James F Gilliam

North Carolina State University | NCSU · Department of Biological Sciences

Detrital‐based trophic cascades are often considered weak or absent in tropical stream ecosystems because of the prevalence of omnivorous macroconsumers and the dearth of leaf‐shredding insects. In this study, we isolate top‐down effects of three macroconsumer species on detrital processing in headwater streams draining Trinidad's northern mountain...

Migratory fishes can be threatened by conditions encountered along dispersal pathways that impede access to feeding or breeding grounds. In this study, we tested the hypothesis that amphidromous fishes are equally or more sensitive to conditions along dispersal pathways than conditions in primary residential habitats. We did so by conducting distri...

Urbanisation is widely associated with a suite of physical, chemical and biological degradation of stream ecosystems, known as “urban stream syndrome.” It is unclear whether urban stream syndrome is applicable to oceanic islands, where marine dispersal of larvae enables diadromous species to continuously recolonise even highly degraded urban stream...

While previous studies have shown that evolutionary divergence alters ecological processes in small-scale experiments, a major challenge is to assess whether such evolutionary effects are important in natural ecosystems at larger spatial scales. At the landscape scale, across eight streams in the Caroni drainage, we found that the presence of local...

Species introductions are a widely recognized threat to global freshwater biodiversity. The proliferation of non-native species can result in the loss of native species through direct and indirect interactions with predators, competitors, pathogens and parasites. Thus identifying invasion hotspots and understanding the capacity of vulnerable ecosys...

Points of origin and pathways of spread are often poorly understood for introduced parasites that drive disease emergence in imperiled native species. Co-introduction of parasites with non-native hosts is of particular concern in remote areas like the Hawaiian Islands, where the introduced nematode Camallanus cotti has become the most prevalent par...

High-resolution analysis of growth increments, trace element chemistry and oxygen isotope ratios (δ18O) in otoliths were combined to assess larval and post-larval habitat use and growth of Awaous stamineus, an amphidromous goby native to Hawai‘i. Otolith increment widths indicate that all individuals experience a brief period of rapid growth during...

SUMMARY The presence of introduced hosts can increase or decrease infections of co-introduced parasites in native species of conservation concern. In this study, we compared parasite abundance, intensity, and prevalence between native Awaous stamineus and introduced poeciliid fishes by a co-introduced nematode parasite ( Camallanus cotti ) in 42 wa...

Visual surveys are conducted to rapidly estimate population densities of stream fishes, often without calibration against more established or more widely used methods to determine precision and accuracy or to correct for potential biases. We compared population density estimates from a visual survey (VS) point quadrat method widely used in Hawaii w...

It is widely accepted that insular terrestrial biodiversity progresses with island age because colonization and diversification proceed over time. Here we assess whether this principle extends to oceanic island streams. We examined range-wide mtDNA sequence variation in four stream-dwelling species across the Hawaiian archipelago to characterize th...

Dietary patterns of animals have a long-recognized importance in ecology and evolution, with numerous and diverse applications. While many methods of diet assessment exist, the most common method of direct diet examination for most small vertebrates is stomach-content analysis, using labor-intensive surgical removal of the gut following death. Meth...

SUMMARY 1. Co-introductions of non-native parasites with non-native hosts can be a major driver of disease emergence in native species, but the conditions that promote the establishment and spread of nonnative parasites remain poorly understood. Here, we characterise the infection of a native host species by a non-native parasite relative to the di...

Successful dispersal can enhance both individual fitness and population persistence, but the process of dispersal is often inherently risky. The interplay between the costs and benefits of dispersal are poorly documented for species with complex life histories due to the difficulty of tracking dispersing individuals. Here we investigate variability...

The influence of habitat fragmentation on population dynamics within watersheds is not well understood, particularly for species known to disperse great distances. Effective conservation management, however, relies in part on an understanding of the role connectivity plays in maintaining viable populations over time and space. This study examined w...

Background/Question/Methods Despite empirical evidence that evolution can influence populations, communities and ecosystems, we do not know if the ecological effects of evolution are frequent and strong enough to regulate communities and ecosystems in nature. We examine how trait variation (diet selectivity and life history) in locally adapted Tr...

Based on historical and museum records and recent extensive collecting we compiled a checklist of 77 fish species reported from the streams of Trinidad and Tobago. A key with photographs is provided to aid in identifications, as well as brief notes on habitat, diet, reproduction, maximum size, local common names and distribution.

