alaskan Tundra

Article

Sep 1968
Syst Zool

Evolution of Niche Width

Article

Nov 1972

Jonathan Roughgarden

A model is developed to predict evolution in a population which contains a variety of ecologically specialized phenotypes. Individuals of each phenotype are assumed to specialize on a specific region of a resource axis present in the environment. The model, incorporating density-dependent effects on the fitness of the various phenotypes, predicts the number of individuals of each phenotype through time for both asexually and sexually reproducing populations. The lizard species, Anolis roquet, illustrates the kind of population treated by the model. The resource axis is prey size; small lizards preferentially utilize small prey, while large lizards exploit large prey. Field data on this species are used to estimate some of the parameters of the model. The model shows that there is an optimum number of individuals of each phenotype for a given set of resources and a given regime of interphenotypic competition. If the population has this optimum distribution of individuals, then the fitnesses of all phenotyp...

The Ecological Theater and the Evolutionary Play.

Article

May 1967

Sexual Dimorphism and Food Habits in Three North American Accipiters

Article

Jul 1966

Robert W. Storer

Trophic Relationships of 8 Sympatric Predatory Gastropods

Article

Jan 1963

Robert T. Paine

Analysis of Simple Cave Communities: Niche Separation and Species Packing

Article

Nov 1970

David C. Culver

This paper considers various ecological relationships of three gammarid amphipods (Gammarus minus, Stygonectes emarginatus, and Stygonectes spinatus) and one asellid isopod (Asellus holsingeri) in cave streams of the Greenbrier Valley in West Virginia. Two clear-cut cases of reduction of realized niche due to the presence of other species were found: S. emarginatus is limited to small trickles of water when G. minus is present in the stream and A. holsingeri is limited to gravel-bottomed pools when G minus is present in riffles. S. spinatus prefers smaller rocks than do the larger amphipod species. All four species maintained weight equally well on rotting leaves or mud, so feeding differences appear to be minimal. Using Levins' matrix of competition coefficients as a framework, interference and exploitation competition were quantified and separated. From these data, it is indicated that the community is closed to immigration by similar species into the microhabitats occupied by the four crustacean species. Field evidence supports this. Some unused microhabitats may be available, but the aquatic insects that might potentially use them are not present.

Resource Partitioning in Species of the Water Mite Genus Eylais

Article

Mar 1970

Carmine A. Lanciani

Resource partitioning was studied in 20 species of the water mite genus Eylais, the larvae of which parasitize adult Coleoptera and Hemiptera living in shallow ponds. Co-existence of sympatric species is possible because the mites exploit host resources in different ways. Most commonly they parasitize different species, but when hosts are identical, the mites remain segregated by differences in the precise site of attachment, biotope, or season of parasitism. Mite biology, host dispersal, and competition for attachment sites from other water mite species may restrict further subdivision of host resources.

Niche Segregation in Seven Species of Diplopods

Article

Nov 1967

Robert V. O'Neill

Competition Between Two Chipmunk Species (Eutamias)

Article

Mar 1971

David H. Sheppard

Two chipmunk species were studied in the mountains of western Alberta from 1961 to 1965. One species, Eutamias minimus, is largely confined to alpine habitat but also ranges into subalpine forest, where its distribution narrowly overlaps that of E. amoenus. The fundamental niches of the two species, estimated from their habitat distributions elsewhere, are both reduced in western Alberta. Mark and recapture trapping in an overlap zone showed that neither species selected habitat deficient in cover and both species made the same relative use of the available forest. The boundary between the two species was not clearly predictable by obvious habitat features. Eutamias amoenus luteiventris is larger than E. minimus oreocetes and, on an average, has larger litters, earlier maturity, and higher populations density. The two species take similar foods, depending on availability in their respective habitats, but the food consumption of individual minimus is less than that of amoenus. In the laboratory, amoenus was highly successful in interspecific encounters with minimus, regardless of whether or not minimus was a resident of the observation cage. In addition, amoenus dominated minimus in a mixed-species group and minimus exhibited avoidance behavior under such conditions. The highly developed aggressive behavior of Eutamias amoenus enables it to exclude E. minimus from subalpine habitats, but the latter survives in alpine situations where its small size is an adaptation to a reduced food supply.

