Prey Vulnerability Research Articles

Environmental factors regulate occupancy of free-ranging dogs on a sub-Antarctic island, Chile

Domestic dogs (Canis familiaris) are the most common carnivore species in natural ecosystems worldwide. They are of considerable concern for wildlife conservation, particularly in the absence of predators. However, we are only beginning to understand the ecology of free-ranging dogs, and even less is known in sub-Antarctic environments. Here, we used camera-trap data to assess space use of free-ranging dogs on a sub-Antarctic island in the Cape Horn Biosphere Reserve, southern Chile, which lacks native terrestrial carnivores. We predicted free-ranging dogs to be associated with human settlements, trails, and roads and to prefer open habitats over forest for the ease of movement. We obtained 67 independent dog records of 62 individuals over 3909 camera-trap days from 200 sites. Single-species single-season occupancy models revealed that both rural/village dogs, as well as putative feral dogs chose peatbogs over forest, but their preference for settlements and roads was less pronounced and inconsistent among dog categories. Our findings revealed evidence for a reproducing feral dog population on Navarino Island that may be sustained by recruits from rural/village dogs, as identical sites were visited by both dog categories. However, due to a higher occupancy with proximity to human dwellings, the dependence of feral dogs on human resources remain uncontested. In light of the penetration of dogs into pristine sub-Antarctic habitats and their possible impacts on native vulnerable prey, we recommend the implementation of responsible pet-ownership regulations, as well as ethically-approved control actions for feral dogs to protect one of the planet’s last wilderness areas.

The eco-evolutionary dynamics of a predator-prey system across an r/K continuum

The effects of a single trait on more than one ecological function is called ecological pleiotropy. Traits that exhibit ecological pleiotropy are relevant to eco-evolutionary dynamics because the structure of interaction between the trait and its ecological functions alters how eco-evolutionary feedback loops emerge. Density-dependent selection (DDS) assumes that a single trait affects both density-independent and density-dependent population growth through ecological pleiotropy, and is one of the simplest routes for feedback loops. The r/K theory proposes a mechanism by which DDS occurs, but its predictions were poorly explored in an eco-evolutionary context. Some assumptions of the r/K theory seems to be relevant for the eco-evolution of predator-prey interactions. However, the relationship between these theories were poorly explored. Here, we investigate how does the r/K theory relates to the eco-evolution of predator-prey systems. We seek to answer two questions: (1) What are the system’s parameters that affect the predominance of r- and K-selection? (2) Does system’s qualitative behaviour depends on whether the predominant selection on prey population is an r- or a K-selection? To answer these questions, we built a model of differential equations describing the eco-evolutionary dynamics of a predator-prey system. We assume that prey vulnerability to predation is an adaptive trait that affects preys density-dependent growth rate through ecological pleiotropy. Then, we partitioned the selection gradient in its r- and K-selection components and evaluate how their magnitude relates to systems behaviour. We found that stable predator-prey cycles only occurs when K-selection is predominant. When r-selection is predominant, cycles lead to a runaway dynamics. Furthermore, the way predators parameters affect prey position in the r/K continuum depends on how they affect predation risk. While increasing predation risk increases K-selection, decreasing it increases r-selection. We discuss the relevance of the structure of ecological pleiotropy to our results and the perspectives that unifies the r/K theory and eco-evolutionary dynamics.

Foraging behaviour of four avian species feeding on the same temporarily available prey

Low tide events provide terrestrial predators with ephemeral, but predictable and abundant sources of prey. Understanding the relationships between tidal cycles, prey availability, and predator abundances is vital to characterizing the ecological relationship between terrestrial predators and their marine prey. Here, we describe the foraging tactics of four common bird species in western North America — Bald Eagles (Haliaeetus leucocephalus (Linnaeus, 1766)), Great Blue Herons (Ardea herodias Linnaeus, 1758), Glaucous-winged Gulls (Larus glaucescens J.F. Naumann, 1840), and Northwestern Crows (Corvus caurinus S.F. Baird, 1858) — feeding on the same transiently accessible fish species, the plainfin midshipman (Porichthys notatus Girard, 1854). We conducted avian predator surveys at breeding beaches of plainfin midshipman across multiple years and sites. Our census data showed that Bald Eagle and Great Blue Heron abundances were higher when the tides were receding than incoming at Ladysmith Harbour, British Columbia, Canada, but the opposite trend was found for total predator abundance at a second site in Dabob Bay, Washington, USA. Glaucous-winged Gull abundance decreased over the course of the plainfin midshipman breeding season (April–July), whereas the abundances of the other three species remained stable. Our data suggest that the foraging activities of birds in the intertidal zones of western North America are linked with the tidal cycles, corresponding to periods of high prey vulnerability.

