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Predation: Direct and Indirect Impacts on Aquatic Communities
... Unfortunately, since 1984 when the survey was conducted in the Kakamega District, these forest fragments have been cleared at an alarming rate and converted to agriculture, and hence, the future survival of the snake populations is doubtful. Predation is a major ecological force influencing population dynamics, species distributions, and community structure (Kerfoot and Sih 1987) [14] . The most obvious direct effect of predation is the killing of prey, but a variety of indirect effects of predators on the behavior and life histories of prey and on dynamics at other trophic levels have been recognized (Kerfoot and Sih 1987) [14] . ...
... Unfortunately, since 1984 when the survey was conducted in the Kakamega District, these forest fragments have been cleared at an alarming rate and converted to agriculture, and hence, the future survival of the snake populations is doubtful. Predation is a major ecological force influencing population dynamics, species distributions, and community structure (Kerfoot and Sih 1987) [14] . The most obvious direct effect of predation is the killing of prey, but a variety of indirect effects of predators on the behavior and life histories of prey and on dynamics at other trophic levels have been recognized (Kerfoot and Sih 1987) [14] . ...
... Predation is a major ecological force influencing population dynamics, species distributions, and community structure (Kerfoot and Sih 1987) [14] . The most obvious direct effect of predation is the killing of prey, but a variety of indirect effects of predators on the behavior and life histories of prey and on dynamics at other trophic levels have been recognized (Kerfoot and Sih 1987) [14] . Thus, understanding predator-prey interactions is critical for management and conservation of species, and it relies in part on understanding the ecological and evolutionary processes at work. ...
Human historical experience with venomous snakes has probably shaped our responses to them. In African continent, where venomous snakes are common, most people consider all snake species to possess deadly venom and should be avoided. However, the focus of this survey was to exam the presence of snakes in Bertoua municipality. The research data collection was done by the use of check-sheets for a period of one month from 7:30am-5:30pm each day at the peripheral zone of the municipality. A random spot observation of 444 snakes was made on 6 species, black cobras (Naja melanoleuca), green mambas (Dendroaspis viridis), vipers (Bitis gabonica), green-tree snakes (Dendrelaphis punctulatus), small brown snakes (Dendrelaphis shokan), and python (Python regius). Ecological factors such as weather condition, vegetation, landscape, location, and day-period were also taken into account. The results of this study revealed that vegetation of the study area and weather condition have an association, χ 2 = 6.789 df=4, P<0.05. Additionally, vegetation showed a significant relationship on the snake species χ 2 = 13.158 df=10, P<0.05. Also, vegetation showed an association on the snake location, χ 2 = 6.910 df=2, P<0.05. Furthermore, vegetation revealed a significant relationship on day-periods, χ 2 = 12.221 df=4, P=0.016. Human encroachment into wildlife habitat due to population increase has been the main reason for human-wildlife conflict in Cameroon. Unsustainable crop-farming in most parts of Cameroon due to poverty resulting to shifting cultivation, a longstanding farming tradition believed to have destroyed the rainforest most. The presence of snakes in farmlands in Bertoua municipality might be partly due to a high snake population in the area, or the cropland harboring a high population of rodents, birds and amphibians preyed upon by snakes. Conflicts of this nature are expected to take a much heavy death toll on the snake population, either through direct killing or pesticides used on insect pest. The wildlife conservation stakeholders in Cameroon would need to educate local crop-farmers in Cameroon, especially in the Eastern Region on the management strategies of this kind of wildlife conflict.
... Predation is one of the most important processes influencing the diversity and structure of ecological communities (Sih et al. 1985, Kerfoot & Sih 1987, Chase et al. 2002, Barbosa & Castellanos 2005. The presence of predators can limit the possibility of single-species monopolies in prey assemblages, promoting species diversity at lower trophic levels (Paine 1966, Menge & Sutherland 1976). ...
Predation is a key ecological process regulating the structure and diversity of biological communities, yet predators do not exist homogeneously in nature. Coral reefs possess diverse assemblages of predatory fishes, the distribution and abundance of which is well documented for coastal and emergent reefs. However, for remote, isolated and submerged reefs, such as those found on pinnacles and seamounts, our understanding of predatory fish communities is limited. These features are ubiquitous in the world’s oceans and frequently targeted by fishers for their presumed fish aggregation properties. Here we describe communities of predatory fishes on a series of pinnacle reefs and contrast these to regional coastal and offshore emergent reefs. Pinnacles supported 2-4x higher abundance, biomass and diversity of predatory fishes compared to emergent reefs. They also supported unique communities, with 32 out of the 63 predator species in our study found only on pinnacle reefs. For species found on all three reef types, all were most abundant on pinnacles and the 6 taxa driving differences in community structure were most abundant on pinnacles. Together our results show predatory fishes are strongly attracted to pinnacles, although the mechanisms are still unclear. Prioritising the selection of these small ecological magnets in conservation planning would be an effective approach to target the protection of regional reef fish biodiversity.
... Eventually, interactions within and among populations with physiological niche shifts will influence the whole fish community. An abiotic and biotic interaction influences fish community structure directly (Kerfoot and Sih, 1987;Strauss, 1991). In present study, different environmental factors exert influence at different level of physiological interactions (Table 1). ...
Ecosystem dynamics undergoing alterations in structure and function highlights the need to look into the relations between ecological parameters and organismal fitness and tolerance. Ecophysiological studies are used to understand how organisms adapt to and cope up with environmental stress. Current study uses a process-based approach to model physiochemical parameters regarding seven different fish species. Species respond to climatic variations via acclimation or adaptation through physiological plasticity. Four sites are differentiated into two types based on the water quality parameters and metal contamination. Seven fish species are clustered into two groups, each group depicting separate pattern of response in similar habitat. In this manner, biomarkers from three different physiological axes- stress, reproduction, and neurology were taken to determine the organism's ecological niche. Cortisol, Testosterone, Estradiol, and AChE are the signature molecules estimated for the said physiological axes. The ordination technique, nonmetric multidimensional scaling, has been utilized to visualize the differentiated physiological response to changing environmental conditions. Then, Bayesian Model Averaging (BMA) was used to identify the factors that play a key role in refining the stress physiology and determining the niche. Current study confirms different species belonging to similar habitats respond to various environmental and physiological factors in a different manner as various biomarkers respond in a species-specific pattern that induces the choice of habitat preference controlling its ecophysiological niche. In the present study, it is quite apparent that adaptive mechanism of fish to environmental stress is achieved through modification of physiological mechanisms through a panel of biochemical markers. These markers organize a cascade of physiological event at various levels including reproduction.
... Predation (De Meester et al., 1998) and competition (Manca & de Bernardi, 1985) affect the diversity, abundance and certain aspects of the life history of cladocerans. For example, the presence of predators can determinate the duration or age at maturity of their prey (Kerfoot & Sih, 1987), while species more vulnerable to predation invest more in reproduction than less vulnerable species. Anthropic influences, however, also exist-such as the current global warming (Yurista, 1999), acidification (Zimmer & Storr, 1984) or salinization (Anton-Pardo & Armengol, 2012)-that affect zooplankton diversity, behaviour, body size, abundances, and-in the pelagic populations in temperate regions-the age at maturity (McKee et al., 2002). ...
Zooplankton play a key role in aquatic ecosystems constituting an essential intermediate component in aquatic food webs. Cladocerans in particular are widely studied as model of generalist filter feeders. At the regional level, the cladoceran Daphnia spinulata is found in numerous habitats with wide conductivity range (160 μS cm ⁻¹ to 14.000 μS cm ⁻¹ ), but information about the species's tolerance range or life history is scarce. Our objective was to generate essential information about D. spinulata ' s life history and the main parameters related to two contrasting salinity levels representative of water bodies of the pampean plain. Results obtained in laboratory bioassays showed that individuals at low conductivity (700 μS cm ⁻¹ ) had more moults, a lower mortality and a higher life expectancy at birth, a higher generation time, and an earlier peak density than those at high‐conductivity treatments (5000 μS cm ⁻¹ ). The maximum density reached was similar for both conductivities indicating a similar growth capability attained by different strategies. Moreover, the results indicated that D. spinulata at different conductivities was able to reproduce, with the offspring thus contributing to population growth. This study provided a knowledge of the life history strategies of this endemic cladoceran at two different conductivities, thus generating crucial information on the population dynamics and for evaluating the species's role as a possible salinity indicator in pampean water bodies. Nevertheless, future investigations will be necessary in order to identify the absolute limits of tolerance and the optimum conductivity for this species and determinate which stressors will act as a mictic stimuli.
... Natural populations of herbivorous zooplankton like D. magna are subjected to feeding pressure by both vertebrate (fish) and invertebrate predators (Kerfoot and Sih 1989). Only their extremely high population growth rates (enabled by their parthenogenetic reproduction) and adaptive behavioural responses allow them to compensate the high mortality rates caused by predation and sustain viable populations despite massive predation losses (Boersma et al. 1998). ...