The Evolution of Bill Size Differences Among Sympatric Congeneric Species of Birds

Article

Jun 1965

Thomas W. Schoener

This paper presents the results of an analysis of bill length differences among sympatric congeneric species associations of 46 bird families inhabiting tropical, subtropical, and temperate areas. The bill ratios of large to small species within these associations, called ratios of character difference are usually large (greater than 1.14) 1) among the members of certain families which appear to feed on food of relatively low abundance; 2) in sympatric congeneric species associations on islands, especially small islands; and 3) among birds whose body sizes are relatively large in proportion to the total abundance of their food. Large ratios are assumed to reflect significant differences in dimensional or physical properties of the food or its immediate environment. Models considering the distribution of food biomass with respect to size are used to argue that where the diversity of potentially competing species is low, due to low food abundance relative to the size of the feeding birds or for other reasons, food partitioning by size or dimensional property of the immediate food environment as a means of avoiding competition is feasible. In contrast, where a large number of potentially competing species occurs, as is likely to be the case for birds which consume relatively abundant food, rather than evolve the precise perceptual mechanisms necessary for discriminating small food size spans if food partitioning by size is to be utilized, species will consistently avoid competition by evolving differences in feeding habitat or foraging behavior. It is suggested that the most probable first step in the evolution of sympatric congeneric associations on islands and in some mainland situations is the partitioning of food by size, physical properties, or dimensional properties of its immediate environment, rather than by habitat. The first species to invade an area is likely to expand its habitat considerably, but still feed on a rather restricted range in dimensional or physical properties of the available food or its immediate environment, due to limitations of structure and efficiency on the individual bird, resulting in the most favorable opportunities for colonization by closely related species leading to coexistence to be for the invading species which utilize different ranges of these properties. The utilization of different food size ranges in many and overlapping habitats as opposed to taking similarly-sized food in different, more restricted habitats, being the more complete utilization of the available food supply for a small number of species, also favors the initial evolutionary step resulting in large ratios of character difference. Many insectivorous families, but only a small proportion of others, all of whose small-billed associations have small ratios of character difference, possess other associations in which the largest or larger species are separated from the other members by a relatively large character difference, and have still other associations, entirely composed of large-billed birds, with high ratios among all members. Two possible explanations are larger consuming biomasses for the larger species of an association and a food abundance distribution curve which decreases with increasing food size. The transition zone, defined as the range of bill length over which small ratios change to larger ones (greater than 1.14), begins at smaller bill lengths in insectivorous families than it does for more omnivorous groups. Insectivorous families in general show more large ratios in tropical areas than in temperate zones, related to the much greater number of large-billed tropical insectivorous birds. This preponderance can be explained by a lower consuming biomass of populations of tropical species and/or a less sharply declining food abundance distribution curve with increasing food size for insectivorous families in the tropics. Some implications of this study for the concepts of niche overlap and behavioral stereotypy are discussed.

The Feeding Relationships of Salmon, Trout, Minnows, Stone Loach and Three-Spined Stickle-Backs in the River Endrick, Scotland

Article

Feb 1965

Peter Maitland

1. The food of salmon, Salmo salar L.; trout, S. trutta L.; minnows, Phoxinus phoxinus (L.); stone loach, Nemacheilus barbatula (L.); and three-spined sticklebacks, Gasterosteus aculeatus L., in the River Endrick, Scotland, was assessed by examining the stomach contents of 1435 specimens of these fish. 2. Most fish were taken from a single tributary stream, the Altquhur Burn, and the composition of its bottom fauna was estimated by taking monthly samples from the dominant substrate. 3. Though the diet of each of the five species of fish was characteristic in some way, all were found to feed on the common aquatic invertebrates present (e.g. Baetis, Gammarus and Orthocladius). 4. Surface organisms formed a large part of the food of trout but were less important to salmon and minnows, and only rarely taken by stone loach and three-spined stickle-backs. 5. The availability of certain invertebrates to fish was assessed by comparing the composition by bulk of the bottom fauna with that of the aquatic invertebrates eaten by each fish species. The common invertebrates present exhibited availability factors which varied from one species to another, and which also depended upon which fish species was involved. 6. Competition among the five species of fish concerned is discussed: it appears that whilst each species has a characteristic diet, all have food items in common and competition among them is likely--its degree probably being determined by the abundance of the food items being competed for.

The Ecological Distribution of Grapsid and Ocypodid Shore Crabs (Crustacea: Brachyura) in Tasmania

Article

Oct 1971

D. J. G. Griffin

(1) The distributions of the nine grapsid and two ocypodid species of shore crab in Tasmania are described in relation to substrate, cover, wave action, salinity and major tidal levels on the shore. The breeding and moulting cycles, the number and relative volumes of the gills and the arrangement of particular types of hairs on the mouthparts are described. Their behaviour in the laboratory, in relation to freshwater, immersion in water, substrate and cover, is considered and compared with their apparent behaviour towards these factors in nature. (2) The major factors determining the species' distributions appear to be substrate, availability and type of cover, salinity range, exposure to wave action and length of time for which particular shore zones are uncovered by water. (3) Although the distribution of each species overlaps that of others, each is most abundant in a particular type of habitat where other species do not occur in maximum abundance. Juveniles have a wider distribution than adults. (4) More species occur in the midlittoral area of stony beaches sheltered from heavy wave action than in any other habitat. (5) Each species shows a number of morphological, physiological and behavioural adaptations to its characteristic habitat. Although the niches of most of the species are broad there is no evidence that interspecific competition is important in determining their limits.