From wheel of fortune to wheel of misfortune: Financial crises, cycles, and consumer predation

AbstractPredator–prey dynamics are widely used in ecology but seldom utilized in economics and marketing, despite their ability to express financial market agents' behaviors when considered in combination with economic cycles and financial crises. This multidisciplinary article presents a stylized framework of a market cycle that combines the notions of supply and demand and predator–prey interactions between buyers and sellers of housing mortgages. We illustrate our framework using data from the Global Financial Crisis and a Lotka‐Volterra predator–prey model. We find that with our framework we can capture the dynamics of the market, particularly the peak and decline in the number of sellers and sold subprime mortgages. Our framework sheds a new light on consumer behaviors, pinpointing how they can put themselves into vulnerable prey positions. This article is one of the first of its kind to propose market phases and predator–prey dynamics nested in economic cycles and consumer buying trends.

Invasive mammalian predators habituate to and generalize avian prey cues: a mechanism for conserving native prey.

Invasive mammalian predators can cause the decline and extinction of vulnerable native species. Many invasive mammalian predators are dietary generalists that hunt a variety of prey. These predators often rely upon olfaction when foraging, particularly at night. Little is understood about how prey odor cues are used to inform foraging decisions. Prey cues can vary spatially and temporally in their association with prey and can either reveal the location of prey or lead to unsuccessful foraging. Here we examine how two wild-caught invasive mammalian bird predator species (European hedgehogs Erinaceus europaeus and ferrets Mustela putorius furo) respond to unrewarded bird odors over successive exposures, first demonstrating that the odors are perceptually different using house mice (Mus musculus) as a biological olfactometer. We aim to test if introduced predators categorize odor cues of similar prey together, a tactic that could increase foraging efficiency. We exposed house mice to the odors using a standard habituation/dishabituation test in a laboratory setting, and wild-caught European hedgehogs and ferrets in an outdoor enclosure using a similar procedure. Mice discriminated among all bird odors presented, showing more interest in chicken odor than quail or gull odor. Both predator species showed a decline in interest toward unrewarded prey odor (i.e., habituation), but only ferrets generalized their response from one unrewarded bird odor to another bird odor. Hedgehog responses to unrewarded bird odors were highly variable between individuals. Taken together, our results reveal interspecific and intraspecific differences in response to prey odors, which we argue are a consequence of different diet breadth, life and evolutionary histories, and the conditions in each experiment. Generalization of prey odors may have enabled some species of invasive predators to efficiently hunt a range of intraguild prey species, for example, ground-nesting shorebirds. Olfactory manipulation of predators may be a useful conservation tool for threatened prey if it reduces the conspicuousness of vulnerable prey.

Exploring Temporal Variability in the Southern Benguela Ecosystem Over the Past Four Decades Using a Time-Dynamic Ecosystem Model

This paper presents a new, updated, temporally-dynamic Ecosim model for the Southern Benguela (1978-2015) by capturing recent advancements in our understanding of the dynamics and newly available data series from an additional decade of research in the region. The paper documents the model development and the thinking behind incorporating a newly available upwelling index, and observed fishing effort as important drivers of modelled ecosystem dynamics. The most sensitive predator-prey interactions were identified and vulnerabilities (of prey to predators) were estimated to improve model fit to field observations under each scenario. Sardine interactions with prey and predators were consistently found to be sensitive interactions in model fitting, accounting for at least 40% of the most sensitive trophic interactions in the southern Benguela modelled food web. Model fits to data were improved by a total of 85% reduction in sum of squares when upwelling effects on large phytoplankton availability to zooplankton and small pelagic fish was incorporated, geographic shifts in sardine distribution were captured by means of altered availability of sardine to predators, corresponding vulnerabilities of prey to predators were estimated, and an additional, small, hypothetical forcing function was fitted to small phytoplankton production. African penguin and Cape gannet fits to data series were improved by incorporating a recently published bird Food Availability Index, although model fits of several fish groups then deteriorated, emphasising the need for additional empirical species-specific functional response studies. Attempts at fitting the full area model to either west coast or south coast time series did not improve overall model fits, highlighting limitations of the current non-spatialized model in describing coast-specific dynamics. This study shows promise in unravelling the observed dynamics of the Benguela upwelling ecosystem, and points to the importance of exploring spatially disaggregated approaches, in particular the new foraging habitat capacity of the Ecospace approach, to improve our understanding of processes whereby variability in upwelling influences dynamics of the Southern Benguela ecosystem. This is important in reconciling knowledge needed to manage fisheries and to protect marine biodiversity by means of ecosystem-based management in South Africa, and to advance management advice under future scenarios of climate change.

