Carcass size shapes the structure and functioning of an African scavenging assemblage

The particle size of the food resource strongly determines the structure and dynamics of food webs. However, the ecological implications of carcass size variation for scavenging networks structure and functioning have been largely overlooked. Here we investigate differences in scavenging patterns due to carcass size in a complex vertebrate scavenger community, Hluhluwe‐iMfolozi Park, South Africa, while taking into account seasonality. We monitored the consumption of three types of experimental carcasses: ‘small’ (< 10 kg), ‘medium’ (10–100 kg) and ‘large’ (> 100 kg). We employed general lineal models to explore the influence of carcass size on 1) scavenging network structure (scavenger species richness per carcass) and 2) functioning (carcass detection time, consumption time, consumption rate and percentage of carrion consumed). We also tested whether the structure of the scavenging network of each carcass size was nested, i.e. whether the scavenging assemblage in species‐poor carcasses was a subset of the assemblage consuming species‐rich carcasses. We found strong evidence indicating that carcass size is a major factor governing the associated scavenger assemblage. Scavenger species richness per carcass and carcass consumption time and rate increased with carcass size, while carcass detection time and percentage of carrion biomass consumed were negatively related to carcass size. Strikingly, most of the carrion biomass was consumed by facultative scavengers, represented by large mammalian carnivores, rather than by obligate scavengers (i.e. vultures). Scavenging network nestedness tended to be higher at larger carcasses, and nestedness was sensitive to the removal of the most connected species in the network (spotted hyena) rather than vultures. When comparing scavenging and predation assemblages, crucial size‐dependent differences emerge. Also, we identified a traditionally ignored mechanism by which hunting large prey could be relatively less profitable for predators, namely the costs associated with competition from scavengers and decomposers.     

Trophic Facilitation or Limitation? Comparative Effects of Pumas and Black Bears on the Scavenger Community

Scavenging is a widespread behaviour and an important process influencing food webs and ecological communities. Large carnivores facilitate the movement of energy across trophic levels through the scavenging and decomposition of their killed prey, but competition with large carnivores is also likely to constrain acquisition of carrion by scavengers. We used an experimental approach based on motion-triggered video cameras at black-tailed deer (Odocoileus hemionus columbianus) carcasses to measure the comparative influences of two large carnivores in the facilitation and limitation of carrion acquisition by scavengers. We found that pumas (Puma concolor) and black bears (Ursus americanus) had different effects on their ecological communities. Pumas, as a top-level predator, facilitated the consumption of carrion by scavengers, despite significantly reducing their observed sum feeding times (165.7 min±21.2 SE at puma kills 264.3 min±30.1 SE at control carcasses). In contrast, black bears, as the dominant scavenger in the system, limited consumption of carrion by scavengers as evidenced by the observed reduction of scavenger species richness recorded at carcasses where they were present (mean = 2.33±0.28 SE), compared to where they were absent (mean = 3.28±0.23 SE). Black bears also had large negative effects on scavenger sum feeding times (88.5 min±19.8 SE at carcasses where bears were present, 372.3 min±50.0 SE at carcasses where bears were absent). In addition, we found that pumas and black bears both increased the nestedness (a higher level of order among species present) of the scavenger community. Our results suggest that scavengers have species-specific adaptions to exploit carrion despite large carnivores, and that large carnivores influence the structure and composition of scavenger communities. The interactions between large carnivores and scavengers should be considered in future studies of food webs and ecological communities.     