Food Competition Among the Cellular Slime Molds (Acrasieae)

Article

May 1971

Edward G. Horn

Four species of Acrasieae (Dictyostelium mucoroides, D. purpureum, Polysphondylium pallidum, and P. violaceum) coexist in forest soils. All are capable of feeding and reproducing on a wide variety of bacteria than exist in their habitat. The four Acrasieae and four strains of food bacteria were isolated from the soil. When the four slime molds were forced to compete on a single strain of bacteria, one species always outcompeted the others. For any particular food the same species of Acrasieae is the consistent winter. Each species uses a different strategy to outcompete its competitors. The consistency of competitive success and the "coarse-grained" nature of the food distribution allow the coexistence of these four species of Acrasieae in nature.

Three Central American Bat Communitis: Structure, Reproductive Cycles, and Movement Patterns

Article

Jul 1972

Three bat communities were studied for 1 year at each of two localities in the Panama Canal Zone and one locality in western Costa Rica. Removal sampling and banding techniques using Japanese mist nets were employed to document community structure, food habits, reproductive cycles, and movement patterns of these bats. Results indicated that 27-31 species occur at or near ground level at each locality. Species diversity, as measured by H', was highest in the Costan Rican community; each community contained 3-4 common species and many uncommon species. Based on body size and general food habits, niche overlap appears to be greatest among small to intermediate-sized insectivores and frugivores, many of which, however, are apparently uncommon. Four basic reproductive patterns are found among the species. Most frugivores are seasonally polyestrous whereas some insectivores are monestrous and at least one is polyestrous. It is postulated that in both insectivores and frugivores birth peaks coincide with maximum food levels. Recapture patterns of several species suggest that home range size may be positively correlated with body size; omnivorous species may have larger home ranges than similarly size species with more restricted diets.

Coexistence, Coevoluation and Convergent Evolution in Seabird Communities

Article

Jan 1973

Martin L. Cody

Ecological isolating mechanisms based on differences in size or breeding season operate in many groups of related sympatric seabirds, but not in the alcid species (Aves: Fam. Alcidae) found together in Washington State. At least three of the six coexisting species have similar diets, and all six breed at the same time of year. They differ, however, in their foraging zones at sea and appear to have reduced interspecific competition by this means. Diverse aspects of the breeding biology, behavior morphology and ecology of these alcids can be explained by reference to two sets of selective factors--interspecific competition for food and predation upon the eggs, chicks and adults. Species that fish inshore guard their chicks in exposed cliff sites grouped into ubiquitous but small colonies. They carry fish to chicks singly and frequently throughout the day. These young develop rapidly to about one-third adult weight, at which time they quit the nest site. At the other extreme, species that feed far offshore provide burrows for the chick and nest in large colonies on only a few off-shore islands. Chicks are visited at night by adults whose bills are adapted for carrying many fish. These chicks grow slowly and reach close to adult weight before leaving the nest. These patterns are repeated with considerable fidelity in the six-species alcid community of Northern Iceland, but southern hemisphere seabirds are, in general,differently organized.

The Analysis of Multidimensional Contingency Tables

Article

May 1970

Stephen E. Fienberg

Ecological data often come in the form of multidimensional tables of counts, referred to as contingency tables. During the last decade several new methods of analyzing such tables have been proposed. Here, a class of models analogous to those used in the analysis of variance is discussed, and a method for computing the expected cell counts for the different models is presented. Two differenet tests for checking the goodness-of-fit of a particular model are then examined. The first is the simple generalization of the Pearson chi-square test statistic, while the second is referred to as the likelihood-ratio chi-square test statistic. Both have the same asympototic @g^2 distribution. The likelihood-ratio statistic can be used in the selection of a suitable model, via the technique of partitioning. All of the methods presented are illustrated using data collected by Schoener on lizards from the West Indies.

