Availability Of Prey Resources Research Articles

Geographical, temporal, and individual-based differences in the trophic ecology of female Cape fur seals.

Information on resource use and trophic dynamics of marine predators is important for understanding their role in ecosystem functioning and predicting population-level responses to environmental change. Where separate populations experience different local environmental conditions, geographic variability in their foraging ecology is often expected. Within populations, individuals also vary in morphology, physiology, and experience, resulting in specialization in resource use. In this context, isotopic compositions of incrementally grown tissues such as keratinous hairs offer a valuable opportunity to study long-term variation in resource and habitat use. We investigated the trophic ecology of female Cape fur seals (Arctocephalus pusillus pusillus) using carbon and nitrogen isotopic compositions of serially sampled whiskers collected at four breeding sites along the coast of South Africa. Drawing on over 900 isotopic measurements, we assessed geographic variability in isotopic niche width between colonies and the degree of individual specialization. We found slight, but clear geographic differences in isotopic ratios and isotopic niche widths, seemingly related to ecological setting, with niche widths being proportional to the area of available shelf and shelf-slope habitat surrounding the colony. We further identified periodic oscillations in isotopic ratios, which likely reflect temporal patterns in foraging distribution and prey type, linked to shifts in the availability of prey resources and their interaction with constraints on individual females throughout their breeding cycle. Finally, individual specialization indices revealed that each of the study populations contain specialist individuals that utilize only a small subset of the total population niche width. The degree of individual specialization was, however, not consistent across colonies and may reflect an interactive influence between density-dependent effects and habitat heterogeneity. Overall, this study provides important information on the trophic ecology of Cape fur seals breeding in South Africa and highlights the need to consider geographic and individual variability when assessing the foraging ecology of marine predators.

Asociación de la temperatura superficial del mar y la abundancia del Piquero Café (Sula leucogaster) según el estado de desarrollo en el Parque Nacional Natural Gorgona

La variación de las condiciones fisicoquímicas del mar puede influir en la distribución y la abundancia de las aves marinas al afectar la estructura trófica del ambiente pelágico. Por ello se pretendió evaluar la asociación entre la abundancia de tres estados de desarrollo (pollos, juveniles y adultos) del Piquero Café (Sula leucogaster etesiaca) y la variación de la temperatura superficial del mar (TSM) y su anomalía térmica (ANOM) en isla Gorgona, Pacífico colombiano. Estas tendencias fueron evaluadas por medio de correlaciones cruzadas y modelos lineales generalizados. En cada estado de desarrollo la abundancia presentó una tendencia diferente ante la variación de la TSM o ANOM. Se sugiere que dichas tendencias se deben a que el incremento de la temperatura del mar podría estar asociado con una menor abundancia y disponibilidad de recursos presa. Bajo estas condiciones, los adultos tienden a disminuir el esfuerzo invertido en el cuidado parental e, incluso, reducen el suministro de alimento a juveniles dependientes y pollos para aumentar su propia supervivencia. Es posible que estas tendencias hayan estado asociadas con un régimen reproductivo que les permita a los volantones alcanzar la independencia de los padres durante el periodo con mayor disponibilidad de alimento.

Extreme environmental conditions reduce coral reef fish biodiversity and productivity

Tropical ectotherms are hypothesized to be vulnerable to environmental changes, but cascading effects of organismal tolerances on the assembly and functioning of reef fish communities are largely unknown. Here, we examine differences in organismal traits, assemblage structure, and productivity of cryptobenthic reef fishes between the world’s hottest, most extreme coral reefs in the southern Arabian Gulf and the nearby, but more environmentally benign, Gulf of Oman. We show that assemblages in the Arabian Gulf are half as diverse and less than 25% as abundant as in the Gulf of Oman, despite comparable benthic composition and live coral cover. This pattern appears to be driven by energetic deficiencies caused by responses to environmental extremes and distinct prey resource availability rather than absolute thermal tolerances. As a consequence, production, transfer, and replenishment of biomass through cryptobenthic fish assemblages is greatly reduced on Earth’s hottest coral reefs. Extreme environmental conditions, as predicted for the end of the 21st century, could thus disrupt the community structure and productivity of a critical functional group, independent of live coral loss.

Distribution of the acoustic occurrence of dolphins during the summers 2011 to 2015 in the Upper Gulf of California, Mexico.