Based on historical and museum records and recent extensive collecting we compiled a checklist of 77 fish species report-ed from the streams of Trinidad and Tobago. A key with photographs is provided to aid in identifications, as well as brief notes on habitat, diet, reproduction, maximum size, local common names and distribution. Key words: biod...

Background/Question/Methods Ecological processes have long been known to affect evolution, yet only recently has there been experimental evidence of evolution affecting ecological processes. We examine how trait variation (diet selectivity) in Trinidadian guppies affects stream ecosystems at local and landscape scales to address the question: Are...

Non-native species and habitat degradation are two major catalysts of environmental change and often occur simultaneously. In freshwater systems, degradation of adjacent terrestrial vegetation may facilitate introduced species by altering resource availability. Here we examine how the presence of intact riparian cover influences the impact of an in...

Calculation of NH4-N uptake length, uptake velocity, and areal uptake rate in Ramdeen Stream. (DOCX)

Nutrient limitation in Ramdeen Stream. Mean chlorophyll a on nutrient diffusing substrates after a two-week incubation in RAM. Asterisk indicates significantly greater chlorophyll a relative to controls using a randomized block ANOVA (p<0.001). Results revealed that algal accrual was co-limited by N and P availability, as substrates containing both...

Stoichiometry of T. granifera body tissue. Mean (±1SE) body tissue C:N and C:P of T. granifera (shell removed) in open and closed canopy habitat. RAM = Ramdeen Stream, ARI = Aripo River. (DOCX)

Short-term NH4 addition in Ramdeen stream in 2008 and 2010. Tracer NH4-N and conductivity are concentrations at plateau corrected for background concentrations. Distance from injection site indicates location downstream from site where solutes were added using a peristaltic pump. (TIF)

Nutrient limitation in Ramdeen Stream as measured using nutrient diffusing substrates. (DOCX)

Measurement of C, N, and P stoichiometry of T. granifera body tissue. (DOCX)

Questions remain about the taxonomy and distribution of geographically widespread species in the circumtropical gobiid genus Awaous. Previous work that placed two species in synonymy on the basis of morphological characteristics effectively redefined the range of Awaous guamensis to include distant locations from Hawai’i and Guam to the islands of...

The elemental composition of animals, or their organismal stoichiometry, is thought to constrain their contribution to nutrient recycling, their interactions with other animals, and their demographic rates. Factors that affect organismal stoichiometry are generally poorly understood, but likely reflect elemental investments in morphological feature...

Sampling of environmental variables and basal resource quality. (DOC)

Average stoichiometry of epilithon and benthic organic matter (BOM) collected from each site. (DOC)

Least squares (LS) means generated by the stage of maturity×community interaction. (DOCX)

Amphidromous fishes are important members of oceanic island freshwater communities. Although often depauperate, amphidromous fish assemblages on islands are largely composed of endemic species. Little is known about the effects of anthropogenic stressors on amphi - dromous fishes, and the consequences of climate-driven changes in water quality and...

The extreme isolation of the Hawaiian archipelago has resulted in low diversity, high endemism and strong representation by amphidromous taxa among the freshwater fauna. Due to the obligatory migration of the Islands’ freshwater fish species, modeling impacts of land use, in-stream habitat and exotic species presents additional and unique challenge...

Background/Question/Methods The extreme isolation of the Hawaiian archipelago has resulted in low diversity, high endemism and strong representation by amphidromous taxa among the freshwater fauna. Due to the obligatory migration of the Islands’ freshwater fish species, modeling impacts of land use, in-stream habitat and exotic species presents a...

Background/Question/Methods Species that compete strongly for resources coexist in nature more often than classic Lotka-Volterra models of competition would predict. Intraguild predation can facilitate the coexistence of competing species, especially when the weaker competitor is the more effective predator. As part of a larger study of the feedb...

Diel migrations of the golden shiner (Notemigonus crysoleucas) from the littoral to limnetic zone of a small Michigan lake were documented through visual observations and gill netting. During the day golden shiners schooled in the littoral zone. Just after sunset schools broke up and the golden shiner migrated to the open water regions of the lake....

Diversification of freshwater fishes on islands is considered unlikely because the traits that enable successful colonization-specifically, broad salinity tolerances and the potential for oceanic dispersal-may also constrain post-colonization genetic differentiation. Some secondary freshwater fish, however, exhibit pronounced genetic differentiatio...