Ecological and Competitive Relations Among Three Species of Frogs (Genus Rana)

Article

Sep 1966

Interspecific competition is often advanced as an explanation for replacement of species by ecological counterparts. Where environments are stable, as in controlled laboratory experiments, interspecific competition usually leads to the extinction of one species. In a complex natural environment, fluctuations in physical and biotic factors may long delay competitive exclusion. The existence of three related species of frogs (genus Rama) confined to stream in tropical rain forest provided an opportunity to manipulate natural populations and thus to study the relation between overlap in niches and interspecific competition. A rain forest area was chosen because it lacks significant seasonal variation in rainfall, temperature, and photo-period and consequently prevents seasonal specialization of the fauna. These three species, R. blythi, R. ibanorum, and R. macrodon, proved to be very similar in habits. Rana blythi is larger than the other two and usually was found farther from the stream bed. Rana macrodon reaches sexual maturity faster than the others and R. ibanorum lays fewer eggs. Nonetheless it is clear that their niches overlap extensively. Populations of these frogs were studied on surveyed portions of three streams by mark and release techniques. Populations of R. blythi on one stream (Sungei Ensurai) and R. ibanorum on another (Sungei Sekentut) were initially much smaller than the respective populations on the other streams. Following removal of R. blythi from Sungei Sekentut and of R. ibanorum from Sungei Ensurai, leaving the populations on Sungei Serbong as controls, R. blythi on Sungei Ensurai appeared almost to double in numbers and to reach the population levels originally found on the other streams. Population estimates of R. ibanourm on Sungei Sekentut fluctuated, being larger at midyear; statistical support for this variation is weak. Rana macrodon seemed to quadruple its numbers on Sunge Sekentut. There is evidence that macrodon is in the process of invading this part of Borneo and may be doing so at the expense of R. ibanorum. Maximum population levels for the blythi and ibanorum may be fixed by intraspecific competition, which in turn may be responsible for maintaining the coexistence of these related species.

The Psocid Fauna of Larch Trees in Northern England--An Ecological Study of Mixed Species Populations Exploiting a Common Resource

Article

Nov 1958

Edward Broadhead

1. Nine psocid species make up over 95% of the psocid population on larch trees (Larix decidua Mill.) in the Pennine region of northern England and are the most important animals exploiting the microflora on the bark. This consists of lichen (Lecanora conizaeoides Cromb.), Pleurococcus sp. and fungal spores. 2. Feeding preferences and the effect of food upon oviposition-rates have been investigated by laboratory experiment. Seven species prefer Pleurococcus to lichen. When both these foods are available, little lichen is taken; when lichen only is presented, oviposition-rates fall and they gradually starve. Two species prefer lichen to Pleurococcus. 3. Reuterella helvimacula eats the whole lichen. Mortality- and oviposition-rates on Pleurococcus are the same as on lichen. 4. Elipsocus mclachlani prefers lichen but feeds only on the apothecia; its oviposition-rate on Pleurococcus is greater than that on lichen. 5. The six Pleurococcus-preferring species feed mainly in nature on Pleurococcus and fungal spores. 6. Each species has the same habitat in all stages of its life history, and the nymphs eat the same foods as the adults. 7. The nine species fall into two phenological groups. The two Mesopsocus species overwinter as eggs, develop early in spring, become adult in June, and have only one generation a year. The others also overwinter as eggs but develop later, becoming adult in August and September; they also have one generation a year. Nymphs and adults of Reuterella helvimacula and Elipsocus hyalinus can survive the winter in the lowlands, but not at higher altitudes. 8. Mesopsocus unipunctatus occurs at all altitudes, M. immunis only below 800 ft; Elipsocus mclachlani occurs only above 600 ft, and the remaining six species are present at all altitudes. Among the late summer species, the two lichen-feeders and the three commonest feeders on Pleurococcus and fungal spores all show denser population levels with increasing altitude. 9. In twenty-one of the twenty-four plantations sampled in late summer, two, three or four species feeding on Pleurococcus and fungal spores occur at moderate or high densities on the same trees at the same time; in five plantations three species live together at high densities even though Mesopsocus species are grazing these foods earlier in the season. 10. There has been adequate time for colonization of these larch plantations by all the species except Reuterella helvimacula. 11. The nine species studied include three groups of closely related species, but the members of each group differ in microhabitat. Amphigerontia contaminata predominates on living twigs, A. bifasciata on dead ones; Elipsocus westwoodi lives mainly on living branches, E. mclachlani is almost restricted to dead ones, and E. hyalinus is intermediate; the two Mesopsocus species differ less and their populations overlap spatially. 12. Experiments with Elipsocus westwoodi and E. hyalinus confirm that factors other than abundance of food play a part in habitat selection. The distribution of the two lichenophilous species on a larch tree corresponds closely to that of their food. 13. For the late summer species the absolute densities at two highland and one lowland plantation were measured. At the highland localities the distribution of the various species closely followed that of their foods. The populations of the three Pleurococcus-feeding species were here highly interspersed at high densities. Average densities of 7.7 psocids per 10 cm of living twig and 5.9 per 10 cm of dead twig were found at Witton Fell. At the lowland locality the distributions of the four common Pleurococcus-feeders differ and show no close correspondence with that of their food; their populations overlap considerably. 14. In one lowland plantation two Mesopsocus species were present in almost equal numbers and averaged 1 individual per 5.8 cm length of twig. On twigs of any one type, these two species appear randomly interspersed. 15. The problems presented by the coexistence of these abundant species exploiting the same food at the same time are briefly discussed.