Baseline knowledge of spatial and temporal distribution patterns is essential for cetacean management and conservation. Such knowledge is particularly important in areas where gillnet fishing occurs, as the Upper Gulf of California, which increases the probability of bycatch of cetaceans. In this area, the vaquita porpoise (Phocoena sinus) has been widely studied, but the knowledge of other cetaceans is scarce and based on traditional visual survey methods. We used data collected by an array of acoustic click detectors (C-PODs) during the summers 2011 to 2015 to analyze the distribution of dolphins in the Vaquita Refuge in the Upper Gulf of California. We recorded 120,038 echolocation click trains of dolphins during 12,371 days of recording effort at 46 sampling sites. Based on simultaneous visual and acoustic data, we estimated a false positive acoustic detection rate of 19.4%. Dolphin acoustic activity varied among sites, with higher activity in the east of the Vaquita Refuge. Acoustic activity was higher at night than during the day. We used negative binomial generalized linear models to study the count of clicks of dolphins in relation to spatial, temporal, physical, biological and anthropogenic explanatory variables. The best model selected for the response variable included sampling site, day-night condition, and vertical component of tide speed. Patterns in the spatial distribution of predicted acoustic activity of dolphins were similar to the acoustic activity observed per sampling season. Higher acoustic activity was predicted at night, but the tide speed variable was not relevant under this condition. Acoustic activity patterns could be related to the availability of prey resources since echolocation click trains are associated with foraging activities of dolphins. This is the first study of the distribution of dolphins in Mexico using medium-term systematic passive acoustic monitoring, and the results can contribute to better management to the natural protected area located in the Upper Gulf of California.

Occupancy Patterns in a Reintroduced Fisher Population during Reestablishment

ABSTRACTMonitoring population performance in the years following species reintroductions is key to assessing population restoration success and evaluating assumptions made in planning species restoration programs. From 2008–2010 we translocated 90 fishers (Pekania pennanti) from British Columbia, Canada, to Washington's Olympic Peninsula, USA, providing the opportunity to evaluate modeling assumptions used to identify the most suitable reintroduction areas in Washington and enhance understanding of fisher habitat associations in the late‐successional forest ecosystems in the coastal Pacific Northwest. From 2013–2016, we deployed 788 motion‐sensing cameras and hair (DNA)‐snaring devices distributed among 263 24‐km2 primary sampling units across the Olympic Peninsula. Our objectives were to determine whether occupancy patterns of the reestablishing population supported assumptions of the initial habitat assessment models, whether the population had expanded or shifted in distribution since the initial reintroductions, compare physical habitat attributes among land‐management designations, and determine whether the founding fishers had successfully reproduced. We predicted that site occupancy by fishers would be associated with landscapes characterized by high proportional coverage of dense forest canopies and medium‐sized and large trees, a diversity of stand structural classes, and area near the administrative boundary separating wilderness from more intensively managed forest lands. We detected fishers across designated wilderness, federal lands outside of wilderness, and other land designations in proportion to land availability on the Peninsula. We found negligible support for predictions that occupancy by fishers was associated with percent forest cover, tree‐size class, or structural class diversity. Rather, occupancy was strongly associated with lands near the wilderness boundary on both sides. We speculate that the boundary between wilderness and more intensively managed forest lands provided fishers with the most suitable prey in proximity to contiguous expanses of low‐ to mid‐elevation late‐successional forests that provided optimal resting, denning, and security values. Occupancy patterns shifted toward the west and south along a precipitation gradient during the study, indicating that population distribution had not yet stabilized 5–8 years following translocation. Genetic results indicated that ≥2 generations of fishers have been produced on the Peninsula. Annual occupancy rates across the Peninsula (0.08–0.24) were lower than in other previously studied and established fisher populations, indicating that not all habitat was fully occupied or that initial estimates of the extent of habitat was overestimated. The strong selection fishers exhibited for wilderness edge and weak selection against extensive forested wilderness areas suggested that habitat managers should strive for maintaining a suitable interspersion of required forest structures and biotic habitat components, such as prey resource availability. © 2019 The Wildlife Society.