Donor-Control of Scavenging Food Webs at the Land-Ocean Interface

Food webs near the interface of adjacent ecosystems are potentially subsidised by the flux of organic matter across system boundaries. Such subsidies, including carrion of marine provenance, are predicted to be instrumental on open-coast sandy shores where in situ productivity is low and boundaries are long and highly permeable to imports from the sea. We tested the effect of carrion supply on the structure of consumer dynamics in a beach-dune system using broad-scale, repeated additions of carcasses at the strandline of an exposed beach in eastern Australia. Carrion inputs increased the abundance of large invertebrate scavengers (ghost crabs, Ocypode spp.), a numerical response most strongly expressed by the largest size-class in the population, and likely due to aggregative behaviour in the short term. Consumption of carrion at the beach-dune interface was rapid and efficient, driven overwhelmingly by facultative avian scavengers. This guild of vertebrate scavengers comprises several species of birds of prey (sea eagles, kites), crows and gulls, which reacted strongly to concentrations of fish carrion, creating hotspots of intense scavenging activity along the shoreline. Detection of carrion effects at several trophic levels suggests that feeding links arising from carcasses shape the architecture and dynamics of food webs at the land-ocean interface.     

Rewilding traditional grazing areas affects scavenger assemblages and carcass consumption patterns

The abandonment of traditional livestock farming systems in Mediterranean countries is triggering a large-scale habitat transformation, which, in general, consists of the replacement of open grazing areas by woodlands through non-managed regeneration. As a consequence, wild ungulates are occupying rapidly the empty niche left by domestic ungulates. Both types of ungulates represent the main trophic resource for large vertebrate scavengers. However, a comparison of how vertebrate scavengers consume ungulate carcasses in different habitats with different ungulate species composition is lacking. This knowledge is essential to forecast the possible consequences of the current farmland abandonment on scavenger species. Here, we compared the scavenging patterns of 24 wild and 24 domestic ungulate carcasses in a mountainous region of southern Spain monitored through camera trapping. Our results show that carcasses of domestic ungulates, which concentrate in large numbers in open pasturelands, were detected and consumed earlier than those of wild ungulate carcasses, which frequently occur in much lower densities at more heterogenous habitats such as shrublands and forest. Richness and abundance of scavengers were also higher at domestic ungulate carcasses in open habitats. Vultures, mainly griffons (Gyps fulvus), consumed most of the carcasses, although mammalian facultative scavengers, mainly wild boar (Sus scrofa) and red fox (Vulpes vulpes), also contributed importantly to the consumption of wild ungulate carcasses in areas with higher vegetation cover. Our findings evidence that the abandonment of traditional grazing may entail consequences for the scavenger community, which should be considered by ecologists and wildlife managers.     

Implications of shared predation for space use in two sympatric leporids

Spatial variation in habitat riskiness has a major influence on the predator–prey space race. However, the outcome of this race can be modulated if prey shares enemies with fellow prey (i.e., another prey species). Sharing of natural enemies may result in apparent competition, and its implications for prey space use remain poorly studied. Our objective was to test how prey species spend time among habitats that differ in riskiness, and how shared predation modulates the space use by prey species. We studied a one‐predator, two‐prey system in a coastal dune landscape in the Netherlands with the European hare (Lepus europaeus) and European rabbit (Oryctolagus cuniculus) as sympatric prey species and red fox (Vulpes vulpes) as their main predator. The fine‐scale space use by each species was quantified using camera traps. We quantified residence time as an index of space use. Hares and rabbits spent time differently among habitats that differ in riskiness. Space use by predators and habitat riskiness affected space use by hares more strongly than space use by rabbits. Residence time of hare was shorter in habitats in which the predator was efficient in searching or capturing prey species. However, hares spent more time in edge habitat when foxes were present, even though foxes are considered ambush predators. Shared predation affected the predator–prey space race for hares positively, and more strongly than the predator–prey space race for rabbits, which were not affected. Shared predation reversed the predator–prey space race between foxes and hares, whereas shared predation possibly also released a negative association and promoted a positive association between our two sympatric prey species. Habitat riskiness, species presence, and prey species’ escape mode and foraging mode (i.e., central‐place vs. noncentral‐place forager) affected the prey space race under shared predation.     