Forager (predator) abundance may mediate feeding rates in wading birds. Yet, when modeled, feeding rates are typically derived from the purely prey-dependent Holling Type II (HoII) functional response model. Estimates of feeding rates are necessary to evaluate wading bird foraging strategies and their role in food webs; thus, models that incorporat...

Background/Question/Methods Whole stream addition of enriched stable isotopes is a powerful method for quantifying biogeochemical cycling and trophic dynamics in lotic ecosystems. However, most isotopic tracer studies have occurred in temperate North American streams, and the approach has been largely neglected in tropical running water systems. U...

Background/Question/Methods The distributions of most species of fish in dendritic drainages show distributions analogous to a pruned tree, with the trunk and perhaps some branches (tributaries) remaining. However, some species show the near complement of that pattern, with presence or highest densities at the tips of the branches, as if the trunk...

Immigration, emigration, migration, and redistribution describe processes that involve movement of individuals. These movements are an essential part of contemporary ecological models, and understanding how movement is affected by biotic and abiotic factors is important for effectively modeling ecological processes that depend on movement. We asked...

The addition of nocturnal, Hoplias malabaricus, and diurnal, Crenicichla alta, predatory fishes downstream of barrier waterfalls increases predation threat for a killifish, Rivulus hartii, in Trinidadian streams. We hypothesized that the diel patterning of predation risk would affect prey movement rates, and tested this hypothesis by comparing move...

Both federal and state governments have regulations requiring road crossings to facilitate Aquatic Organism Passage (AOP). Due to a current inability to prove that AOP will not be inhibited, acquiring permits for the design and construction of culverts has become difficult. Often, bridges costing up to three times as much must be built in their pla...

The nonlethal effects of predation threat can be pervasive but are also easily overlooked. We investigated effects of predation threat on feeding by guppies (Poecilia reticulata), and how threat-induced temporal shifts in feeding activity affect reproductive behavior and growth. Contrary to the view of the guppy as a ''diurnal'' species, our ob-ser...

Documents the widespread existence of ontogenetic shifts in diet and habitat and explores the consequences of such shifts for species interactions and community structure. Most examples are from the lower vertebrates and invertebrates in freshwater communities. The second part offers a conceptual framework for predicting ontogenic shifts and sugges...

We develop a general theory of organism movement in heterogeneous populations that can explain the leptokurtic movement distributions commonly measured in nature. We describe population heterogeneity in a state-structured framework, employing advection-diffusion as the fundamental movement process of individuals occupying different movement states....

Many empirical studies support the premise that animals consider both the benefits of feeding and the cost of mortality when making behavioral decisions, and many theoretical studies predict animal behavior in the presence of a feeding-mortality trade-off. However, empirical work is lacking in studies that quantitatively assess alternative models....

Many empirical studies support the premise that animals consider both the benefits of feeding and the cost of mortality when making behavioral decisions, and many theoretical studies predict animal behavior in the presence of a feeding‐mortality trade‐off. However, empirical work is lacking in studies that quantitatively assess alternative models....

A predator's per capita feeding rate on prey, or its functional response, provides a foundation for predator–prey theory. Since 1959, Holling's prey-dependent Type II functional response, a model that is a function of prey abundance only, has served as the basis for a large literature on predator–prey theory. We present statistical evidence from 19...

Leptokurtic distributions of movement distances observed in field-release studies, in which some individuals move long distances while most remain at or near their release point, are a common feature of mobile animals. However, because leptokurtosis is predicted to be transient in homogeneous populations, persistent leptokurtosis suggests a populat...

Leptokurtic distributions of movement distances observed in field‐release studies, in which some individuals move long distances while most remain at or near their release point, are a common feature of mobile animals. However, because leptokurtosis is predicted to be transient in homogeneous populations, persistent leptokurtosis suggests a populat...

Movement by stream fish is known to be strongly influenced by abiotic factors such as floods and temperature, but roles of biotic factors, such as predation threat, and interactions of abiotic and biotic factors are less clear. Predation threat is known to fragment populations of killifish, Rivulus hartii, in Trinidad rivers by rendering habitat in...

Using a mark-recapture technique in a small temperate stream, we described the movement of four fish species over a five-month period and developed a mathematical model that described the observed movement patterns. The movement distributions were generally leptokurtic, and two of the four species demonstrated some degree of upstream bias. There wa...