Prey vulnerability and predation pressure shape predator-induced changes in O2 consumption and antipredator behaviour

Predators regulate prey abundance (direct predation) as well as influencing their metabolism and behaviour (indirect effects) through the perception of risk. Antipredator traits are informed by individual experience of risk, which may vary over environmental gradients and through ontogeny. As prey grow, individual vulnerability generally diminishes, and the reduction in individual vulnerability with ontogenetic growth can potentially lead to size refugia, ultimately nullifying the impacts of direct predation. Despite the ecological importance of the indirect effects of predation and the disproportionate influence larger individuals have on ecological level processes, there has been little focus on the potential indirect effects of predation risk on invulnerable prey. Using a combination of field and laboratory experiments, we measured the changes in routine oxygen consumption of vulnerable and invulnerable size classes of the intertidal snail Nucella lapillus (dogwhelk), exposed to effluent from its crab predator Carcinus maenas. To test the potential influence of prior experience of predation risk, measurements were conducted on populations naturally exposed to different levels of predation pressure. Field results showed that only invulnerable snails modified their routine oxygen consumption in the presence of risk, and this occurred across all populations. Oxygen consumption rates in the laboratory, however, contradicted the pattern, with only vulnerable prey responding to the perception of risk. Metabolic responses of both vulnerable and invulnerable prey under field and laboratory conditions are discussed in the context of asset protection and prey energetic state. Observations of snail behaviour in the laboratory showed that dogwhelks from exposed shores, where predatory risk is higher, were more likely to exhibit antipredator behaviour. Importantly, our findings provide evidence that the indirect effects of predators remain influential even after prey are no longer susceptible to direct predation and add to the growing body of evidence highlighting the ecological importance of indirect predation.

Predictors of puma occupancy indicate prey vulnerability is more important than prey availability in a highly fragmented landscape

Habitat fragmentation represents the single greatest conservation challenge of the 21st century. This problem is particularly acute for large, obligate carnivores like pumas Puma concolor which have persisted in North and South America in the face of habitat fragmentation and other anthropogenic disturbances. Shrinking habitat and reduced connectivity mean that mapping habitat is increasingly important for species conservation in multiple-use landscapes. Previous work suggests that pumas occupy habitats where sufficient stalking cover and preferred prey are present, yet the intersection of these factors has rarely been assessed. Here we used data from 68 299 camera trap nights collected from 181 sites throughout the San Francisco Bay Area over a four-year period to identify key predictors of habitat occupancy for pumas and their primary prey (mule deer Odocoileus hemionus). Our goal was to determine whether pumas occupy habitats based on relative measures of prey availability (detection frequency), or ease of predation (density of stalking cover) and whether these predictors changed between seasons. Our results indicated that pumas primarily occupied forested habitats and did not choose habitats with abundant deer. Instead, pumas preferentially occupy habitats that facilitate their stalk and ambush hunting strategy, rather than higher prey densities, per se. The best occupancy models for mule deer indicated the importance of roads and shrub cover. However, even the best deer models performed poorly compared to the puma models, likely due to the ubiquity of mule deer in the region. Although prey density is a widely accepted correlate of habitat quality for many carnivores, our results suggest that structural elements of habitat may be a more important variable in predicting habitat use by large stalk and ambush predators like pumas, which has important implications for conservation success.