Effects of vulture exclusion on carrion consumption by facultative scavengers

Vultures provide an essential ecosystem service through removal of carrion, but globally, many populations are collapsing and several species are threatened with extinction. Widespread declines in vulture populations could increase the availability of carrion to other organisms, but the ways facultative scavengers might respond to this increase have not been thoroughly explored. We aimed to determine whether facultative scavengers increase carrion consumption in the absence of vulture competition and whether they are capable of functionally replacing vultures in the removal of carrion biomass from the landscape. We experimentally excluded 65 rabbit carcasses from vultures during daylight hours and placed an additional 65 carcasses that were accessible to vultures in forested habitat in South Carolina, USA during summer (June–August). We used motion‐activated cameras to compare carrion use by facultative scavenging species between the experimental and control carcasses. Scavenging by facultative scavengers did not increase in the absence of competition with vultures. We found no difference in scavenger presence between control carcasses and those from which vultures were excluded. Eighty percent of carcasses from which vultures were excluded were not scavenged by vertebrates, compared to 5% of carcasses that were accessible to vultures. At the end of the 7‐day trials, there was a 10.1‐fold increase in the number of experimental carcasses that were not fully scavenged compared to controls. Facultative scavengers did not functionally replace vultures during summer in our study. This finding may have been influenced by the time of the year in which the study took place, the duration of the trials, and the spacing of carcass sites. Our results suggest that under the warm and humid conditions of our study, facultative scavengers would not compensate for loss of vultures. Carcasses would persist longer in the environment and consumption of carrion would likely shift from vertebrates to decomposers. Such changes could have substantial implications for disease transmission, nutrient cycling, and ecosystem functioning.     

Apex predators and the facilitation of resource partitioning among mesopredators

Apex predators may influence carnivore communities through the suppression of competitively dominant mesopredators, however they also provide carrion subsidies that could influence foraging and competition among sympatric mesopredators when small prey is scarce. We assessed coyote Canis latrans and red fox Vulpes vulpes winter diet overlap and composition from scats collected in two study areas with 3‐fold difference in grey wolf Canis lupus density due to a wolf control program. We hypothesized that differences in diet composition would be driven by the use of carrion, and tested whether 1) apex predators facilitate resource overlap, or 2) apex predators facilitate resource partitioning. We estimated the available biomass of snowshoe hares and voles based on pellet density and vole capture rates in each study area. We used molecular analysis to confirm species identification of predator scats, and used microscopic evaluation of prey remains to analyze diet composition of 471 coyote and fox scats. Ungulate carrion, voles and snowshoe hares comprised 73% of coyote and fox diet, and differences in use of carrion and microtines accounted for nearly 60% of the dissimilarity in diet among these canids. Carrion was the top‐ranked item in the coyote diet in both study areas, whereas carrion use by red foxes declined 3‐fold in the study area with higher wolf and small prey abundance. Diet overlap tended to be lower and diet diversity tended to be higher where wolves were more abundant, though these trends were not statistically significant. Taken together, our findings indicate that carrion provisions could facilitate resource partitioning in mesocarnivore communities by alleviating exploitation competition for small mammals.     

Identification of vertebrate scavengers of small mammal carcasses in a forested landscape

We identified vertebrate scavengers of small mammal carcasses at the 780-km² Savannah River Site during the winter of 2000–2001. Rodent carcasses, differing in size and visual conspicuousness, were placed in upland pine forests and bottomland hardwood forests during six 2-week periods. Sixty-two of the 96 carcasses (65%) were removed by vertebrates. With the aid of remote photography, we identified 11 species of scavengers removing carcasses. RaccoonsProcyon lotor, gray foxesUrocyon cinereoargenteus, and feral pigsSus scrofa scavenged most frequently. The mean elapsed time for carcass removal was 5.6 days. The number of carcasses removed by vertebrates did not differ significantly with respect to carcass size, visual conspicuousness, or habitat type; however, air temperature was strongly correlated (positively) with carcass removal. Our study demonstrates that many mammal species are capable of utilizing small carrion items as a food resource, and suggests that scavenging may account for a higher proportion of the diet of some facultative scavengers than is now widely assumed.     