Fine-scale foraging behaviour of southern Buller’s albatross, the only Thalassarche that provisions chicks through winter

Predators generally time their reproductive events to match the peak in prey resource availability in order to sustain the elevated energy requirement of offspring provisioning. Consequently, most temperate/polar seabirds breed in spring/summer, including the majority of small albatross species that have short breeding cycles. In contrast, the southern Buller’s albatross Thalassarche bulleri bulleri has a delayed breeding schedule, with chick-rearing extending throughout the entire austral winter. In the present study, the fine-scale at-sea movements and trophic niche of chick-rearing southern Buller’s albatross were determined at Hautere/Solander Island (New Zealand, 46° 35’ S, 166° 54’ E) during the 2016 and 2017 chick-rearing periods to investigate the winter foraging strategy used during this nominally challenging period. The tracks recorded by 15 males (n = 43) and 11 females (n = 21) revealed that foraging behaviour accounted for only a small proportion of time at sea, primarily influenced by the time of day. Foraging occurred mainly in the neritic waters of New Zealand’s South Island shelf, with individuals undertaking consistent short trips (£ 230 km from the colony) or alternating short and long trips up to 1500 km from the colony. Fine-scale tracking data revealed that males spent more time foraging, during shorter trips than females. Their isotopic niches were small, with overlap between sexes, but with males having higher dN values than females. Time spent foraging was influenced by both static and dynamic oceanographic variables. These findings suggest that southern Buller’s albatross foraging behaviour, despite having to sustain chick provisioning in winter, is similar to that of summer-breeding congeners.

Novel pitcher plant-spider mutualism is dependent upon environmental resource abundance.

Positive species interactions are ubiquitous and crucial components of communities, but they are still not well incorporated into established ecological theories. The definitions of facilitation and mutualism overlap, and both are often context dependent. Many interactions that are facilitative under stressful conditions become competitive under more benign ones. This is known as the stress-gradient hypothesis, which is a specific case of context dependency. Stress can be further divided into resource and non-resource categories, but a better mechanistic understanding is necessary to improve the theory's predictions. We examined if two pitcher-dwelling crab spiders (Thomisidae), Thomisus nepenthiphilus and Misumenops nepenthicola, can facilitate nitrogen sequestration in their pitcher plant host, Nepenthes gracilis, by ambushing pitcher-visiting flies and dropping their carcasses into pitchers after consumption. This relationship is, by definition, both mutualistic and facilitative. Laboratory experiments found that both crab spiders increased prey-capture rates of N. gracilis. Nutrient analyses showed that both crab spiders also decreased per unit nitrogen yield of prey. Using experiment duration as a proxy of prey-resource availability, we constructed a mechanistic conceptual model of nutritional benefit. The nutritional benefit received by N. gracilis from T. nepenthiphilus decreases with increasing levels of the limiting resource in the environment (i.e., decreasing levels of resource stress). Our findings suggest that any nutritional mutualism that increases the quantity of resource capture (e.g. number of prey individuals) but decreases the quality of the captured resource (e.g. nitrogen content of individual prey) will necessarily conform to the resource-based predictions of the stress gradient hypothesis.

Intrinsic and extrinsic controls on foraging effort in an iconic Benguela seabird

Abstract Seabirds are upper trophic level predators and as such reflect bottom-up changes in the conditions of their prey species through behavioural or demographic changes. This is especially useful in fisheries management where seabirds can act as biomonitors of commercially-important prey species, potentially providing an attractive, albeit coarse, supplementation to expensive and labour-intensive conventional stock surveys. The Cape gannet Morus capensis is an important predator of both sardine Sardinops sagax and anchovy Engraulis encrasicolus within the Benguela upwelling region, and has been shown to be a useful biomonitor of these fish stocks. A recently-developed automated monitoring system that measures foraging trip durations (a reflection of foraging effort and prey availability) in Cape gannets using VHF technology was used in this study to explore a range of intrinsic and extrinsic drivers of foraging effort that potentially need to be accounted for when relating foraging effort to availability of prey resources. Data from three seasons (2011/2012, 2012/2013 and 2013/2014) representing 5470 foraging trips from 50 chick-provisioning pairs were used for this purpose. Using a linear mixed-effects modelling approach, Cape gannet foraging trip behaviour was shown to be influenced by chick age, parent sex, meteorological conditions (barometric pressure, rainfall and wind) and ambient light conditions. These factors ideally need to be accounted for when foraging effort in seabirds is used as a proxy for prey availability.

Indo-Pacific humpback dolphins (Sousa chinensis) in Hong Kong: Modelling demographic parameters with mark-recapture techniques.