Native Gammarus fossarum affects species composition of macroinvertebrate communities: evidence from laboratory, field enclosures, and natural habitat

Despite the fact that native species of amphipods have been recognized as active predators similarly to invasive species, little is known about their predatory impact on aquatic communities. In this study, we used a laboratory experiment, a field enclosure experiment, and an analysis of natural community data to demonstrate how Gammarus fossarum affects the species composition of benthic communities by imposing survival selection on its prey. Our laboratory single-prey experiment brought a clear evidence that tube-less chironomids are vulnerable prey and that the predation rate on the tube-dwelling chironomids decreases with increasing tube toughness (from the soft tubes made of detritus to the hard tubes made of sand or calcium carbonate grains). We found that the introduction of G. fossarum to field enclosures significantly changed the species composition of a macroinvertebrate community at an experimental spring fen site. The soft-bodied, slow moving, and tube-less taxa were depleted the most. It appears that the observed patterns were a result of predator’s preference rather than encounter rate. Survival selection was detected also in natural communities across a large spatial scale. In accordance with the experiments, high densities of G. fossarum limited the proportion or abundance of vulnerable prey. Our study (1) provides the first convincing evidence that biotic interactions have a structuring effect on the spring fen communities, (2) documents how the predatory effect in a community depends on an interplay between the prey handling behaviour of the predator and species-specific susceptibility of prey, and (3) shows that an omnivorous native amphipod may have a strong impact on aquatic communities despite it is regarded less aggressive than its invasive relatives.

Is cat hunting by Indigenous tracking experts an effective way to reduce cat impacts on threatened species?

Abstract ContextFeral cat is a favoured food item in some Australian Indigenous communities. We describe how cats are hunted and whether cat hunting can contribute to the persistence of threatened species. AimsTo determine whether cat hunting by expert trackers has the potential to be an effective method of managing predation impacts on threatened species at key sites. MethodsWe recorded all cats captured on the Kiwirrkurra Indigenous protected area (Kiwirrkurra IPA) over a 5-year period by offering incentive payments for hunters to report their catch. For a subset of hunts, we measured the duration and distance of the hunt. We compared the frequency of occurrence of cat tracks in 2-ha track plots between the hunting zone and more remote, unmanaged areas. At a finer scale, we compared cat presence at bilby burrows inside and outside the hunting zone. Key resultsIn all, 130 cats were removed from the Kiwirrkurra IPA from 2014 to 2019. Hunts took an average of 62min to complete and a team of four hunters could catch up to four cats in a single day. Although cats still occurred throughout the hunting zone, we found that cat detections at track plots were less likely in the areas where cats were hunted. Long-term data suggest that threatened species have persisted better in areas where there is an active presence of hunters. ConclusionsCat hunting by Indigenous tracking experts is an efficient method of despatching cats at localised sites. Following footprints on foot facilitates the targeting of individual cats that are hunting at threatened species burrows. More rigorous studies are required to determine whether cat hunting significantly reduces predation on threatened species, or whether there are other co-benefits of maintaining a presence of hunters in the landscape (such as fine-scale fire management) that are more important for the persistence of vulnerable prey. Implications Wherever open sandy substrates occur, there is potential to employ Indigenous expert trackers to assist with the removal of problem cats, such as, for example, to complete cat eradication inside fenced reintroduction sites, or at times of peak prey vulnerability, such as breeding events or after bushfires.

Habitat modification effects on anuran food webs in the Colombian tropical dry forest

Habitat loss and transformation are major threats to biodiversity and ecosystem functioning, but their effects on species interaction are often poorly understood. We evaluated effects of habitat transformation and seasonality on anuran-prey food webs in Colombian dry-forests. We asked whether anthropic transformation (anthropic vs natural) and/or seasonality (dry, minor and major rain seasons) affect predator load on arthropods, the occurrence of energetic bottlenecks, and the diet overlap of anurans. We selected six dry forest sites in the Caribbean of Colombia, sampled anurans, and identified their stomach contents to construct anuran-prey food webs. We show that the global structure of food webs was affected by disturbance and seasonality, but not by their interaction. Prey vulnerability was higher in anthropic habitats. Habitat transformation enhanced diet overlap among predators, but there was not a differential effect of habitat type according to seasonality for network metrics. Our study shows a strong effect of natural vegetation modification in tropical dry forest on anuran-prey food webs, while seasonality did not seem to further mediate these effects.