Stream fish often occur in tributaries at high densities, and dispersal between tributaries must occur through the intervening river, whose attributes may differ from those of the tributaries. In Trinidad, tributaries of the Guanapo River have high densities of a killifish, Rivulus hartii, but the river also contains a strong piscivore that may aff...

Studying one of two bear species not experiencing widespread population decline, provides insight into the population responses of the six bear species that are in decline and into responses of other long-lived species for which data are difficult to collect. Black bear (Ursus americanus) sanctuaries were established in North Carolina (U.S.) in 197...

Stream fish sometimes show multimodal distributions, with high densities in the tributaries of a river but rarity or absence in the river itself. To assess if predation can produce such a fragmented distributional pattern on a large geographic scale, we determined the density and habitat use of a prey fish in two tropical stream watersheds, each wi...

Ideal Free theory has furthered our understanding of the processes determining the distribution of mobile foragers in a spatially heterogeneous (patchy) habitat. The Input Matching rule derived from Ideal Free theory has been used to predict forager distributions, but does not account for unshared environmentally induced costs that individuals may...

Examined the fish community of a tropical watershed in the Northern Range Mountains of Trinidad. One member of the fauna, a killifish, Rivulus hartii, was widely distributed in the drainage, occurring alone in each headwater but also encountering other fish species below barrier waterfalls. Rivulus was used to test four predictions derived from the...

We asked whether invasions by a predator in a patchy environment altered only the death rate of the prey, or whether there were also nonlethal effects, i.e., alterations in three other vital rates: net emigration, reproduction, and individual growth rates. Field studies documented the patch use of the guppy Poecilia reticulata and the killifish Riv...

In nature, foraging animals are members of food webs, in which a given forager seeks to consume other organisms, and might itself be eaten by other predators. Studies of diet choice usually focus on a forager and “lower” levels in the web, i. e. the forager and its potential prey. This focus on the forager and its prey has indeed been a very effect...

Examined whether variation in the local density of small juvenile creek chubs Semotilus atromaculatus would, in turn, produce local alterations in the stream benthic invertebrate community. Over 3 mo, the presence of fish resulted in reductions of 79-90% in total invertebrate volume relative to the zero-fish treatments. Numbers were reduced 55-61%....

Individuals of different sizes in size-structured populations often differ greatly in the use of resources and/or space. Spectacular examples include shifts, within a lifetime, from carnivory to herbivory (e.g., some turtles; Clark and Gibbons 1969), or from herbivory to carnivory (e.g., some copepods; Neill and Peacock 1980), or from aquatic to te...

Animals commonly choose among habitats that differ both in foraging return and mortality hazard. However, no experimental study has attempted to predict the level of increase in resources, or the decrease in mortality hazard, which will induce a forager to shift from a safer to a more hazardous (but richer) foraging area. Here we present and test a...

Populations of guppies, Poecilia reticulata and Hart's rivulus, Rivulus harti, in Trinidad experience different levels of predation hazard from piscivorous fish. Those from the larger rivers (downstream sites) experience chronically high predation hazard, while those from headwater streams (upstream sites) have few predators. Guppies and Hart's riv...

Identical populations of 3 size-classes of bluegill sunfish Lepomis macrochirus were stocked on both sides of a divided pond (29m in diameter), and 8 piscivorous largemouth bass Micropterus salmoides were introduced to one side. Only the small size-class suffered significant mortality from the bass (each bass consumed on average about one small blu...

Utilizing optimal foraging theory and laboratory estimates of foraging costs, the choice of foods and use of habitats by fish in the field are predicted. Predictions are tested with bluegill sunfish Lepomis macrochirus foraging in open water, sediments, and vegetation in a pond. The optimal diet and profitability (net energy return) for each habita...

Thesis (Ph. D.)--Michigan State University. Dept. of Zoology, 1982. Includes bibliographical references (leaves 102-104). Microfilm. s

ACKNOWLEDGMENTS Many individuals aided in the completion of this project. Jim Borawa, Regional Fisheries Biologist, North Carolina Wildlife Resources Commission, initiated the supplemental

Resources fluctuate in space and time, and animals routinely experience temporally varying opportunities for resource intake, and variation in intake itself. We investigate consequences of such variation in intake on growth and growth efficiency (growth per unit intake) in juvenile hybrid striped bass. We observed, after statistically accounting fo...