Indo-Pacific humpback dolphins (Sousa chinensis) inhabiting Hong Kong waters are thought to be among the world's most anthropogenically impacted coastal delphinids. We have conducted a 5-year (2010–2014) photo-ID study and performed the first in this region comprehensive mark-recapture analysis applying a suite of open population models and robust design models. Cormack-Jolly-Seber (CJS) models suggested a significant transient effect and seasonal variation in apparent survival probabilities as result of a fluid movement beyond the study area. Given the spatial restrictions of our study, limited by an administrative border, if emigration was to be considered negligible the estimated survival rate of adults was 0.980. Super-population estimates indicated that at least 368 dolphins used Hong Kong waters as part of their range. Closed robust design models suggested an influx of dolphins from winter to summer and increased site fidelity in summer; and outflux, although less prominent, during summer-winter intervals. Abundance estimates in summer (N = 144–231) were higher than that in winter (N = 87–111), corresponding to the availability of prey resources which in Hong Kong waters peaks during summer months. We point out that the current population monitoring strategy used by the Hong Kong authorities is ill-suited for a timely detection of a population change and should be revised.

Understanding resource partitioning in sympatric seabirds living in tropical marine environments

ABSTRACTTwo closely-related species living in sympatry can only coexist if a shift towards a novel ecological niche occurs. For seabird species breeding in tropical regions, competitive pressures intensify due to high population densities in colonies and sporadic prey resources. Here, we used a stable isotope approach to infer inter- and intraspecific variation in foraging behaviour in two congeneric seabird species: Brown Booby (Sula leucogaster, N = 31) and Red-footed Booby (S. sula, N = 30) breeding on Raine Island in the Great Barrier Reef, Australia. Blood (red blood cells and plasma components) and feather samples were collected from breeding birds for δ13C and δ15N analysis. We found significant δ13C interspecific differences in feather and red blood cell tissue, but not in plasma, whereas δ15N values did not differ significantly between species in any of the tissues. Although interspecific differences were small, higher δ13C values found in Brown Boobies suggest differences in foraging strategy between the two species. Inter-sexual differences, either in size or ecology, did not translate into dietary niche segregation. This study suggests that niche-partitioning processes are flexible in the temporal scale, and can be constrained by reproductive behaviour and availability of prey resources.

Return customers: foraging site fidelity and the effect of environmental variability in wide-ranging antarctic fur seals.

Strategies employed by wide-ranging foraging animals involve consideration of habitat quality and predictability and should maximise net energy gain. Fidelity to foraging sites is common in areas of high resource availability or where predictable changes in resource availability occur. However, if resource availability is heterogeneous or unpredictable, as it often is in marine environments, then habitat familiarity may also present ecological benefits to individuals. We examined the winter foraging distribution of female Antarctic fur seals, Arctocephalus gazelle, over four years to assess the degree of foraging site fidelity at two scales; within and between years. On average, between-year fidelity was strong, with most individuals utilising more than half of their annual foraging home range over multiple years. However, fidelity was a bimodal strategy among individuals, with five out of eight animals recording between-year overlap values of greater than 50%, while three animals recorded values of less than 5%. High long-term variance in sea surface temperature, a potential proxy for elevated long-term productivity and prey availability, typified areas of overlap. Within-year foraging site fidelity was weak, indicating that successive trips over the winter target different geographic areas. We suggest that over a season, changes in prey availability are predictable enough for individuals to shift foraging area in response, with limited associated energetic costs. Conversely, over multiple years, the availability of prey resources is less spatially and temporally predictable, increasing the potential costs of shifting foraging area and favouring long-term site fidelity. In a dynamic and patchy environment, multi-year foraging site fidelity may confer a long-term energetic advantage to the individual. Such behaviours that operate at the individual level have evolutionary and ecological implications and are potential drivers of niche specialization and modifiers of intra-specific competition.

Influence of hybridization on animal space use: a case study using coyote range expansion