Paradoxes of vulnerability to predation in biological dynamics and mediate versus immediate causality

<p style='text-indent:20px;'>The causality scheme of an (essentially non symmetric) predator-prey system involves automaticaly advantages and disadvantages highly dependent on time. We study systems with one predator and one or two preys furnishing issues which involve mediate and inmediate causality (naturally associated with the attractor and the previous transient). The issues are highly dependent on the parameter accounting for the vulnerability of the preys. When the vulnerability is small, an increase of it implies a (demographic) disadvantage for the preys, but, when it is large (involving periodic cycles) an increase turnes out in an advantage because of the rarefaction of predators (this is associated with average populations on the periodic cycles). When two preys with different vulnerability are present, the most vulnerable may desappear (i. e. the attractor does not contain such prey). This phenomenon only occurs when the less vulnerable prey is nevertheless able to support the predator; otherwise, this one keeps eating anyway the other preys. The mechanism of such patterns are better described in terms of attractors and stability than in terms of advantages versus disadvantages (which are drastically dependent on the viewpoints of the three species).

Mangroves reduce the vulnerability of coral reef fisheries to habitat degradation.

Despite general and wide-ranging negative effects of coral reef degradation on reef communities, hope might exist for reef-associated predators that use nursery habitats. When reef structural complexity is lost, refuge density declines and prey vulnerability increases. Here, we explore whether the presence of nursery habitats can promote high predator productivity on degraded reefs by mitigating the costs of increased vulnerability in early life, whilst allowing for the benefits of increased food availability in adulthood. We apply size-based ecosystem models of coral reefs with high and low structural complexity to predict fish biomass and productivity in the presence and absence of mangrove nurseries. Our scenarios allow us to elucidate the interacting effects of refuge availability and ontogenetic habitat shifts for fisheries productivity. We find that low complexity, degraded reefs with nurseries can support fisheries productivity that is equal to or greater than that in complex reefs that lack nurseries. We compare and validate model predictions with field data from Belize. Our results should inform reef fisheries management strategies and protected areas now and into the future.

Status and Magnitude of Grey Wolf Conflict with Pastoral Communities in the Foothills of the Hindu Kush Region of Pakistan.

Simple SummaryDespite higher loss due to disease, human–carnivore conflicts over livestock depredation is one of the major problems in carnivore conservation, both locally and globally. Locals share negative attitudes towards the wolf due to conflicts over livestock depredation. Using semi-structured questionnaires, we found that grey wolf is in a serious conflict with the locals, causing economic loss to them at the expanse of its own life. The locals considered the species a serious threat to their livestock, causing them economic losses, and wanted to reduce or even eliminate it from their area. Respondents having larger herd size and higher dependency on livestock for earning livelihoods shared more negative attitudes towards the wolves. In our study area the economic loss of the locals due to livestock mortalities from diseases was higher than that from wolf depredation. Therefore, we suggested that vaccination of the livestock and compensation schemes will help to change the perception of locals towards wolf.Pastoralist–wolf conflict over livestock depredation is the main factor affecting conservation of grey wolf worldwide. Very limited research has been carried out to evaluate the pattern and nature of livestock depredation by wolf. This study aims to determine the status and nature of human–wolf conflict across different villages in the Hind Kush region of Pakistan during the period January 2016–December 2016. For this purpose, a total of 110 local male respondents from all walks of life were interviewed using a semi-structured questionnaire. The grey wolf was declared as a common species in the area by 51.3% of the locals with an annual sighting rate of 0.46 each. During the year (2016), a total of 358 livestock were lost to grey wolf predation and disease. Of the total livestock loss, grey wolf was held responsible for a total 101 livestock losses. Goat and sheep were the most vulnerable prey species as they accounted for 80 (79.2%) of the total reported depredations. Out of the total economic loss (USD 46,736, USD 424.87/household), grey wolf was accountable for USD 11,910 (USD 108.27 per household), while disease contributed 34,826 (USD 316.6 per household). High depredation was observed during the summer season 58.42% (n = 59) followed by spring and autumn. Unattended livestock were more prone to grey wolf attack during free grazing in forests. Most of the respondents (75.45%) showed aggressive and negative attitudes towards grey wolf. The herders shared more negative attitude (z = −3.21, p = 0.001) than businessman towards the species. Herders having larger herd size displayed more deleterious behavior towards wolves than those having smaller herd size. Active herding techniques, vaccinating livestock, educating locals about wildlife importance, and initiating compensating schemes for affected families could be helpful to decrease negative perceptions.