Coexistence and Anatomical Similarity in Two Genera of Mites, Veigaia and Asca

Article

Sep 1968
Syst Zool

Henry W. Hurlbutt

Ecologic characteristics of species of two genera of soil mites. Veigaia and Asca, were investigated. Among ten species of Veigaia, all collected from deciduous forests in central Maryland, there were considerable differences in vertical distribution: some species were restricted to leaf litter, some occurred mainly down in the A1 layer, and others were intermediate. There were also marked dissimilarities in overall size and in length and form of the chelicerae. These differences probably were related to differences in kinds of prey captured. Species of Asca were separated partly by habitat and partly by differences in cheliceral dentition. The relationship between anatomical similarity and frequency of coexistence was investigated. Moderately similar species were found together more often than markedly dissimilar forms. Very similar species were found together rarely or not at all.

Community Ecology of Some Tropical Rain Forest Butterflies

Article

Jan 1972

Allen M. Young

Marked individuals of several species of butterflies were studied for 5 months at a natural food source (fallen fruits of Coumarouna oleifera trees) in a tropical rain forest in northeastern Costa Rica. When the marking program was begun, the number of adults at each of four feeding sites was low and remained so during the study period as there was very little recruitment of new (unmarked) adults. Distinct diurnal patterns of feeding were noted for the different species, and species preferences for feeding sites (microhabitats) and times for feeding were estimated as niche breadths. Niche breadths were also calculated for food preferences in an experimental study where various fermenting artificial fruit baits were intermingled with the Coumarouna fruits at one feeding site. The results of this study indicate that this butterfly community is very stable, both spatially and temporally, which is of interest with respect to current ecological theory on community structure. These species do not segregate with respect to either microhabitat (feeding site) or food (various baits). The observed temporal segregation of feeding time by these species is probably a mechanism of aggregation associated with other activities of the butterflies. Competitive interactions permitting co-existence must be sought elsewhere in the ecology of these species, and it is speculated that these processes may be in the immature components of each species population.

Feeding Niches of Hummingbirds in a Trinidad Valley

Article

Jun 1972

(1) An account is presented of the feeding habits of the nine species of hummingbirds which are common in the forested lower Arima Valley in Trinidad. (2) Three `hermit' hummingbirds have long decurved bills, occur primarily in forest and feed mainly close to the ground, principally at the flowers of herbaceous plants. The six other species have more or less straight bills and mainly frequent more open areas. The two largest species of this group feed almost entirely at the flowers of large trees and vines; three of the smaller species feed on a wider variety of flowers, and the fourth feeds mainly at high trees in the open. (3) The flowers at which the hermits feed mainly have corolla-tubes which fit the hermits' beaks closely. The flowers at which the other species feed are more diverse. Within both groups, the hermits and the others, the large species feed almost entirely at large flowers, apparently because they cannot obtain enough nectar from small flowers for it to be worth their while to visit them. Small hummingbirds, on the other hand, feed at both small and large flowers providing that they can obtain nectar from them. The length of time spent at a flower appears to be a good measure of the amount of nectar available. (4) All nine species also feed on insects to some extent. Those for which there were sufficient records showed clear differences in their insect-foraging techniques. Taking into account both nectar- and insect-feeding, most of the species are well separated in their feeding habits. Three small species which appear to be most alike in feeding habits are largely separated by habitat. (5) The suggestion is advanced that in the evolution of hummingbirds there may be a critical size (which may not be the same in all areas), below which they compete with insects for the nectar of small unspecialized flowers, and above which they are able to evolve in parallel with specialized flowers which by their size and structure exclude most insects. The predominance of only one main stock of hummingbirds--the hermits--at low levels in tropical forest, and the opportunity for more rapid evolution of flower characters in herbaceous plants than in trees, may account for the close matching of the hermits' beaks to the corolla-tubes of the main flowers at which they feed.