Lipids and fatty acids are key dietary components for the nutrition of organisms at all trophic levels. They are required to build cellular structures, such as cell membranes, serve as energy storage and are taking part in signal transduction cascades. For decades, ecological research investigated how dietary fatty acid availability contributes to the fitness of individuals and their populations. The omega-3 polyunsaturated fatty acid eicosapentaenoic acid (EPA) found particular interest, as its dietary availability determines the fitness of many aquatic consumers. Due to the small body size of zooplankton, only bulk tissue fatty acid analysis was so far performed and thus the tissue-specific importance of EPA for zooplankton remained elusive. Here we used matrix-assisted laser desorption ionization – mass spectrometry imaging (MALDI-MSI) to reveal the tissue-specific distribution of functional phospholipids in the herbivorous zooplankton Daphnia magna. We demonstrate several lipid species for heart, eggs, gut, gonads, somatic and neurological tissues of D. magna, including the compound eye, as well as the optical and cerebral ganglion. The compound eye revealed a large diversity in EPA-containing lipid species, which were also found in other neurological tissues and the eggs. Such knowledge of tissue-specific fatty acid requirements is essential to investigate how selective allocation of dietary fatty acids within this key grazer on a functional and molecular level affects processes from the individual to food web scales. This methodological advancement will allow investigations on how invertebrates’ physiology and behaviour adjust to changing environmental conditions and potentially affect food web structures including the trophic transfer of dietary fatty acids.
... Interactions between predators and prey help shape the food web and community structure [1][2][3]. The body sizes of predator and prey strongly mediate these interactions [4][5][6]. ...
Invasive predators pose a critical threat to native taxa. Body size plays an important role in mediating the interactions of predator and prey. For piscivorous fishes, increased predator body size can be accompanied by the selection of increasingly larger prey or may reflect a mix of small and large prey. Knowledge of such interactions helps determine how predation affects population vital rates. Here, we assessed the predatory effects of invasive Brown Trout (Salmo trutta) on populations of native Rio Grande Sucker (Catostomus plebeius) and Rio Grande Chub (Gila pandora) in streams of the Jemez River watershed (New Mexico, USA). Trout diets were sampled every two weeks during the 2020 growing season. Predator and prey body lengths were measured to examine relationships to better understand patterns of piscivory and quantify the threat Brown Trout pose to populations of Rio Grande Chub and Rio Grande Sucker. Across all streams and sampling dates, 7% of Brown Trout diets contained fish. Predator–prey length relationships reflected a ‘wedge’ pattern, indicating that Brown Trout consumed an increasing range of prey body sizes as they grew larger. Rio Grande Sucker and Rio Grande Chub comprised 46% of consumed fishes. The findings demonstrated that Rio Grande Sucker and Rio Grande Chub experience constant predation over the growing season by Brown Trout. Moreover, our study provides evidence that these invasive predators pose a threat to the viability of Rio Grande Chub and Rio Grande Sucker populations. Conservation efforts to protect these chub and sucker populations must account for and directly address predation by invasive Brown Trout.
... Similarly, Drummond-Davis et al. (1982) found that P. acadianus is the most frequently consumed prey by rock crabs in kelp beds in Nova Scotia. Although more food is available in farm sites (e.g., fallen mussels, associated organisms), small hermit crabs may avoid such areas since predation risks are elevated, illustrating a behavior defined by Kerfoot and Sih (1987) whereby aquatic prey adjust to spatial and temporal variation in predation risk. ...
Mussel farming influences benthic environments by organic loading and the addition of physical structure within aquaculture leases. This study evaluated near-field (distance to mussel aquaculture structures, line-scale) and bay-scale (inside vs. outside a blue mussel, Mytilius edulis, farm) effects of an offshore mussel farm in Îles de la Madeleine (Canada) on epibenthic macrofaunal communities. Benthic communities were evaluated by underwater visual counts using SCUBA in June and July 2014. The mussel farm influenced benthic communities at line-and bay-scales. Overall, crabs (Cancer irroratus, Pagarus pubecsens, Pagarus acadianus), sea stars (Asterias rubens), Northern moon snails (Polinices heros), and American lobsters (Homarus americanus) were more abundant in farm sites than outside of farm sites and ocean quahogs (Arctica islandica) were more abundant outside. No clear spatial trend was observed for winter flounder (Pseudopleuronectes americanus) and the sand dollar (Echinarachnius parma) but both species differed (flounder) or showed a trend to differ (sand dollar) between sampling dates. Spatial structure in the distribution of macrofauna was evident within the aquaculture lease as most species were more abundant directly below and close to mussel lines and anchor blocks. There was no spatial structure in non-farm sites. Further investigation is needed to evaluate if mussel farms serve as ecological traps for the species that congregate within them. The long-term effects of the observed spatial effects of offshore mussel culture on macrofauna fitness remains unknown.
... Excessive sedimentation may also impact egg survival by limiting the amount of available oxygen in the water column and increasing biological oxygen demand (Edwards et al., 2005;Gatch et al., 2020). Additionally, successful spawning sites may protect eggs from predatory fishes via interstitial spaces, as aggregations of incubating eggs can suffer high levels of mortality if exposed (Kerfoot and Sih, 1984;Roseman et al., 2006). ...
Saginaw Bay is a shallow, nutrient-rich embayment in Lake Huron that historically had a complex network of natural rocky reefs. These reef habitats were used as spawning and nursery areas for a variety of fish species, but decades of land-use related sedimentation caused many of these reefs to be degraded. Our study objectives were to analyze abiotic and biotic conditions on degraded and remnant reefs and describe spawning patterns of walleye (Sander vitreus) and lake whitefish (Coregonus clupeaformis) at these sites to determine the potential for increased utilization following reef restoration. During fall and spring 2014–2016, we evaluated water quality and egg predation at four sites with varying levels of reef degradation. Further, we documented reproductive utilization through capture of spawning adults and quantification of egg deposition. Walleye and lake whitefish utilized multiple sites for reproduction; however, densities of spawners and deposited eggs were low, suggesting that they were not utilizing study sites as major spawning locations. Walleye and lake whitefish eggs were eaten by multiple fish species, including larger fish such as channel catfish (Ictalurus punctatus). Dissolved oxygen levels were adequate (i.e., >7 mg 02 L⁻¹) during spring walleye egg incubation; however, bottom dissolved oxygen levels became very low at some sites during winter ice cover, coinciding with lake whitefish egg incubation. As restoration of rocky reefs proceeds in the Bay, evidence of remnant reef spawning fish bodes well for long-term success, though potential limiting factors such as low dissolved oxygen, sedimentation, and egg predation require continued monitoring.
... Predation is a fundamental top-down force that shapes life history, population dynamics, and community structure (Kerfoot andSih 1987, Wellborn et al. 1996). Prey utilize a bewildering array of mechanisms to avoid predation (Edmunds 1974, Ruxton et al. 2004, and organisms lacking morphological or chemical defenses often use behavioral mechanisms, such as flocking, mobbing, group vigilance, reduced activity, and spatial or temporal habitat shifts (avoidance), to coexist with predators (Lima andDill 1990, Lima 1998). ...
Avoiding detection is perhaps the ultimate weapon for both predators and prey. Chemosensory detection of predators via waterborne or airborne cues (predator-released kairomones) is a key prey adaptation in aquatic ecosystems. Pirate perch, Aphredoderus sayanus, a largely insectivorous mesopredatory fish, are considered to be chemically camouflaged because they are unavoided by all colonizing organisms tested, including treefrogs and aquatic insects, despite stronger predatory effects on target taxa than several avoided fish. To address the mechanism behind camouflage we used aquatic insect colonization as a bioassay to test 1) whether increasing pirate perch density/biomass leads to increased avoidance, and 2) whether pirate perch mask heterospecific fish kairomones. Insect abundances, species richness, and community structure showed no response to pirate perch density. Lastly, pirate perch did not mask the kairomones of heterospecific predatory fish. Results support the idea that fish kairomones are species-specific, and chemical camouflage is driven by a unique chemical signature that is either undetectable or has no negative associations for colonizers.
... Cooke and Philipp (2004) found that the short-term (24h) post-release mortality of bonefish could be as high as 40% and was dependent on the abundance of predators in the area of the tagging event. Predation is a natural occurrence and an important mediator of community interactions in aquatic ecosystems (Kerfoot and Sih, 1987). Animals released in poor condition are at an elevated risk of predation until they recover from capturecaused exhaustion (Raby et al., 2014). ...