Hybridization between animal species is likely to increase as distributional and reproductive barriers continue to break down due to anthropogenically driven changes in habitat and climate. Yet, the influence of hybridization on ecological interactions and ecosystem function remains understudied. Animal space use, an important component of ecosystem dynamics, is a complex relationship between intrinsic factors, which hybridization can influence, and extrinsic factors, such as environmental heterogeneity. Using the coyote Canis latrans, a well‐studied species with a long history of hybridization with wolves and dogs Canis spp., we sought to assess the influence of hybridization relative to environmental factors in determining animal space use. We conducted a meta‐regression analysis of 67 datasets on coyote home range size across North America and generated models to predict coyote home range size. Climate (latitude) and environmental variability played important roles in determining patterns of coyote space use, likely through their influence on availability of prey resources. However, we found hybridization to be the preeminent factor driving variation in coyote space use, with non‐introgressed populations having considerably smaller home ranges than those from within the Canis hybrid zone of eastern North America. This pattern was upheld despite the variation in environmental factors between areas inside and outside the Canis hybrid zone. Our findings suggest that hybridization may serve as an important factor affecting ecosystems, as hybrids may have altered space requirements, and presumably different niche dimensions, compared to parental species. This, in turn, may influence the role that particular species play within communities.SynthesisHybridization between animal species is likely to increase due to anthropogenically driven changes in habitat and climate. We used a meta‐regression analysis (n = 67) to examine the relationship between hybridization and coyote Canis latrans space use across North America. We found that independent of environmental factors, introgressed coyotes had larger home ranges. Our findings suggest that hybridization may serve as an important factor affecting ecosystems, as hybrids may have altered space requirements, and presumably different niche dimensions, compared to parental species. This, in turn, may influence the role that particular species play within communities.

Linking resource availability and habitat structure to stream organisms: an experimental and observational assessment

An experiment and a mark‐recapture field study of juvenile coho salmon (Oncorhynchus kisutch) were conducted to identify controls of key energy flow chains in river food webs. In the small‐scale experiment, we investigated the individual and interactive effects of physical habitat structure (PHS) as small wood and resource availability (tissue of adult Chinook salmon, O. tshawytscha) on nutrients, algae, invertebrates, and fish predators including juvenile coho. In the field, we quantified the effects of natural variation in prey availability (invertebrate drift biomass), PHS (wood), and local fish density on summer growth of juvenile coho across multiple stream reaches. Adding salmon tissue to experimental channels resulted in strong bottom‐up effects on select invertebrates including increased population biomass of chironomids and baetids, the numerically dominant invertebrates, and faster growth of juvenile coho. We link the enhanced growth of coho to chironomid productivity: for instance, adult chironomid flux was 4.3× higher and coho consumption of these animals 3× higher in salmon‐subsidized channels. PHS in experimental channels was associated with reduced algal biomass, potentially in response to increased invertebrate consumption, and invertebrate flux or export. The field study revealed coho growth was negatively related to PHS and total fish density and positively related to Diptera drift biomass; however, the effects of fish density and drift biomass on coho growth were relatively weak. The field study also indicated that prey resource availability and coho growth were associated with differences in canopy cover, with prey biomass and coho growth 2–4× higher in reaches receiving more sunlight. As in the experiment, coho in natural stream reaches predominantly fed on adult chironomids and other Diptera, indicating that these taxa and life‐stages are a key link between the benthic food web and mobile vertebrate predators. Our study showed that bottom‐up processes initiated by salmon subsidies and possibly light flux determined key trophic interactions in the Cedar River food web. Moreover, we speculate that PHS may modify some of these interactions indirectly through its effects on the movement of organisms through the environment.

Preface to the special drift foraging issue of Environmental Biology of Fishes

“Imagine a fish feeding in swift water.” With this statement in their landmark foraging model paper, Nicholas Hughes asked the reader to visualize how a driftforaging fish captures its prey (Hughes and Dill 1990). It is a simple, elegant statement, but it captures the essence of stream fish ecology. A stream is defined, after all, as flowing water. Its inhabitants are the product of millennia of adaptations to the unique selective pressures created by this dynamic environment. Imagination is the key for many of us who have studied fish feeding in swift water. It was perhaps Nick’s greatest gift to us. Foraging adaptations, in fact, have for many years led community ecologists to categorize stream fishes by their foraging guilds (e.g. Schlosser 1982). Clearly, stream fish fitness is largely determined by their ability to forage effectively in flowing water. Like all animals, the life histories of stream fishes have been finely tuned by natural selection to capitalize on spatial and temporal availability of prey resources. This truth is so transparent that it is surprising to realize just how under-appreciated it has become in stream fish ecology and management. A survey of the stream fish literature shows howmuch attention is paid to quantifying where fish make their living, versus how little attention is paid to quantifying how they do so. The study of physical habitat in streams has become a sub-discipline of its own, whereas the study of drift foraging has until very recently remained mostly in the realm of ecological theory. Were this a simple academic question it might not be so critical to bring this issue forward. But stream fish management, with its multitude of social and economic implications, has yet to come to grips with the fact that the distribution, growth, and abundance of fish probably depend as much (or more) on food as on space (Chapman 1966). Evolutionary theory, in fact, says as much. Darwin himself suggested that species are shaped more by interactions among themselves (e.g. predators and their prey) than they are by interacting with the physical environment. Animals must acquire resources to grow and reproduce, and those that are most successful enjoy the highest fitness. Thus, restoring natural flow regimes (e.g. Poff et al. 1997) to maintain fish habitat is only half the battle. Without a better mechanistic understanding of how food and space influence fish distribution, growth and abundance, we lack the tools to predict the outcome of habitat change, be it degradation or restoration. We still need an answer to the question that Nicholas posed in the opening lines of Hughes and Dill (1990):