Food Niche and Co-Existence in Lake-Dwelling Triclads

Article

Oct 1970

(1) The proportions of certain abundant organisms in the natural food of Polycelis tenuis, P. nigra, Dugesia polychroa and Dendrocoelum lacteum have been determined by means of a serological technique. The triclad populations of twelve lakes, involving tests of 2282 triclads, have been examined. (2) The food niches of Polycelis tenuis and P. nigra as a unit, Dugesia polychroa and Dendrocoelum lacteum overlap but the first-mentioned feeds to a greater extent on oligochaetes, the second on gastropods and the third on Asellus. Such contrasts are maintained throughout the year. (3) Comparison of the size of sub-food niches, distinguished by the type of prey, shows that they fall into two classes. Those in which the difference between triclad species averages 10.4% of the total food and those in which it averages 46.2%. The latter are referred to as `food refuges'. (4) It is suggested that co-existence of these triclads is possible only if the specific `food refuge' of each is found in the lake. (5) In support of this hypothesis, it was shown that the distribution of Dendrocoelum lacteum is associated significantly with its `food refuge' Asellus; it is not linked, for example, with the distribution of Gammarus, another prey taken in lesser amounts. (6) There is some evidence that the two Polycelis species are able to partition the oligochaete sub-niche so that Tubificidae provide a `food refuge' for P. tenuis and Naididae for P. nigra.

Termite Distribution in Man-Modified Habitats in West Africa, with Special Reference to Species Segregation in the Genus Trinervitermes (Isoptera, Termitidae, Nasutitermitinae)

Article

Oct 1965

WA Sands

1. Mound population densities of Trinervitermes ebenerianus in Northern Nigeria have been shown to be higher in a cleared subsere dominated by grasses (area III) than in either a scrub plagioclimax (area II) or an open woodland (area I) composed of similar plant species. The mounds tended to be aggregated. 2. In the genus Trinervitermes, the five species were found in different parts of the habitats. T. ebenerianus was most frequent in open sites, and T. oeconomus and T. auriterrae in shade. T. suspensus was largely restricted to mounds of other species. T. carbonarius seemed to have requirements that overlapped with T. ebenerianus but tended to occur on raised sites such as natural hummocks and old mounds of Macrotermitinae. It was uncommon compared to T. ebenerianus, probably because less well adapted to the climatic conditions of the area. 3. Observations on mound sharing by ants and termites suggest that mounds unoccupied by their original builder more often had secondary occupants than did `live' mounds. Where the population density was lower, proportionately fewer mounds were shared, possibly because existing mounds were more permanently occupied by their original builders. 4. Subterranean genera such as Anoplotermes, Microtermes, and Pseudacanthotermes also differed in population density in the three areas, the first two genera being commonest in areas II and III, and Pseudacanthotermes in area I. A greater mean depth of occurrence in Pseudacanthotermes, and a negative frequency correlation with Microtermes, suggested that open areas provided fewer suitable nest sites for the former genus.

Population Ecology of Desert Rodent Communities: Habitats and Environmental Complexity

Article

Jul 1969

We investigated the relative densities of granivorous, nocturnal desert rodents in small plots within two arid regions of Arizona to study how sympatric species avoid competitive extinction. The most common rodents were kangaroo rats, Dipodomys spp., and pocket mice, Perognathus spp. We attempted correlating the density of each species with several environmental measurements, derived from the soil's i) depth; ii) texture or iii) resistance to sheer stress; or from the plant's i) species diversity; ii) growth forms or iii) foliage density. Successful variables were derived from plant growth form and foliage density. The soil's resistance to sheer stress also seemed important for a few species. In general, kangaroo rats were associated with sparseness of vegetation; pocket mice with denseness. One group of mice, which we term bush mice, seemed to require bushes and included two Perognathus spp., three Peromyscus spp., and probably a harvest mouse (Reithrodontomys fulvescens). Two other Perognathus spp. were taken in grassy habitats. Some suitable habitats tended to be complementary to others, suggesting that species associated with them are competitors. Comparisons of the density and distribution of D. merriami, present in both regions but under different biotic circumstances, reinforces the opinion that competition is responsible for the complementariness of habitats. In some cases the evidence suggests that competitive coexistence is accounted for by the fact that different specializations are needed to escape predation in different environments. We use variables which correlate with the relative density of various species to construct a model of habitat complexity. The rodent species diversities obtained in our plots can be approximately accounted for by this model. The model is based on the premises that the rodents collectively discriminate four qualities of soil surface, and three heights and two densities of vegetation. In general, specializations based on biotic variables appear most important.