Due to their highly migratory nature, the management of tuna stocks is done at the global ocean scale to the detriment of local management specific to each country. Regional fisheries management organizations (RFMOs) such as the Commission for the Conservation of Atlantic Tunas (ICCAT) have been created in each ocean to coordinate fishing statistics among fishing countries and stock assessment work. As the first tuna port in West Africa, Côte d'Ivoire is witnessing intensive exploitation, of the three main species of tropical tunas (yellowfin, skipjack and bigeye) present in the waters of its EEZ by industrial offshore fleets of different nationalities. By definition, stock assessments are carried out at the Atlantic Ocean scale by ICCAT and little information is produced to characterize the dynamics of local abundance over time and to measure the consequences of the state of exploitation of the stocks on this local resource. An approach based on the estimation and characterization of the fluctuations of the local tuna resource is necessary, and this cannot be done without a good understanding of the local and global factors that condition the presence of the species in the Ivorian EEZ and their migratory behaviour with the rest of the Eastern Atlantic. This thesis is part of a general context of the management relationship from global to local known as "glocalization".
To achieve these objectives, we estimated the local tropical tuna resource of the Côte d'Ivoire EEZ using a seasonal spatio-temporal model (VAST) developed by Thorson et al. (2020a) applied to European (Spain and French) purse seiners CPUE operating under fishing agreements in this area . The indices relating to the abundance of this local resource allowed the characterization of its seasonal and interannual dynamics over a 20-year study period. The results suggest two seasons of tuna abundance in the Ivory Coast EEZ: a peak of large yellowfin on free schools between April and May and a peak of skipjack under FADs between September and November. Furthermore, the analysis of the migration phenology through the Côte d'Ivoire EEZ highlights the arrival of large yellowfin tuna on free schools from February onwards. We then studied the relationship between the local abundance fluctuations of the different species and some internal (environmental conditions) and external (level of abundance and global exploitation) factors to the study zone. By highlighting the dependence of local resource fluctuations on both local and global factors (using wavelet analysis and the 'convergent cross mapping' method of Sihugara et al. (2012)), we deduced that the global stock's state conditions the abundance of tuna resources in the Ivorian EEZ. Thus, this study reinforces the idea of combining global management measures with local measures ('glocalization') to optimize the management of the local tuna resources of Côte d'Ivoire's EEZ, with potential application to the local tuna resources of other coastal countries of the Atlantic Ocean.
In addition, the Atlantic Tropical Tuna Tagging Programme (AOTTP) provided an opportunity to actively participate, in parallel to the main objective of this thesis, in the estimation of some parameters characterizing the uncertainties associated (estimates reporting rate, analysis of the effects of tagging conditions on recovery rates) with catch-recapture data. Therefore, this component should be seen as an overview of the local implications and contributions to research programmes conducted at global scales and as a prerequisite for a successful "glocalized" tuna fisheries management. This glocalised management, i.e. combining the objective of global management with the optimisation of coastal countries' profits, would allow integrating the specificities of coastal EEZs into the implementation of stock regulation measures in exchange for better participation of coastal countries in the collection and analysis of tuna fisheries data.
... Predation is well known to affect the distribution, abundance, and behavior of prey (Kerfoot and Sih 1987). Here, we documented changes in the population dynamics of two species of pondbreeding frogs in response to a change in the fish predator community. ...
Predation can affect prey behavior, demography, abundance, and distribution, particularly in lentic freshwater ecosystems. Fish are predators known to reduce the abundance of their prey and to restrict the distribution of species. Using time series which spanned 43 and 22 yr, respectively, we analyzed the effect of a change in the fish predator community on the dynamics of two pond‐breeding amphibian populations (Rana temporaria and Rana dalmatina). Specifically, we used a state‐space time series model which allows for density dependence and observation error, to ask whether the change in predation risk affects population growth rate and the return point around which the populations fluctuate. The results showed that the type of observation error assumed did not affect the biological parameters. We found evidence for density dependence in both populations. The effect of the change in fish predation on population growth rate and the return point was strong in the population where fish invaded a previously fish‐free pond. The effect was weaker in the population where the change was from cyprinid fish to pike. The results showed that fish predation can have strong effects on amphibian population dynamics. The observed population dynamical pattern is phenomenologically similar to alternative stable states.
... Interactions between prey and predators are amongst the major selective forces that drive a diverse suite of functional phenotypes in both counterparts (Kerfoot andSih 1987, Tollrian andHarvell 1999). Feeding relationships can indeed shape elaborate behavioural, physiological and morphological adaptations to prevail in the evolutionary arms race (Edmunds 1974, Surlykke and Miller 1985, Reimchen 1980, West et al. 1991, Brodie III and Brodie Jr et al. 1999, as well as have a prominent and pervasive impact on the stability of food webs, on the structure of animal communities 2 and on the dynamics of natural populations (Emmerson and Raffaelli 2004, Brose et al. 2006b, Petchey and Dunne 2012. ...
Predator–prey interactions are amongst the strongest selective forces that promote the evolution of local phenotypes in both predators and prey. However, intraspecific spatial
covariation in phenotypic traits between predators and prey has been rarely investigated,
especially at a large geographic scale. Here, we studied the covariation between
prey composition and some phenotypic traits, such as wing length, bill length and
plumage colour, of a widely-distributed nocturnal predator, the western barn owl Tyto
alba. By using 3100 specimens collected across its entire range of distribution, spanning
from Europe to Middle East and Africa, we showed that wing length positively
covaries with prey size, but not with taxonomic composition. This finding suggests that
larger prey might have selected for larger body size and/or that larger individuals might
be more selective in hunting large prey. In addition, we also found that paler-plumaged
populations generally hunt larger prey. Paler barn owls might be thus better specialized
in capturing averagely larger prey and/or mainly hunt in habitats where larger
prey are more abundant. In addition, considering that paler individuals are generally
larger than brownish ones, it is possible that paler plumage colour might have evolved
as a by-product of selection towards a large body size, which in turn have emerged in
response to prey size composition. However, irrespectively of the direction of causality
and the phenotypic target of selection, we showed that predator–prey interactions can
affect spatial phenotypic variation by promoting the evolution of local adaptations.
... From an evolutionary perspective, the "slow" behavior is related to antipredator actions and fixed behaviors [sensu Sih, (1987)], including reduced foraging. During rearing of E. abjecta larvae, we perceived a different behavior model that includes extremely low activity in all instars (93.8% of the time for most larvae) but high predation intensity, with the consumption of up to 19 prey items per day. ...
Understanding the life cycle of Neotropical odonate species is essential given our scant knowledge of this region. In this paper, we examine growth ratio between instars, development patterns, and active/passive feeding behavior of the Andean dragonfly Erythrodiplax abjecta (Rambur, 1842). Larvae were obtained from eggs laid by two females in the laboratory and were maintained at 12–34 °C in individual containers until either their emergence or their death. Larvae hatched 26–57 days after laying, and the total development time was determined as being 316 (SD ±6.6) days, including 13 instars. Larval instars were characterized using six morphometric variables. The foraging behavior was analyzed considering the time of day and the percentage of the background covered by detritus. The growth ratios between successive instars averaged 1.9 for FW pad length, 1.6 for HW pad length and 1.2 for head width, head length, metathoracic leg length, and total length. Neither the active foraging nor the sit-and-wait foraging behavior were affected by either time of the day or the percentage of background covered by detritus. Erythrodiplax abjecta is univoltine and has a slow lifestyle associated with lentic perennial waters, where larval development and growth rates are low. We provide an equation to estimate the E. abjecta larval instars from field specimens.
Given that our results were obtained from the eggs laid by only two females, further studies including a larger sample size are needed to validate their generality.
... Predation at the juvenile life stage can structure populations by selectively influencing which individuals survive to adulthood (Nielsen 1980;Rice et al. 1993). Thus, identifying the mechanisms by which individuals experience differential predation as juveniles is important for understanding how predation processes influence populations and the community structure observed at the adult stage (Kerfoot and Sih 1987;Rice et al. 1997). Our results suggest that a potential mechanism by which sympatric crappie populations are structured is habitat-linked vulnerability to predation. ...
Black Crappie Pomoxis nigromaculatus and White Crappie Pomoxis annularis have contrasting patterns of performance along a gradient of turbidity for reasons that have yet to be elucidated. We examined how distinct, habitat‐linked morphologies of these congeners make Black Crappie more specialized for structurally complex vegetation and White Crappie more specialized for open water habitats, and tested how these interspecific differences during early life influence their vulnerability to predation within open water and vegetated habitats. Juvenile Black Crappie had deeper bodies with a short, deep caudal peduncle and juvenile White Crappie had more fusiform bodies with an elongated caudal peduncle. These morphological differences had important consequences for predator evasiveness in each habitat, where Black Crappie were more successful at evading capture in vegetation and White Crappie were more successful at evading capture in open water. Because turbid lakes rarely support vegetation and clear lakes are heavily vegetated, our results suggest that differential success observed between these congeners may be better explained by adaptations to structural habitat complexity rather than tolerance to turbidity. Our study supports that habitat‐linked morphological variation is critically important for predator evasiveness and can structure populations across species distributions.