Seasonal influence on the response of the somatotropic axis to nutrient restriction and re‐alimentation in captive Steller sea lions (Eumetopias jubatus)

Fluctuations in availability of prey resources can impede acquisition of sufficient energy for maintenance and growth. By investigating the hormonal mechanisms of the somatotropic axis that link nutrition, fat metabolism, and lean tissue accretion, we can assess the physiological impact of decreased nutrient intake on growth. Further, species that undergo seasonal periods of reduced intake as a part of their normal life history may have a differential seasonal response to nutrient restriction. This experiment evaluated the influence of season and age on the response of the somatotropic axis, including growth hormone (GH), insulin-like growth factor (IGF)-I, and IGF-binding proteins (BP), to reduced nutrient intake and re-alimentation in Steller sea lions. Eight captive females (five juveniles, three sub-adults) were subject to 28-day periods of food restriction, controlled re-feeding, and ad libitum recovery in summer (long-day photoperiod) and winter (short-day photoperiod). Hormone concentrations were insensitive to type of fish fed (low fat pollock vs. high fat herring), but sensitive to energy intake. Body mass, fat, and IGF-I declined, whereas GH and IGFBP-2 increased during feed restriction. Reduced IGF-I and IGFBP with increased GH during controlled re-feeding suggest that animals did not reach positive energy balance until fed ad libitum. Increased IGF-I, IGFBP-2, IGFBP-3, and reduced GH observed in summer reflected seasonal differences in energy partitioning. There was a strong season and age effect in the response to restriction and re-alimentation, indicating that older, larger animals are better able to cope with stress associated with energy deficit, regardless of season.

Effects of Shoreline Modifications on Supratidal Macroinvertebrate Fauna on Puget Sound, Washington Beaches

In coastal environments, the supratidal zone bridges marine and terrestrial ecosystems and is important for energy exchange. However, it is also subject to extensive anthropogenic disturbance, such as armoring of shorelines. Shoreline armoring is extensive along many coasts, but the impacts on biota are comparatively unknown. Between 2000 and 2002, paired and synoptic sampling regimes were employed to assess armoring effects on insects and benthic macroinvertebrates in the supratidal zone of Puget Sound beaches. Paired sampling showed natural beach sites had significantly more deposited wrack. Infauna was dominated by oligochaetes and nematodes; talitrid amphipods, insects, and collembolans were significantly more numerous at natural beaches, and crustaceans were more abundant at altered beaches. Insect assemblages were diverse, with taxon richness higher at natural beach sites. In the synoptic sampling, where sites with higher elevation modifications were used, there were fewer differences in invertebrate assemblages between armored and nonarmored sites. The results show that, where shoreline armoring lowers the land–sea interface, benthic infauna and insect assemblages are disrupted. Widespread shoreline modifications may decrease the availability of prey resources for fish and wildlife and decrease the contribution of organic material entering the nearshore ecosystem.

Feeding tactics of a behaviorally plastic predator, summer flounder ( Paralichthys dentatus)

In a series of laboratory experiments, the feeding behaviors of summer flounder ( Paralichthys dentatus) were examined in response to squid and fish prey. Attack and capture tactics were evaluated for their influence on capture success, handling time, and prey-type selectivity. The ambush tactic was the primary behavior (50.6%) used to attack squid. Secondary attack types included active pursuit (42.7%) and stalking (6.7%). Regardless of the prey species targeted or the type of attack employed, summer flounder were equally efficient in capturing prey; capture success rates ranged from 50%–83%. The majority of prey were swallowed in a headfirst orientation (55.3% of squid), however swallow alignment did not significantly affect handling time. Approach times during ambush attacks were greater overall in comparison to active attacks, and relative prey size significantly affected capture times. Despite additional costs in handling time, summer flounder actively selected for mummichogs ( Fundulus spp.) (attack rate (attacks per minute) = 0.11) over longfin squid ( Loligo pealeii) (0.08) and Atlantic silversides ( Menidia menidia) (0.02). Differential attack rates favoring mummichogs suggests a preference towards demersal prey. In the presence of relatively large, fast-moving, and pelagic prey, summer flounder used a greater diversity of attack tactics than have been observed previously under controlled conditions. The behavioral plasticity exhibited by summer flounder is likely mediated by prey behavior and local availability of prey resources in inshore and offshore environments.