Simulated elephant-induced habitat changes can create dynamic landscapes of fear

Landscapes of fear have become widely studied in the northern hemisphere, but are still largely understudied in the more complex, diverse carnivore-prey communities of Africa. Habitat changes brought about by a megaherbivore, the African elephant (Loxodonta africana), can modify the perceived landscape of fear by predation vulnerable prey species (impala Aepyceros melampus and warthog Phacochoerus africanus) in contrast with non-prey species (white rhinoceros Ceratotherium simum). We hypothesized that by opening up woody vegetation, elephants may modify perceived risk at a landscape-scale, but also at a fine scale by depositing escape impediments in the form of coarse woody debris. We experimentally tested this in Hluhluwe-iMfolozi Park, South Africa, by simulating elephant-induced habitat changes on patch scale (opening up woody vegetation) and within-patch scale (deposition of coarse woody debris) and monitoring the herbivore visitation using camera traps. We compared visitation on the edge of grazing lawns (in proximity of dense vegetation) and the centre (open, highly visible patches), either with or without coarse woody debris and with or without fresh predator scat. We found that mesoherbivore prey species showed contrasting responses, with warthog avoiding plots close to dense vegetation and plots with coarse woody debris. Impala reduced their visitation to dense vegetation patches only during risky times, at night, especially in the presence of predator scat, but did not clearly avoid plots with coarse woody debris. Our study indicates that, in African savannas, the perceived landscape of fear is a highly dynamic phenomenon varying in both space and time and being species-specific. Elephant induced habitat changes may shape landscapes of fear in complex and contrasting ways.

Cracking the cuisine: Invasive European shore crabs (Carcinus maenas) select a menu of soft-shelled mussels over cockles

The European shore crab, Carcinus maenas, is known to feed extensively on a variety of benthic species, and can affect commercially important bivalve fisheries. As a marine invasive species, predation by C. maenas can have ecological and commercial effects in its non-native range. We investigated potential predatory effects of non-indigenous C. maenas on native bivalves, and if shell strength of bivalve prey influenced predation susceptibility. The main prey species tested were ecosystem-engineering mussels (Mytilidae, Xenostrobus inconstans), and commercially valuable mud cockles (Veneridae, Katelysia peronii.). In separate field experiments, crabs were offered either a choice between both bivalve species or non-choice for each species separately. Male and female crabs equally consumed mussels across both choice and non-choice experiments. The proportion of cockles consumed was significantly lower than that of mussels in choice experiments, and no cockles were consumed in the non-choice experiment. Bivalve compressive shell strengths were tested separately with a universal testing machine. The breaking force required to crush shells of adult K. peronii was much higher than the claw strength of adult crabs, but the significantly lower shell-breaking forces required for X. inconstans make the mussels vulnerable prey. Additional compressive shell strength tests on other native bivalve species and juvenile Katelysia showed that they were susceptible to crab predation. Results indicate that predation by non-indigenous C. maenas on soft-shelled mussels and juvenile cockles could impact native bivalve abundances. Shell strength measurements of potential prey are a suitable approach to assess the risk for ecological and economic impacts of this globally invasive crab.

Bovid mortality patterns from Kanjera South, Homa Peninsula, Kenya and FLK-Zinj, Olduvai Gorge, Tanzania: Evidence for habitat mediated variability in Oldowan hominin hunting and scavenging behavior

The archaeological record has documented Oldowan hominin occupation of habitats ranging from open grasslands to riparian forest by 2.0 Ma. Despite this we have a poor understanding of whether hominin foraging behavior varied in different environmental settings. We compared bovid mortality profiles from the two largest Oldowan zooarchaeological samples, one from a grassland (Excavation 1, Kanjera South, Kenya) and another from a woodland (FLK Zinj, Olduvai Gorge, Tanzania) with bovid mortality samples created by African carnivores in different habitats. Kanjera hominins frequently had early access, likely through hunting, to small (size 1 ≤ 23 kg and size 2 = 24–112 kg) juvenile bovids, creating a mortality pattern similar to that created by grassland dwelling carnivores. Kanjera hominins had more mixed access to large (size 3 = 113–340 kg), often juvenile, bovids and frequently scavenged heads. In contrast, previous work has shown that the few small bovids at FLK-Zinj were predominantly older individuals. Prime adults dominated the FLK-Zinj large bovid sample, leading to a mortality pattern similar to that created by carnivores occupying more closed habitats. Variation in bovid body size and mortality profiles between these archaeological assemblages may reflect the challenges of acquiring fauna in open versus closed habitats with a simple hunting toolkit. The heterogeneous woodland habitat of FLK-Zinj would have provided more opportunities to ambush prey, whereas on grasslands with more limited concealment opportunities Kanjera hominins focused their efforts on vulnerable juvenile prey, some likely acquired after short chases.