... Predation is a major structuring force in populations and communities (Kerfoot and Sih, 1987;Terborgh and Estes, 2010). Epibenthic predation, such as fish feeding on infauna, is common and influences the infaunal communities in estuaries (Virnstein, 1977;West et al., 2003;Tomiyama et al., 2007). ...
Behavioral responses of infauna to predation have received limited study, especially in varying hydrodynamic conditions above estuarine sediments. Many estuaries also are impacted by chemical pollution, including runoff of terrestrial insecticides such as chlorpyrifos. We tested how feeding behaviors of a tube-dwelling, interface-feeding worm, Polydora cornuta, change due to predation by an omnivorous estuarine fish, Fundulus parvipinnis, in the contexts of hydrodynamic regime and sub-lethal exposure to chlorpyrifos. We performed two experiments in a laboratory flume at two flow speeds (6 or 15 cm s −1). We analyzed feeding behaviors of P. cornuta when F. parvipinnis were either actively feeding on the worms, caged upstream to prevent predation, or absent from the flume. In our first experiment, the presence of actively feeding F. parvipinnis reduced the time P. cornuta spent feeding by half relative to when fish were absent. Fish caged upstream had no effect on worms' feeding activity, indicating that P. cornuta reduced their feeding in response to tactile stimuli or sensing light shadows, rather than chemical alarm cues. Our second experiment tested the effects of actively feeding F. parvipinnis on the feeding behaviors of P. cornuta that had undergone a 96-h exposure to chlorpyrifos. Worms exposed to chlor-pyrifos reduced feeding relative to unexposed worms, but only in the absence of predatory fish. Flow speed also influenced worms' behavior, with worms preferentially suspension feeding at the faster flow. In both experiments , individual worms that were observed to be attacked by F. parvipinnis resumed feeding approximately 10-11 min after the attack. The combined results demonstrate that the close proximity of actively feeding fish has a consistently greater effect on the feeding behavior of an infaunal polychaete than does sub-lethal exposure to a toxicant or variation in water flow.
... Invertebrate predation by Chaoborus is considered a strong biotic factor controlling the SDC abundance in our conceptual model (Fig. 14.1). Indeed, Chaoborus is well known as an active predator that reacts to prey movement and can easily suppress both the active planktonic cyclopoids and the diapausing cyclopoids, as well as most other invertebrates in deep waters and sediments (Kerfoot and Sih 1987;Hanazato and Yasuno 1989;Arnott and Vanni 1993;Pinel-Alloul 1995a, b). Chaoborus may recognize diapausing cyclopoids as prey in the anoxic zone of sediments due to their different torpidity during diapause and their reaction to tactile contact (Elgmork 1996). ...
Cyclopoid copepods are a dominant component of freshwater zooplankton and the Cyclopidae is the most diverse family. Dormancy is a fundamental process of cyclopoid life history in permanent lakes and temporary ponds. In boreal lakes, cyclopoid diapause has been documented mainly in Northern Europe but more rarely in Northern America. We present the first assessment on summer diapausing cyclopoids (SDC) in 22 boreal lakes in southern Québec, which vary in their morphometry, tropic status, and predation pressure by fish or invertebrates. We developed a conceptual model to test the hypothesis that diapausing patterns of SDC in boreal lakes are a complex response depending primarily on morphometric and trophic features and secondly on the intensity of hypolimnetic anoxia and predation by fish or invertebrates. Using morphometric indices, lakes were classified in groups varying by the importance of wind-mixing, the strength of thermal stratification during summer, the potential of meromixis, and the risk of predation by fish or chaoborids. Three cyclopoid species (Diacyclops thomasi, Cyclops scutifer, Mesocyclops edax) dominated in all groups of lakes, while Diacyclops nanus and Acanthocyclops vernalis were found in small abundance and only in few lakes. The highest abundances of SDC (density and biomass) were found in sediments of thermally stratified mesotrophic lakes with intermediate wind-mixing index (Ko) and low potential for meromixis (Pm). Strong positive correlations were found between SDC and meiobenthos abundances in all groups of lakes. High biomass of Chaoborus larvae or presence of large populations of fish negatively affected SDC abundances in meiobenthos. Morphometric features, wind-mixing and thermal stratification, as well as the abundance of Chaoborus and fish predators are the key factors governing species diversity and abundance of summer diapausing cyclopoids in boreal lakes.
... Predator-prey interactions influence the distribution and abundance of freshwater species (Kerfoot & Sih, 1987). Habitat characteristics and the physical-chemical environment (Crowder & Cooper, 1979;Crowder et al., 1981) affect the outcome of these interactions, which are ultimately a determining factor in the structure of aquatic communities (Carpenter et al., 1985;Beauchamp et al., 2007). ...
Foraging characteristics of siscowet lake trout (Salvelinus namaycush siscowet) on deepwater sculpin (Myoxocephalus thompsonii) were studied under ecologically relevant downwelling light intensities (9.0 × 108 to 1.62 × 1011 photons m−2 s−1) and emission spectrum (500–510 nm) on varying substrates (gravel, sand, and black fabric). Siscowet reaction distance within our trials increased with light intensity up to 6.0 × 109 photons m−2 s−1, after which reaction distance remained constant with additional increases in light intensity following the Michaelis–Menten saturation function. Reaction distances were not affected by substrate type under any light intensity. The number of prey captures also increased with increasing light intensity, with most orientations toward prey occurring within the siscowet’s forward sector (± 0°–60°, where 0° represents the tip of the siscowet rostrum). Finally, the overall probability of prey capture was positively related to reaction distance at each light intensity. Results suggest that siscowet can visually forage on benthic prey at great depth in Lake Superior, and reaction distance (≤ 27 cm) to sculpin may not diminish until depths exceed 200 m (6.00 × 109 photons m−2 s−1).
... They participate in the cycling of matter and energy flux by eliminating plankton algal cells from water depths (Mayer et al., 1997;Dodson et al., 2000). In turn, they serve as food for all fish species at the early ontogenetic development stage (Kerfoot and Sih, 1987;Sutela and Huusko, 2000). Zooplankton are characterized by short life cycles and fast adaptation to environmental changes. ...
The aim of this study was to determine the structure of zooplankton in three artificial water reservoirs, the technological function of which is to pre-treat waters from a drainage system of a brown coal open mine by removing inorganic suspension. The background for the zooplankton qualitative and quantitative analyses was the hydrochemical conditions in the individual reservoirs. The greatest zooplankton abundance ( N ), number of taxa ( n ), Shannon’s diversity ( H' ), and species eveness ( J' ) was noted in reservoir Chabielice ( N mean = 1311 ind. L ⁻¹ , n = 26, H' = 2.09, J' = 0.64) which was dominated by eurytopic Rotifera species ( Keratella cochlearis , Keratella tecta , Keratella valga , Polyarthra longiremis , Filinia longiseta ). Their abundance was positively correlated with water pH and nutrient concentrations. Reservoir Kamień was characterized by the highest mean values of total suspension (9.6 mg L ⁻¹ ), chlorophyll a (Chl a ) content (10.4 μg L ⁻¹ ), and water temperature (20.0 °C). These factors significantly correlated with crustacean biomass. The thermal-oxygenation conditions, low trophic level, and low productivity of the water (Chl a = 5.4 μg L ⁻¹ ) in reservoir Północny determined the overall low zooplankton abundance ( N mean = 153 ind. L ⁻¹ ). Artificial water bodies of opencast mine drainage systems are biologically unstable, but they do have some characteristics of natural ecosystems, and they do take over their functions. Zooplankton is an indicator of their ecological functionality. Knowledge gained about such reservoirs could contribute to decision-making about strategies for water reclamation and how to manage it.
... The strong predator-prey interactions between zooplankton and planktivorous fish in homogenous pelagic communities have been well-described (Brooks & Dodson, 1965;Kerfoot & Sih, 1987;Bollens & Frost, 1991). Those studies also showed that zooplankton migrate vertically in the water column to avoid predation by planktivorous fish (Gliwicz, 1986;Bollens & Frost, 1991;Easton & Gophen, 2003). ...
The distribution pattern of benthic meiofauna in freshwater ecosystems reflects a trade-off between residences in the high-risk, but productive, sediment surface versus the safer, but physiologically harsher, conditions deeper in the sediment. In this study, we used field enclosures and exclosures in a natural freshwater pond to investigate the effects of the juvenile common carp (Cyprinus carpio) on the distribution patterns of meiofaunal assemblages. Carp fed voraciously on meiofauna, reducing within few days the density and biomass of nematodes, oligochaetes, and microcrustaceans but not of rotifers, in the upper (0–2 cm) as well as deeper (2–4 cm) sediment layers. However, fish predation had less impact on the populations of nematodes and oligochaetes in the deeper sediment than in the surface sediment, as evidenced by reductions of 65 versus 80%, respectively. An analysis of the gut contents of carp indicated a high degree of omnivory, including the frequent consumption of meiofaunal organisms and also demonstrated the importance of meiobenthic invertebrates as prey for juvenile bottom-feeding fishes.