Diversity of Forest Litter-Inhabiting Ants Along Elevations in the Wayanad Region of the Western Ghats

Litter ant diversity and abundance in relation to biotic and abiotic factors were analyzed at five primary forest sites lying between 300 to 1650 meter above mean sea level in the Wayanad region of the Western Ghats in Kerala, southern India. Ant abundance and species richness peaked at mid-elevations influenced by the presence of favourable physical conditions and abundance of prey resources. Dominance of ants preferring termites and Collembola as prey at sites rich in their specific prey resources indicate the influence of local prey resource availability in determining ant distribution. Dominant species (Tapinoma sp. and Solenopsis sp.) had wider distributions, being present at all elevations. Physical factors (slope of the terrain, rainfall, moisture, humidity, temperature) and prey resource availability (insect larvae, termites, Collembola) influenced ant species abundance at a regional scale, whereas at local scales, site specific variations in the relationship between abundance of ants and prey-predators and physical factors were recorded. The present study highlights the need to consider site-specific abiotic and biotic factors while examining the distribution patterns of litter ants along altitudinal gradients in other regions of the Western Ghats, which is a recognised hot spot of biodiversity with wide regional variation in vegetation types and faunal distribution patterns.

A potential habitat network for the Eurasian lynx Lynx lynx in Scotland

ABSTRACT The severe and early destruction and fragmentation of woodland habitats due to human activities is thought to have been a leading factor in the extirpation from Britain of several large, forest‐dependent mammal species, such as the Eurasian lynx Lynx lynx. However, during the 20th century, Scotland in particular has experienced rapid, large‐scale reafforestation. In order to assess if this reafforestation has been sufficient to permit the potential restoration of extirpated forest mammal species with large spatial requirements, a Geographical Information System (GIS) analysis of potential habitat of one species, the Eurasian lynx, was performed for the Scottish mainland. A rule‐based analysis, incorporating data and expert opinion from Switzerland, an environmentally similar area where lynx now occur, was used to identify patches of suitable lynx habitat in Scotland. A connectivity analysis was used to investigate whether and how these patches are connected to form larger interconnected networks of potential lynx habitat that would allow lynx to sufficiently interact with one another to form a single interbreeding population. Scotland has over 20 000 km2 of suitable lynx habitat split into two main networks of interconnected patches: the Highlands (c. 15 000 km2) and the Southern Uplands (c. 5000 km2). A further 800 km2 of potential habitat, contiguous with the Southern Uplands lynx habitat network, lies across the border in England. Although connectivity between the Highlands and Southern Uplands networks is currently weak, the implementation of measures to mitigate the barrier effects of busy roads in central Scotland could facilitate the movement of lynx between the two areas. Based on the availability of prey resources, Scotland could support around 400 adult and subadult lynx in the Highlands and around 50 in the Southern Uplands. A Scottish population of this size would be the fourth largest lynx population in Europe considering current population estimates.

Availability of prey resources drives evolution of predator-prey interaction.

Productivity is predicted to drive the ecological and evolutionary dynamics of predator-prey interaction through changes in resource allocation between different traits. Here we report results of an evolutionary experiment where prey bacteria Serratia marcescens was exposed to predatory protozoa Tetrahymena thermophila in low- and high-resource environments for approximately 2400 prey generations. Predation generally increased prey allocation to defence and caused prey selection lines to become more diverse. On average, prey became most defensive in the high-resource environment and suffered from reduced resource use ability more in the low-resource environment. As a result, the evolution of stronger prey defence in the high-resource environment led to a strong decrease in predator-to-prey ratio. Predation increased temporal variability of populations and traits of prey. However, this destabilizing effect was less pronounced in the high-resource environment. Our results demonstrate that prey resource availability can shape the trade-off allocation of prey traits, which in turn affects multiple properties of the evolving predator-prey system.