Carcass Type Affects Local Scavenger Guilds More than Habitat Connectivity

Scavengers and decomposers provide an important ecosystem service by removing carrion from the environment. Scavenging and decomposition are known to be temperature-dependent, but less is known about other factors that might affect carrion removal. We conducted an experiment in which we manipulated combinations of patch connectivity and carcass type, and measured responses by local scavenger guilds along with aspects of carcass depletion. We conducted twelve, 1-month trials in which five raccoon (Procyon lotor), Virginia opossum (Didelphis virginiana), and domestic rabbit (Oryctolagus spp.) carcasses (180 trials total) were monitored using remote cameras in 21 forest patches in north-central Indiana, USA. Of 143 trials with complete data, we identified fifteen species of vertebrate scavengers divided evenly among mammalian (N = 8) and avian species (N = 7). Fourteen carcasses (9.8%) were completely consumed by invertebrates, vertebrates exhibited scavenging behavior at 125 carcasses (87.4%), and four carcasses (2.8%) remained unexploited. Among vertebrates, mammals scavenged 106 carcasses, birds scavenged 88 carcasses, and mammals and birds scavenged 69 carcasses. Contrary to our expectations, carcass type affected the assemblage of local scavenger guilds more than patch connectivity. However, neither carcass type nor connectivity explained variation in temporal measures of carcass removal. Interestingly, increasing richness of local vertebrate scavenger guilds contributed moderately to rates of carrion removal (≈6% per species increase in richness). We conclude that scavenger-specific differences in carrion utilization exist among carcass types and that reliable delivery of carrion removal as an ecosystem service may depend on robust vertebrate and invertebrate communities acting synergistically.     

Temporal resource partitioning mediates vertebrate coexistence at carcasses: The role of competitive and facilitative interactions

Unravelling how biodiversity is maintained despite species competition for shared resources has been a central question in community ecology, and is gaining relevance amidst the current biodiversity crisis. Yet, we have still a poor understanding of the mechanisms that regulate species coexistence and shape the structure of assemblages in highly competitive environments such as carrion pulsed resources. Here, we study how large vertebrates coexist in scavenger assemblages by adapting their diel activity at large ungulate carcasses in NW Spain. We used camera traps to record vertebrate scavengers consuming 34 carcasses of livestock and hunted wild ungulates, which allowed us to assess also differences regarding carcass origin. To evaluate temporal resource partition among species, we estimated the overlap of diel activity patterns and the mean times of each scavenger at carcasses. We recorded 16 species of scavengers, 7 mammals and 9 birds, and found similar richness at both types of carcasses. Birds and mammals showed contrasting diel activity patterns, with birds using carcasses during daytime (mean= 11:38 h) and mammals mostly at night (23:09 h). The unimodal activity patterns of scavengers showed asynchronous peaks among species. Subordinate species modified their activity patterns at carcasses used by apex species to reduce temporal overlap. Also, diel activity patterns of vultures closely followed those of corvids, suggesting facilitation processes in which corvids would enhance carcass detection by vultures. Two mammal species (12.5%) increased nocturnality at carcasses of hunted ungulates, which could be a response to human disturbance. Our results suggest that both temporal segregation and coupling mediate the coexistence of large vertebrates at carcasses. These mechanisms might lead to richer scavenger assemblages and thereby more efficient ones in driving critical ecosystem functions related to carrion consumption, such as energy and nutrient recycling and biodiversity maintenance.     