... Although cascading effects of predators can influence basal resources, prey population dynamics, and community structure (Kerfoot andSih 1987, Terborgh andEstes 2010), the mechanisms of these effects are often poorly understood. Classic trophic cascades that were assumed to be generated by predator consumption (density-mediated indirect interactions; DMIIs) may actually be driven by predators scaring and changing the behavior of their prey (trait-mediated indirect interactions; TMIIs; Abrams 1995, Preisser et al. 2005, Peckarsky et al. 2008, Long and Hay 2012. ...
... The presence (and identity) of predators is an important component of patch quality, and predators can have a variety of effects on species diversity and community structure (Paine 1966, Kerfoot and Sih 1987, Wellborn et al. 1996, Crooks and Soule 1999, Terborgh et al. 1999, Prugh et al. 2009, Estes et al. 2011. For example, the transition from fish to fishless habitats is a defining characteristic for freshwater communities (Wellborn et al. 1996). ...
Two of the most important factors determining community structure and diversity within and among habitat patches are patch size and patch quality. Despite the importance of patch size in existing paradigms in island biogeography, metapopulation biology, landscape ecology, and metacommunity ecology, and growing conservation concerns with habitat fragmentation, there has been little investigation into how patch size interacts with patch quality. We crossed three levels of patch size (1.13 m2, 2.54 m2 and 5.73 m2) with two levels of patch quality [fish presence/absence - green sunfish (Lepomis cyanellus) and golden shiners (Notemigonus chrysoleucus) in 6 replicate experimental landscapes (3 x 2 x 6 = 36 patches). Both fish predators have been previously shown to elicit avoidance in ovipositing treefrogs. We examined how patch size and patch quality, as well as the interaction between size and quality, affected female oviposition preference and male calling site choice in a natural population of treefrogs (Hyla chrysoscelis). Females almost exclusively oviposited in the largest fishless patches, indicating that females use both risk, in the form of fish predators, and size itself, as components of patch quality. Females routinely use much smaller natural and experimental patches, suggesting that the responses to patch size are highly context dependent. Responses to fish were unaffected by patch size. Male responses largely mimicked those of females, but did not drive female oviposition. We suggest that patch size itself functions as another aspect of patch quality for Hyla chrysoscelis, and serves as another niche dimension across which species may behaviorally sort in natural systems. Because of strong, shared avoidance of fish (as well as other predators), among many colonizing taxa, patch size may be a critical factor in species sorting and processes of community assembly in freshwater habitats, allowing species to behaviorally segregate along gradients of patch size in fishless ponds. Conversely, lack of variation in patch size may concentrate colonization activity, leading to intensification of species interactions and/or increased use of lesser quality patches. This article is protected by copyright. All rights reserved.
... Water flow is unquestionably a critical factor influencing the structure and function of freshwater and marine ecosystems (e.g., Snelgrove and Butman 1994;Hart and Finelli 1999). Predation also has been widely documented as a key process affecting aquatic populations and communities (e.g., Paine 1966;Kerfoot and Sih 1987;Terborgh and Estes 2010), and fishes are among the most common aquatic predators. Although the swimming performance of fishes has been widely studied in relation to water velocity and turbulence (e.g., Plaut 2001;Johansen et al. 2007;Liao 2007), research into how hydrodynamic conditions influence predation by fishes has been relatively limited. ...
... Adaptations to predation by aquatic organisms include morphological and chemical defenses, modified behavior, and life-history modifications (Kerfoot and Sih, 1987). The study of predation using freshwater snails as a model has been instructive due to multiple predators that specialize on freshwater snails and influence populations, and the large variation in body size and degree of shell development (Rundle and Brönmark, 2001). ...
... Ecological selection against hybrids may arise via mismatches between hybrid phenotypes and e.g. the environment or demands for anti-predator capacities, yet direct predation costs to hybridization in the wild remain inconclusive. Predation is a ubiquitous and powerful ecological agent of natural selection [7][8][9] that may act as an extrinsic, postzygotic reproductive isolation barrier if invoking hybrid inviability [1]. If hybrids have intermediate phenotypes that fall between adaptive peaks occupied by parental species [10] hybrids may be removed by selection [11]. ...
Species integrity can be challenged, and even eroded, if closely related species can hybridize and produce fertile offspring of comparable fitness to that of parental species. The maintenance of newly diverged or closely related species therefore hinges on the establishment and effectiveness of pre-and/or post-zygotic reproductive barriers. Ecological selection, including predation, is often presumed to contribute to reduced hybrid fitness, but field evidence for a predation cost to hybridization remains elusive. Here we provide proof-of-concept for predation on hybrids being a postzygotic barrier to gene flow in the wild. Cyprinid fishes commonly produce fertile, viable hybrid offspring and therefore make excellent study organisms to investigate ecological costs to hybrids. We electronically tagged two freshwater cyprinid fish species (roach Rutilus rutilus and bream Abramis brama) and their hybrids in 2005. Tagged fish were returned to their lake of origin, exposing them to natural pre-dation risk from apex avian predators (great cormorant, Phalacrocorax carbo). Scanning for regurgitated tags under cormorant roosts 3–4 years later identified cormorant-killed individual fish and allowed us to directly test for a predation cost to hybrids in the wild. Hybrid individuals were found significantly more susceptible to cormorant predation than individuals from either parental species. Such ecological selection against hybrids contributes to species integrity, and can enhance species diversification.
... Although the diets of invasive and native consumers may overlap, sharing a resource does not necessitate competition. Through indirect pathways, the effect of one species on another can be positive, negative, or null depending on how shared prey respond either behaviourally or numerically (Kerfoot & Sih, 1987;Preisser, Bolnick, & Benard, 2005;Werner & Peacor, 2003). For instance, the threat of a predator can shift prey distributions into adjacent habitats, thereby indirectly increasing prey availability for other predators (Burks, Lodge, Jeppesen, & Lauridsen, 2002;Miller & Kerfoot, 1987). ...
Communities of organisms are shaped by a complex suite of positive and negative species interactions. Ecological phenomena like biological invasions typically evoke notions of negative effects on native communities. Yet, negative effects within specific food-web components can also have positive feedbacks that manifest elsewhere within the food web. We designed an experiment to evaluate the direct and indirect effects of invasive bighead carp (Hypophthalmichthys nobilis: Cyprinidae) on planktonic and benthic invertebrates and the growth and survival of juvenile bluegill sunfish (Lepomis macrochirus: Centrarchidae). Our experiment indicated that the presence of bighead carp indirectly facilitated bluegill growth and survival. The underlying processes driving predator-predator facilitation stemmed from a combination of indirect interactions occurring through invertebrates in planktonic and vegetated habitats. Individual bluegill consumed more cladocerans and predatory macroinvertebrates in the presence of bighead carp. The presence of bighead carp appears to have indirectly influenced interactions among cladocerans, invertebrate predators, and bluegill. Understanding the cumulative direct and indirect effects of bigheaded carp on aquatic ecosystems requires the documentation of both negative and positive effects. Although one taxon benefitted from the presence of an invader, our findings demonstrate that this response occurred because bigheaded carp caused imbalances within the food web. We urge that future studies consider a priori how positive and negative interspecific interactions shape the structure of food webs.
... As a sustainable alternative, increased attention is being paid worldwide to biological means, which includes the utilization of natural predators, pathogens and parasites [4,5]. Like many predators in aquatic environments, copepods (a type of zooplankton) are known to feed voraciously on the first instar mosquito larvae resulting in strongly influencing the structural and functional organization of mosquito communities [6,7]. The copepods especially the larger cyclopoid species like Mesocyclops, Macrocyclops and Cyclops have been known to have the ability to utilize mosquito larvae as food [8]. ...
Copepods are tiny crustaceans (zooplankton) inhabiting the water bodies having rich mosquito breeding grounds and are known to act as voracious predators of first instar mosquito larvae. During the present study a survey at three districts of Punjab state (India) was carried out from various standing water bodies (n=45) to explore the occurrence of copepods coexisting with mosquito larvae. Results obtained showed the existence of copepods along with mosquito larvae in fish ponds, paddy fields and also in other small temporary water bodies. Copepod count was found to be highest in fish ponds (803.99±47.28/litre), however no copepods were observed in the water samples of village ponds. Three orders of copepods i.e. calanoida, cyclopoida and harpacticoida were observed with predominance of cyclopoids (56%). Mosquito larval population/litre was found to range from 18.84±5.66 to 182.73±21.63 from various water bodies.
... Although community ecologists have begun to study such indirect effects (e.g. Kerfoot and Sih 1987;Carpenter and Kitchell 1993), evolutionary biologists interested in life histories apparently have not done so. We show that most of the predicted direct responses to predation considered here can be reversed by strong indirect effects on food supply. ...