Food and Feeding Relations of Three Species of Triturus (Amphibia Urodela) during the Aquatic Phases

Article

Jan 1968

R. A. Avery

The food in the stomachs of 525 Triturus cristatus, T. helveticus and T. vulgaris caught at two different ponds is listed. The diets of adult T. helveticus and T. vulgaris were similar, and comprised mostly the larvae and pupae of Diptera Nematocera, although a wide range of other aquatic invertebrates was taken. Adult T. cristatus ate the same food, and in addition large numbers of Asellus and Gastropoda. The tadpoles of all three species fed mainly on small Crustacea. It was concluded that each group selected the food most appropriate to its size.

A Comparative Study of the Ecology of Eight Species of Fenland Carabidae (Coleoptera)

Article

Jun 1965

Nancy Dawson

1. An ecological study was made at Wicken Fen, Cambridgeshire, of eight closely related species of carabid beetles: Agonum obscurum (Herbst), A. fuliginosum (Panz.), A. thoreyi Dej., A. viduum (Panz.), Feronia vernalis (Panz.), F. minor (Gyll), F. strenua (Panz.), and F. diligens Sturm. Differences were found in their summer microhabitats and in their winter hibernating places, and in the times in spring that they left their hibernating places and started to feed and later to lay eggs. The eight species also differed in the times in the autumn when they stopped feeding. 2. The young adults emerged from pupation during the autumn, and fed for a period. An analysis was made of the proportions of young to old adults in the winter populations of each species. This varied from species to species and differed in the two years. There was no evidence that individuals that had bred at least once had a shorter expectation of further life than the young adults that had not yet bred. All eight species were probably mainly scavengers and had a very varied diet. A comparison was made of the feeding habits of the three commonest species--Agonum obscurum, A. fuliginosum and Feronia diligens. There seemed little difference in the proportions of animal and plant food that they ate, or in the proportions of nine types of animal food (thrips, aphids, jassids, mites, spiders, harvestmen, Podura sp. (Collembola), Diptera, and Forcipomyia sp. larvae (Diptera)), or in the sizes of animal food as indicated by the sizes of Collembolan jaws and laciniae. Such differences as there were in the beetles' diet could be explained by their slightly different habitat preferences.

Habitat Overlap and Competitive Exclusion in Voles (Microtus)

Article

Oct 1968

A field study, designed to test the hypothesis that habitat segregation in sympatric populations of Microtus pennsylvanicus and M. montanus is due to competition, was conducted on the National Bison Range in western Montana between June 1961 and May 1962. Experimental reduction of the numbers of M. pennsylvanicus induced movements of M. montanus into the vacated habitat, forming the basis for acceptance of the hypothesis. The nature of the movements plus reciprocal avoidance behavior of both species of voles during normal circumstances suggest that the voles conform to the principle of competitive exclusion. The significance of niche overlap is stressed and its adaptive qualities are discussed.

The Temporal Component of Diversity Among Species of Birds

Article

Jun 1966

Robert E. Ricklefs

Data from 11 localities of wide geographic distribution indicate that the average length of the breeding season of individual species of birds occupies very nearly the same proportion of the total breeding season in all localities. This essentially eliminates a temporal component to increased tropical species diversity. Further analysis gives no evidence that closely related sympatric species stagger their nesting seasons to avoid competition, but in fact, the seasons of such pairs consistently overlap more than 90 per cent. This and other evidence indicates that the temporal diversity found within the total breeding season is the result of specific feeding differences together with temporal diversity in the availabilities of the different food resources. It also appears that the longer tropical breeding seasons differ from temperate ones only in having an expanded time scale; the relative position within the season and the portion used corresponding closely for pairs of similar tropical and temperate species. While differences in the timing of breeding cannot account for increased diversity, lower intensity of breeding caused by longer breeding cycles, smaller clutches, and lower nesting success may well reduce interspecific competition.

Ecology and Distribution of Pocket Gophers (Geomyidae) in Colorado

Article

Apr 1964

Richard S. Miller

The general distribution of the family geomyidae in North America is limited only by suitable soils, although a particular species may be also be limited by climatic or other factors associated with altitude and latitude and by interspecies competition. A study was made of the factors affecting the distributions of the pocket gophers Thomomys bottae, T. talpoides, Geomys bursarius, and Cratogeomys castanops in Colorado. The most critical factors in the relationships among pocket gophers are soil tolerance and competition. All four species in Colorado prefer deep light soils,but their ranges of tolerance vary, with the result that interspecies competition consists of the fundamental niche of one species being a proper subset of another. In each combination of competitive and is able to displace the other speices to less favorable habitats. The relationship among the four species in competitive ability is G. bursarius > C. castanops > T. bottae > T. talpoides. Possible mechanisms of competition are discussed in relation to body size, territory, aggression, and dispersal.