FOOD WEB STRUCTURE BUT NOT ROBUSTNESS DIFFER BETWEEN RIVERS, LAKES AND ESTUARIES

The pervading physical habitat differences between lakes, rivers, and estuaries should result in structural and thus stability differences in food webs in these three different aquatic habitats. We compared 24 metrics of food web structure and the robustness to loss of both well-connected and random species of 18 well-resolved food webs from six lakes, six rivers, and six estuaries. Robustness measures the proportion of species that need to be removed for 50% of all species to be lost/disconnected. Riverine food webs had lower neighborhood clustering and greater variability in prey vulnerability than estuaries and lakes. Typically, rivers experience physical disturbance relatively more frequently and with greater severity than estuaries and lakes. Disturbance may drive rivers to have lower clustering and have greater proportions of early successional taxa that are mobile and have little armor, and hence greater variability in their vulnerability to predation. Despite the observed differences in food web structure, these did not drive differences in modelled food web robustness between the three habitats. Similarities in robustness may be a result of freshwater organisms having similar body-size ratios between predator and prey/resource taxa thereby driving similar link distributions.

Top–down limits on prey populations may be more severe in larger prey species, despite having fewer predators

Variation in the vulnerability of herbivore prey to predation is linked to body size, yet whether this relationship is size‐nested or size‐partitioned remains debated. If size‐partitioned, predators would be focused on prey within their preferred prey size range. If size‐nested, smaller prey species should become increasingly more vulnerable because increasingly more predators are capable of catching them. Yet, whether either of these strategies manifests in top–down prey population limitation would depend both on the number of potential predator species as well as the total mortality imposed. Here we use a rare ecosystem scale ‘natural experiment’ comparing prey population dynamics between a period of intense predator persecution and hence low predator densities and a period of active predator protection and population recovery. We use three decades of data on herbivore abundance and distribution to test the role of predation as a mechanism of population limitation among prey species that vary widely in body size. Notably, we test this within one of the few remaining systems where a near‐full suite of megaherbivores occur in high density and are thus able to include a thirtyfold range in herbivore body size gradient. We test whether top–down limitation on prey species of particular body size leads to compositional shifts in the mammalian herbivore community. Our results support both size‐nested and size‐partitioning predation but suggest that the relative top–down limiting impact on prey populations may be more severe for intermediate sized species, despite having fewer predators than small species. In addition we show that the gradual recovery of predator populations shifted the herbivore community assemblage towards large‐bodied species and has led to a community that is strongly dominated by large herbivore biomass.

Modeling potential impacts of three benthic invasive species on the Lake Erie food web

Assessing the potential for aquatic invasive species (AIS) to impact ecosystem function and services is an important component of ecological risk assessment. This study focuses on quantifying changes in biomass of food web groups in response to changes in AIS biomass as a function of variable AIS prey vulnerabilities (i.e. food availability) and AIS vulnerabilities to predators (i.e. predation pressure). We modified an existing Lake Erie food web model to assess the potential food web impacts of three benthic AIS (Eurasian ruffe Gymnocephalus cernua, killer shrimp Dikerogammarus villosus, and golden mussel Limnoperna fortunei) that may invade Lake Erie in the near future. Simulated biomass of golden mussels was most affected by bottom-up control, while killer shrimp and ruffe were affected by both top-down and bottom-up controls. AIS food web impacts showed both monotonic and non-monotonic responses to AIS biomass. Impacts from ruffe were highest when their biomass was high, while killer shrimp and golden mussels had maximal impacts at intermediate biomass levels on some food web groups. Our results suggest that golden mussels, which can feed at a lower trophic level and have fewer predators than ruffe or killer shrimp, may reach much higher equilibrium biomass under some scenarios and affect a broader range of food web groups. While all three species may induce negative effects if introduced to Lake Erie, golden mussels may pose the highest risk of impact for Lake Erie’s food web.