The effects of nonselective predation on the optimal age and size of maturity of their prey are investigated using mathematical models of a simple life history with juvenile and adult stages. Fitness is measured by the product of survival to the adult stage and expected adult reproduction, which is usually an increasing function of size at maturity. Size is determined by both age at maturity and the value of costly traits that increase mean growth rate (growth effort). The analysis includes cases with fixed size but flexible time to maturity, fixed time but flexible size, and adaptively flexible values of both variables. In these analyses, growth effort is flexible. For comparison with previous theory, models with a fixed growth effort are analyzed. In each case, there may be indirect effects of predation on the prey's food supply. The effect of increased predation depends on (1) which variables are flexible; (2) whether increased growth effort requires increased exposure to predators; and (3) how increased predator density affects the abundance of food for juvenile prey. If there is no indirect effect of predators on prey food supply, size at maturity will generally decrease in response to increased predation. However, the indirect effect from increased food has the opposite effect, and the net result of predation is often increased size. Age at maturity may either increase or decrease, depending on functional forms and parameter values; this is true regardless of the presence of indirect effects. The results are compared with those of previous theoretical analyses. Observed shifts in life history in response to predation are reviewed, and the role of size-selective predation is reassessed.
... Although it is tempting to conclude that the gradient of mean phenotypes with population homozygosity is simply a passive and maladaptive response to occasional population bottlenecks, it is also worth considering the possibility that the level of homozygosity observed within populations is more intrinsically associated with natural selection. Zooplankton communities are strongly influenced by size-selective predators (Kerfoot 1980;Kerfoot and Sih 1987), and there is no question that variation in predation can cause radical changes in species composition. Predation on temporary pond Daphnia by salamander (Ambystoma) and dip-0.1 Clarkia. ...
In an effort to elucidate the evolutionary mechanisms that determine the genetic architecture of a species, we have analyzed 17 populations of the microcrustacean Daphnia pulex for levels of genetic variation at the level of life-history characters and molecular markers in the nuclear and mitochondrial genomes. This species is highly subdivided, with approximately 30% of the variation for nuclear molecular markers and 50% of the variation for mitochondrial markers being distributed among populations. The average level of genetic subdivision for quantitative traits is essentially the same as that for nuclear markers, which superficially suggests that the life-history characters are diverging at the neutral rate. However, the existence of a strong correlation between the levels of population subdivision and broadsense heritabilities of individual traits argues against this interpretation, suggesting instead that the among-population divergence of some quantitative traits (most notably body size) is being driven by local adaptation to different environments. The fact that the mean phenotypes of the individual populations are also strongly correlated with local levels of homozygosity indicates that variation in local inbreeding plays a role in population differentiation. Rather than being a passive consequence of local founder effects, levels of homozygosity may be selected for directly for their effects on the phenotype (adaptive inbreeding depression). There is no relationship between the levels of variation within populations for molecular markers and quantitative characters, and this is explained by the fact that the average standing genetic variation for life-history characters in this species is equivalent to only 33 generations of variation generated by mutation.
... Predicting how one predator might facilitate another can be difficult, especially when resources are shared. Yet, predators directly, indirectly, positively, or negatively alter prey densities, behaviours, or distributions in complex ways (Kerfoot & Sih, 1987;Werner & Peacor, 2003 Fishes that shift foraging to alternate food resources to lessen the effects of interspecific competition may also alter their local environment by recycling nutrients, which feedback to alter the food web (e.g. ...
Ecological theory has long recognised the importance of positive and negative species interactions as drivers of food web structure, yet many studies have only focused on competition. Because competitive and facilitative mechanisms operate simultaneously, but through different food web pathways, the balance of their combined effects can produce complex and variable responses.
We used a response‐surface experimental design to assess the roles of negative (e.g. intra‐, interspecific competition) and positive (e.g. facilitation) interactions between native and invasive juvenile fishes. We tested whether these interactions alter the densities of planktonic and benthic invertebrates to evaluate the magnitude and mechanism(s) influencing the acceptance or resistance of biological invaders. Interactions between bighead carp ( Hypophthalmichthys nobilis ) and bluegill ( Lepomis macrochirus ) or common carp ( Cyprinus carpio ) were evaluated in mesocosms.
Intraspecific interactions were 1.5–2.4 times stronger than interspecific interactions between carp species. The only instance of interspecific competition resulted in bighead carp reducing the daily growth of bluegill, whereas the reciprocal interaction resulted in facilitation. Facilitation occurred when bluegill increased the daily growth of low density bighead carp treatments, despite increased numbers of fishes. Bighead carp also increased densities of benthic Chironomidae larvae, which were subsequently consumed by bluegill, but did not result in enhanced bluegill growth. These suites of interactions were not observed between common and bighead carp.
Our response‐surface design proved useful for comparing the relative magnitude of intra‐ vs. interspecific competition, identifying facilitation among species, and tracing attendant effects on invertebrate communities. By accounting for the directionality of interactions within our experimental framework and tracking responses of prey at lower trophic levels, we provide a clearer understanding of how competitive effects and stressed consumers alter prey communities and influence facilitation.
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... A prominent hypothesis is that prey should respond more strongly to predators that pose the greatest risk (Relyea 2001b). There is substantial support for this hypothesis from experimental studies, particularly with invertebrates (Kerfoot andSih 1987, Peckarsky 1996) and fish (Werner et al. 1983), but very little is known about patterns of variation in prey response to natural variation in real predation risk in the wild, particularly among the large carnivores and ungulate prey considered in this study. Thaker et al. (2011) used spatial data from a fenced reserve to infer that ungulates avoided vegetation types that were heavily used by predators, but that "the strength of avoidance for the space use of predators generally did not correspond to the relative predation threat from those predators." ...
Most species adjust their behavior to reduce the likelihood of predation. Many experiments have shown that antipredator responses carry energetic costs that can affect growth, survival and reproduction, so that the total cost of predation depends on a trade-off between direct predation and risk effects. Despite these patterns, few field studies have examined the relationship between direct predation and the strength of antipredator responses, particularly for complete guilds of predators and prey. We used scan sampling in 344 observation periods over a four-year field study to examine behavioral responses to the immediate presence of predators for a complete antelope guild (dominated by wildebeest, zebra and oribi) in Liuwa Plains National Park, testing for differences in response to all large carnivores in the ecosystem (lions, spotted hyenas, cheetahs and African wild dogs). We quantified the proportion that each prey species contributed to the kills made by each predator (516 total kills), used distance sampling on systematic line transects to determine the abundance of each prey species, and combined these data to quantify the per-capita risk of direct predation for each predator-prey pair. On average, antelopes increased their vigilance by a factor of 2.4 when predators were present. Vigilance varied strongly among prey species, but weakly in response to different predators. Increased vigilance was correlated with reduced foraging in a similar manner for all prey species. The strength of antipredator response was not detectably related to patterns of direct predation (N = 15 predator-prey combinations with sufficient data). This lack of correlation has implications for our understanding of the role of risk effects as part of the limiting effect of predators on prey. This article is protected by copyright. All rights reserved.
Even though the seasonal pattern of phytoplankton biomass distribution in the seas around India is reasonably well understood, there is relatively little information on phytoplankton size classes. The current study shows how phytoplankton of different size classes respond to nutrient enrichment caused by vertical convective mixing during the Northeast Monsoon [(NEM) November-February] and coastal upwelling during the Southwest Monsoon [(SWM) June-September] in the Eastern Arabian Sea (EAS). In the Northeastern Arabian Sea (NEAS), phytoplankton biomass [Chlorophyll-a (Chl-a)] and primary production (PP) were moderate and comparable during both the NEM (Chl-a av. 21 mg m⁻² and PP av. 601 mg C m⁻² d⁻¹) and the SWM (Chl-a av. 27 mg m⁻² and PP av. 516 mg C m⁻² d⁻¹). The Southeastern Arabian Sea (SEAS) was oligotrophic (Chl-a av. 12 mg m⁻² and PP av. 197 mg C m⁻² d⁻¹) during the NEM due to strong surface stratification, but due to coastal upwelling, it turned into a very productive system along the shelf waters during the SWM (Chl-a av. 45 mg m⁻² and PP av. 1201 mg C m⁻² d⁻¹). Interestingly, the subsurface Chl-a maximum (SCM) was almost absent in the NEAS during both seasons. Similarly, SCM was absent in the entire coastal upwelling zone of the EAS during the SWM. In these areas and situations, Chl-a was found to accumulate in the nutrient-rich surface layers of the shallow euphotic zones. The nutrient enrichment of the coastal upwelling along the shelf waters in the EAS favoured the growth of larger micro-and meso-phytoplankton during the SWM [av. 43.8 mg m⁻² (av. 65.9% total Chl-a)], whereas the entire NEAS favoured the growth of nano-phytoplankton during the NEM [av. 13.9 mg m⁻² (av. 64.8% total Chl-a)]. Differences in the physical processes enabling the entrainment of nutrients (Nitrate (NO3), Phosphate (PO4) and silicate (SiO4)] into the euphotic layer could explain the observed differences in the phytoplankton size fractions. The convective mixing in the NEAS during the NEM erodes the bottom of the mixed layer (50-120 m), resulting in only moderate enrichment of NO3 (av. 0.62 ± 0.45 µM) and SiO4 (av. 3.01 ± 0.83 µM), and low level of PO4 (av. 0.49 ± 0.13 µM) in the mixed layer (av. 60 m). This caused N -limitation in the NEAS, which favoured the dominance of nano-phytoplankton. Alternatively, coastal upwelling during the SWM drives deeper subsurface waters (75-150 m) into the shallow surface mixed layer (av. 30 m) in shelf water, causing significant enrichment of NO3 (av. 11.02 ± 3.55 µM), SiO4 (av. 18.34 ± 11.37 µM) and PO4 (av. 1.15 ± 0.21 µM). The enhanced nutrients in the coastal upwelling zones favoured the dominance of larger micro and meso-phytoplankton. However, during the SWM, the oceanic waters of the entire EAS showed low nutrient concentration compared to the shelf waters, which favoured the dominance of nanophytoplankton. In conclusion, our work reveals the large contribution of nano-phytoplankton in Chl-a biomass across the entire EAS, underlining their ecological relevance in both N-limited and N-enriched environments.