Overlap in Foods and Foraging of Four Species of Blackbirds in the Potholes of Central Washington

Article

Sep 1969

Overlap in foods and foraging of four species of breeding blackbirds in the Potholes of central Washington was estimated from samples of food delivered to the nestings obtained by the pipe-cleaner technique. Prey distribution and availability were sampled with emergence traps for aquatic species and by sweeping with a standard insect net for upland species. Overlap was estimated by the probability than an item of food drawn randomly from the diet of one species would be of the same prey category taken from the same habitat as an item drawn at random from the diet of another species. Because of the diurnal cycle of emergence of aquatic insects, overlaps were calculated for three periods of the day (preemergence, emergence and postemergence) and averaged for the final overlap value. The overall food overlap for three of the species is high for all periods of the day and there is little evidence for differential specialization within habitats. Habitat overlaps, however, are varied, being highest during the emergence period for Redwings and Yellowheads but highest during the afternoon between Redwings and Brewers. The total overlap values are very similar to the theoretical maximum values derived from competition theory by MacArthur and Levins.

A Niche Analysis of Colorado Ants

Article

Jan 1972

David C. Culver

Gregg's data on Colorado ants were examined in light of recent ecological theories. Predatory ants have high niche breadths and low niche overlaps as predicted by MacArthur and Pianka for searching predators that optimize the amount of food taken. Similar analyses were done for seed-eaters, slaves, and slave-makers.

A Multivariate Statistical Approach to the Hutchinsonian Niche: Bivalve Molluscs of Central Canada

Article

Jul 1971

Roger H Green

The use of multiple discriminant analysis to identify the significant and independent ecological factors separating species distributions is proposed and discussed. Such an analysis was performed on 345 samples, containing a total of 10 bivalve mollusc species, from 32 lakes in Manitoba, Ontario, and Saskatchewan. Measurements of nine ecological parameters were associated with each sample. Five discriminant functions account for 95% of the among species variance, and 4 of the 5 are ecologically interpretable. Three of these, accounting for 80% of the among-species variance, are interpreted as bases of trophic, rather than physical or chemical, separation. There is separation of species on each discriminant function. The use of dissatisfied scores to classify lakes with maximum relevance to species distributions is demonstrated and discussed. A generally applicable measure of environmental heterogeneity based upon this type of analysis is proposed. The value of this type of analysis in quantifying ecological concepts derived from the Hutchinsonian niche model is discussed. An example is given of a reduced available niche resulting in the loss of two species, smaller realized niches for the remaining species, and greater niche overlap.

Ecological Distribution in Anoline Lizards of Puerto Rico

Article

Oct 1964

A. Stanley Rand

The eight species of lizards of the genus Anolis in Puerto Rico can be divided into four morphological similarities. One, Anolis curvieri, is very different from the rest and has not been discussed here. The other seven species fall into three groups. Each of these groups occupies a different structural habitat which can be defined in terms of perch height and perch diameter. Within each of these three groups the species have very similar but not indential structural habitats but differ very widely in climatic habitat defined in terms of shade. Shade preferences seem to result from the temperature preferences of the species involved. In each group there is one species with high shade preference which is essentially restricted to the mountains. Each group also has a species with a lower shade preference which occurs in the lowlands and extends up into the mountains in exposed or sunny situations. One of the three groups has an additional species which is restricted to the hot and southwest corner of Puerto Rico. When one compares the temperature preferences or eccritic temperatures of the various species, one finds in each group that the highland species has a lower eccritic temperature than does the lowland species. There is little temperature difference between the lowland species and arid southwest species in the group where this additional third species is present. The species within each structural habitat show many morphological similarities which may be the result of their being closely related or may be the result of adaptation to similar environments. The differences in microhabitat between the Puerto Rican anoles separate them spatially though not completely. In species occupying different structural habitats in the same area the overlap may involve part of the home range of most of the individuals in the area. In species occupying the same structural but different climatic habitats the overlap may involve all of the home range of some individuals but of only a small fraction of the individuals in the total population. The spatial separation among Puerto Rican Anolis can be suggested to be of ecological significance because it reduces interspecific competition and because it allows the various species to adapt more precisely to different parts of the available habitat. Thus members of a genus may exploit the habitat more efficiently.

Resource Partioning in Ecological Communities

Abstract

No full-text available

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