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• One of the major research goals in ecology is to understand predator–prey interactions. However, our understanding of how prey express phenotypic plasticity in response to co-occurring multiple predators is limited in many systems.
• Here, we use the rotifer Brachionus calyciflorus as model organism to test how prey responds to co-occurring predators through a series of related experiments. Firstly, we examined the effects of the density of a fish predator Carassius auratus on morphological traits in B. calyciflorus. Secondly, we examined the effects of larval C. auratus and Asplanchna brightwellii (a rotifer predator) on morphological defensive traits (body length, body width, anterior spine length, and posterolateral spine length) of B. calyciflorus.
• We show that B. calyciflorus develops smaller body size and shorter spine length when exposed to media conditioned using larval fish, and that high larval fish densities induce more pronounced responses than low densities. We also show that B. calyciflorus is able to discriminate between the two predators by producing opposing morphological adaptations (i.e., larger body size and longer posterolateral spines against A. brightwellii, but smaller body size and shorter spine length when exposed to the visual predator [larval fish]). However, B. calyciflorus develops intermediate, trade-off responses in all morphological traits when exposed to conflicting threats from a combination of predators with different size and feeding strategies.
• These results show how prey are not necessarily passive victims, but rather, use countermeasures against predation – they actively develop responses to counteract their vulnerability to different predators by rapidly adjusting their morphology and life-history traits to the existing predator regimes.
• Invasive species represent one of the greatest threats to freshwater biodiversity. The successful colonisation and establishment of populations of invasive predators in waterbodies may expose the pre-existing fauna to novel predation strategies to which they are not pre-adapted. Despite this, there is still a paucity of information on behavioural responses within biological invasion research.
• Here we present the results of a series of 24-hr mesocosm experiments that examined the handling times and responses of four Gastropoda species (Radix balthica, Physa fontinalis, Gyraulus albus, Potamopyrgus antipodarum) exposed to physical and chemical cues associated with the invasive crayfish, Pacifastacus leniusculus. We specifically considered four physicochemical treatments: (1) control (no cue); (2) conspecific chemical; (3) crayfish chemical; and (4) physical presence (but confined). In addition, we considered the effect of previous predator experience of the gastropod (predator naïve or aware) and additonally assessed survivourship in encounter trials.
• Handling time was found to vary significantly between gastropod species with survivorship from predation mirroring handling times observed. P. fontinalis required the greatest handling time (average of 58 s) and had the highest survivorship rate. In marked contrast, P. antipodarum were rapidly consumed, with an average handling time of 6 s and no individuals surviving after 4-hr in the encounter trials. Handling time varied by gastropod size but also shell morphology.
• The response to the physical and chemical cues varied between gastropod species. R. balthica and P. fontinalis demonstrated vertical avoidance behaviour most readily whilst P. albus and P. antipodarum displayed active migration only to the physical presence cue. In most instances, the response was immediate with vertical migration (above the reach of the crayfish at 15 cm on the mesocosm wall) evident within an hour.
• Predation regime was found to exert a significant effect on the avoidance response of the gastropods. This was particularly notable in relation to the crayfish chemical cue and to a lesser extent the injured conspecific chemical cue. Predator-naïve populations reacted with strong vertical avoidance behaviour in response to the crayfish chemical cue, whilst, in the case of P. fontinalis, predator aware individuals reacted most strongly to the conspecific chemical cue.
• Our results highlight the multifaceted challenge of understanding predator–prey relationships, particularly in the face of novel invasive species, and provide much-needed evidence to begin to tackle this complex process. Gaining a better understanding of such interactions is vital in order to underpin management strategies and to enable evolutionary trajectories in invaded ecosystems to be assessed. Previous predator experience in combination with species identity are important attributes in determining predation risk when gastropod populations are exposed to novel predators and their associated predation cues.
Fish and other fishery resources are representing most important faunal components in the riverine ecosystem by virtue of their vivid presence and functional roles towards stability of the lotic ecosystem. They are in utmost need of protection and conservation for themselves and their habitats because of the dependence of human beings on this gift of the nature as important sources of food (chief sources of proteins), from aquatic ecosystems.
In the process of avoiding predation, prey are faced with potentially fitness‐compromising trade‐offs that have implications for their survival and reproduction. The nature and strength of these non‐consumptive effects at the population level can be equivalent, or even greater, than consumptive effects.
Many prey species have evolved defence mechanisms that are induced by predation risk. These inducible defences can be morphological or behavioural in nature. Extensive research has detected these defences in predator–prey communities across freshwater, marine and terrestrial ecosystems. Among this vast research however, an influential portion of these systems has not been widely considered.
Humans inhabit a level in trophic systems above apex predators. In that position, humans have been referred to as a hyperkeystone or super predator species as they have shown a capacity to consume animals at rates many times higher than any other non‐human species. However, the extent to which humans induce adaptive defences in animals is not as clear. Systems involving large mammals may be particularly well‐suited for the study of human‐induced defences given that these species have been disproportionately exploited (for food and competition) over evolutionary time by humans.
To begin this process we first had to examine the context in which large mammals could adaptively evolve inducible defences in relation to human lethality. With the plausibility of these conditions satisfied, we then conducted an extensive review to document the inducible defences that have been detected in large mammals. All of the 187 studies reviewed documented the behavioural plasticity of large mammals to human lethality. No morphological adaptive defences were detected.
However, the extent to which the observed behavioural plasticity of large mammals is representative of adaptive inducible defences remains unclear because the fitness trade‐offs (i.e. costs), an integral condition for inducible defences to evolve, were implied rather than quantified among close to 92% of this research. We make recommendations for renewed ingenuity in the development of field experiments that can quantify these costs and discuss the implications of human lethality on the ecology, conservation and management of large mammals.
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Enemy-risk effects, often referred to as non-consumptive effects (NCEs), are an important feature of predator-prey ecology, but their significance has had little impact on the conceptual underpinning or practice of biological control. We provide an overview of enemy-risk effects in predator-prey interactions, discuss ways in which risk effects may impact biocontrol programs and suggest avenues for further integration of natural enemy ecology and integrated pest management. Enemy-risk effects can have important influences on different stages of biological control programs, including natural enemy selection, efficacy testing and quantification of non-target impacts. Enemy-risk effects can also shape the interactions of biological control with other pest management practices. Biocontrol systems also provide community ecologists with some of the richest examples of behaviourally mediated trophic cascades and demonstrations of how enemy-risk effects play out among species with no shared evolutionary history, important topics for invasion biology and conservation. We conclude that the longstanding use of ecological theory by biocontrol practitioners should be expanded to incorporate enemy-risk effects, and that community ecologists will find many opportunities to study enemy-risk effects in biocontrol settings.
Predator‐prey size (PPS) relationships are determined by predator behaviour, with the likelihood of prey being eaten dependent on their size relative to that of the consumer. Published PPS relationships for 30 pelagic or benthic marine fish species were analysed using quantile regression to determine how median, lower, and upper prey sizes varied with predator size and habitat. Habitat effects on predator foraging activity/mode, morphology, growth, and natural mortality are quantified and the effects on PPS relationships explored. Pelagic species are more active, more likely to move by caudal fin propulsion, and grow more rapidly but have higher mortality rates than benthic species, where the need for greater manoeuvrability when foraging in more physically complex habitats favours ambush predators using pectoral fin propulsion. Prey size increased with predator size in most species but pelagic species ate relatively smaller prey than benthic predators. As pelagic predators grew lower prey size limits changed little and prey size range increased but median relative prey size declined, whereas the lower limit increased and median relative prey size was constant or increased in benthic species.
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Hydrodynamics and pollution affect estuarine populations, but their ecological effects have rarely been studied in combination. We conducted two laboratory experiments to quantify whether predator–prey interactions between California killifish, Fundulus parvipinnis, and the polychaete Polydora cornuta vary with flow speed and chlorpyrifos exposure. In one experiment, only F. parvipinnis was exposed to chlorpyrifos; in the other, only P. cornuta was exposed. The flume included a 300-cm² area of sediment with 24 P. cornuta in a central patch (98 cm²). We videotaped groups of three killifish for 50 min at one of four flow speeds (6, 9, 12, or 15 cm/s) and recorded the proportion of bites directed at the prey patch. Unexposed killifish directed 70% of their bites at the prey patch at 6 cm/s, and prey-patch selection decreased as flow increased. Killifish exposed to chlorpyrifos directed 41% of their bites at the prey patch at 6 cm/s with reduced prey-patch selection relative to unexposed fish at 9 and 12 cm/s. At 15 cm/s, both exposed and unexposed fish displayed non-selective biting. Worms were videotaped to quantify their deposit- and suspension-feeding activities. Exposing worms to chlorpyrifos reduced total feeding activity by ~30%. Suspension feeding was more common at faster flow speeds, but the time worms spent suspension feeding relative to deposit feeding was unaffected by chlorpyrifos. No behavioral changes were noted in either species when the other was exposed to chlorpyrifos. This study highlights how hydrodynamic conditions can alter the relative importance of a toxicant’s effects on predator–prey interactions.
Phenotypic plasticity is a common defensive strategy in species experiencing variable predation risk, such as habitat generalists. Larvae of generalist dragonflies can elongate their abdominal spines in environments with fish, but long spines render larvae susceptible to invertebrate predators. Long-spined specialists adapted to fish-heavy habitats are not expected to have phenotypic plasticity in this defence trait, but no empirical studies have been undertaken. Moreover, in comparison to prey responding to multiple predators that induce similar phenotypes, relatively little is known regarding how species react to combinations of predators that favour opposing traits. We examined plasticity of larval dragonfly Sympetrum depressiusculum, a long-spined habitat specialist. In a rearing experiment, larvae were exposed to four environments: (i) no predator control, (ii) fish cues (Carassius auratus), (iii) invertebrate cues (Anax imperator), as well as (iv) a combination of (ii) and (iii). Compared with the control, fish but not invertebrate cues resulted in longer spines for two (one lateral, one dorsal) of the six spines measured. Interestingly, the combined-cue treatment led to the elongation of all four dorsal spines compared with the fish treatment alone, whereas lateral spines showed no response. Our experiment provided evidence of morphological plasticity in a long-spined specialist dragonfly. We showed that nearly all spines can elongate, but also react differently under specific predator settings. Therefore, while spine plasticity evolved in direct response to a single predator type (fish), plasticity was maintained against invertebrate predators as long as fish were also present. Selective spine induction under the combined condition suggests that S. depressiusculum can successfully survive in environments with both predators. Therefore, phenotypic plasticity may be an effective strategy for habitat generalists and specialists. Although more studies are necessary to fully understand how selection shapes the evolution of phenotypic plasticity, we demonstrated that in dragonflies, presence or absence of a specific predator is not the only factor that determines plastic defence responses.
Mandarin fish Siniperca chuatsi, a valuable piscivorous fish, have been stocked into many lakes in China since the 1990s. This study did the first attempt to evaluate the ecological effects of hatchery-reared mandarin fish stocking in the Yangtze River basin lakes. Our study demonstrated a significant change in fish community composition after mandarin fish stocking, but no fish extinction was observed. No significant difference was observed in the total density of 13 forage fish before and after mandarin fish stocking, but the total biomass showed a significant decline after mandarin fish stocking. Significant differences in length-frequency distributions were observed for Carassius auratus, Pseudorasbora parva and Toxabramis swinhonis captured before and after stocking mandarin fish. No significant change in habitat distribution was detected before and after mandarin fish stocking. A marked decline in total nitrogen and a slight decline in total phosphorus were observed while a slight increasing trend for Secchi depth was found after stocking. Our findings suggested that mandarin fish stocking can increase predation pressure on forage fish and subsequently optimize the food web structure. Also, mandarin fish stocking has the potential to improve water quality and may be a feasible strategy to alleviate eutrophication of shallow Yangtze lakes.
Improved vision due to the cranial endothermy known in large-bodied marine fishes suggests that increased water temperature alone might also increase the speed with which visual information can be processed and therefore improve the vision of small planktivorous fish without invoking endothermic heating. We check this for two freshwater species by testing whether a temperature increase results in an increase in the reaction distance (RD), the distance from which a foraging fish can spot its tiny zooplankton prey. We demonstrate that at a given light intensity, with a temperature increase of 10°C, both the reaction field volume and prey encounter rate of planktivorous fish are doubled due to a 21–23% increase in RD. This was found for each of the two small-bodied freshwater planktivorous fishes: rudd from the temperate zone (foraging at 16°C and 26°C), and Malabar danio from the tropics (foraging at 21°C and 31°C), and may be expected to be important for other fishes as well. An increase in RD at a higher temperature could translate into a higher “apparent prey density” or number of prey within the reaction field volume of a foraging fish (a vertically flattened hemisphere or cone with a horizontal radius equal to the RD). For fish in the wild, this information may compel them to continue foraging despite a low actual density of prey in the habitat. This is particularly important while feeding under the risk of predation, when attention is partially allocated to risk assessment.
Why study food webs in lakes? From a basic research perspective, ecological studies of lake food webs provide distinct advantages over studies in many terrestrial systems (Lampert 1987). Lake food webs are composed of organisms with relatively fast population turnover rates which interact in a relatively closed system. These features allow us to readily observe the often rapid dynamics of these systems or to experimentally manipulate these food webs and quickly assess the system response. Enclosures, ponds, and whole-lake manipulations are extremely useful experimental tools that have allowed aquatic ecologists to test hypotheses on food web structure and function that would have been difficult or impossible to address in many terrestrial systems.
Few predation models that simulate effects on prey survival and size structure also predict the corresponding effects on predator growth and size structure. To make this link, we parameterized a bioenergetics model for southern flounder Paralichthys lethostigma by conducting a series of respiration and feeding experiments as well as obtaining values from the literature. We then linked the bioenergetics model to an existing size-dependent foraging model for southern flounder feeding on spot Leiostomus xanthurus and tested it using data from a pond experiment. Integrating these two models allowed us to investigate the effects of size-dependent interactions on predator growth by making predator growth a function of size-dependent foraging success. The linked model predicts spot effects as well as the original foraging model does, but the accuracy of flounder growth predictions were size-dependent. Predictions of prey survival and size structure were robust and were not greatly affected by slight changes in predator foraging rates, but predictions of predator growth rate were very sensitive to slight changes in predicted foraging rates. This asymmetry in the linked model's predictive ability is derived from the nonlinearity of the prey length-mass relationship and the different currencies used by the foraging component (number of prey eaten) and the bioenergetics component (mass of prey eaten) of the linked model. Because bioenergetics model predictions of growth are inherently sensitive to estimates of food consumption, this asymmetry in ability to predict effects on prey numbers and predator growth will likely be a common feature of similarly linked models.
The frequent use of neutral markers to quantify genetic variation in natural populations emphasizes the role of stochastic events in explaining genetic differentiation between populations. Complementary studies on ecologically relevant traits are needed to assess the role of natural selection acting on adaptive variation in the development of local genetic differentiation. To test the hypothesis of local adaptation in the cyclical parthenogenetic species Daphnia magna, the phototactic behavior in the absence and presence of fish kairomone was assayed for 30 clones derived from resting eggs isolated from three habitats characterized by a different predation pressure by fish. Clones derived from populations in which fish are present were, on average, more negatively phototactic in and more responsive to the presence of fish kairomone than clones derived from a fishless habitat. In addition, the results show a high genetic diversity for the traits studied in all three gene pools investigated, indicating a high potential for microevolutionary changes in behavior of these Daphnia populations in the face of changes in predation pressure. The results of the present study indicate that working with large samples at the expense of having less precise estimates of genotypic values for specific genotypes may result in a loss of information with regard to the evolutionary potential of local populations.
Professor Gerald Esch‘s primary bases of operations for research and those of his students were Gull Lake in Michigan and the Par Pond reservoir at the Savannah River Plant (SRP) in South Carolina. Duke Energy's power plant at Belews Lake used to deposit a considerable amount of fly that was converted into a slurry and transported to a settling basin. The story of B. acheilognathi in Belews Lake probably began in 1977 when fathead minnows were discovered during cove rotenone surveys routinely employed by Duke Energy to census the fish community. The chapter also explains how a tapeworm was found in the intestine of a mosquitofish and how cestode is highly invasive and had been found throughout Europe and North America down into Mexico. Another important observation was that naturally infected mosquitofish died much sooner than uninfected G. affinis under similar laboratory conditions.
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