Effect of scavenging on predation in a food web

Scavenging can have important consequences for food web dynamics, for example, it may support additional consumer species and affect predation on live prey. Still, few food web models include scavenging. We develop a dynamic model that includes two facultative scavenger species, which we refer to as the predator or scavenger species according to their natural scavenging propensity, as well as live prey, and a carrion pool to show ramifications of scavenging for predation in simple food webs. Our modeling suggests that the presence of scavengers can both increase and decrease predator kill rates and overall predation in model food webs and the impact varies (in magnitude and direction) with context. In particular, we explore the impact of the amount of dynamics (exploitative competition) allowed in the predator, scavenger, and prey populations as well as the direction and magnitude of interference competition between predators and scavengers. One fundamental prediction is that scavengers most likely increase predator kill rates, especially if there are exploitative feedback effects on the prey or carrion resources like is normally observed in natural systems. Scavengers only have minimal effects on predator kill rate when predator, scavenger, and prey abundances are kept constant by management. In such controlled systems, interference competition can greatly affect the interactions in contrast to more natural systems, with an increase in interference competition leading to a decrease in predator kill rate. Our study adds to studies that show that the presence of predators affects scavenger behavior, vital rates, and food web structure, by showing that scavengers impact predator kill rates through multiple mechanisms, and therefore indicating that scavenging and predation patterns are tightly intertwined. We provide a road map to the different theoretical outcomes and their support from different empirical studies on vertebrate guilds to provide guidance in wildlife management.     

Moose (<Emphasis Type="Italic">Alces alces</Emphasis>) hunters subsidize the scavenger community in Alaska

In many temperate ecosystems animal carcasses resultant from wildlife harvest can provide a high-quality food source for myriad facultative scavengers. We investigated scavenger use of human-provisioned ungulate carrion from a fall moose (Alces alces) hunt during 2010 and 2011 on the Gustavus Forelands, Alaska, USA. Using data from remote cameras, we (1) identified the scavenger species that used these resources and (2) evaluated their spatial and temporal responses to this seasonal resource event by indexing their activity patterns and relative order of arrival at carrion sites. We also quantified the length of time carrion persisted and estimated the amount of moose biomass provisioned to vertebrate scavengers by human hunters. Our results indicated that 11 vertebrate species (five birds and six mammals) scavenged moose carrion. We found that the common raven was the only species documented at all carrion sites and the most abundant species at moose carrion sites. As a species group, corvids [black-billed magpie (Pica hudsonia), common raven (Corvus corax); 0.1 ± 2.3 days] were the first to arrive at human-provisioned moose carrion sites, whereas ursids [brown bear (Ursus arctos), black bear (U. americanus); 1.3 ± 1.0 days] arrived after corvids but sooner than expected and canids [gray wolf (Canis lupus), coyote (C. latrans); 3.9 ± 3.0] arrived later than expected compared to our null model. On average, carrion persisted >20 days and hunters provided scavengers with a minimum of 2720 kg (82.7 kg/km²) and 1815 kg (64.8 kg/km²) of moose carrion during 2010 and 2011, respectively. Understanding how scavengers, particularly large carnivores, interact with human-provisioned moose carrion at the rural–wildland interface is essential for mitigating potential human–wildlife conflicts associated with humans subsidizing predators with a high-quality food resource.     

Variation in the feeding pattern of red foxes in relation to changes in anthropogenic resource availability in a rural habitat of western Poland

The feeding pattern of red foxes Vulpes vulpes, i.e., the composition of their diet and dietary responses to fluctuations in the abundance of common voles Microtus arvalis were compared in the periods before and after the limitation of anthropogenic food availability in a rural area in western Poland. During the winter seasons of 1996/97–2014/15, the diet of the foxes was estimated by analysing the stomach contents of individuals shot from November to March and the index of vole abundance was obtained by counting their burrow entrances. The major component of the fox diet over the entire study period was anthropogenic food (mainly, the remains of farm animals) that showed both the highest average proportion in the stomach content volume (53.4%) and the highest average frequency of occurrence in the stomachs (62.7%), whereas small mammals were the second important component (27.5% and 54.2%, respectively). The frequency of anthropogenic food decreased and the frequencies of wild ungulate carrion and other wild vertebrates (mainly birds) increased after the limitation of anthropogenic resources. The observed fluctuations in the index of vole abundance resulted in positive changes in the small mammal frequency and negative changes in the anthropogenic food frequency, but the course of these relationships did not significantly differ between the two periods. The frequency of hares in fox stomachs did not change significantly between these periods, but recently the occurrence of hares in the diet of foxes increased with vole abundance. This study indicated that the reduction of anthropogenic food availability for carnivorous mammals may result in their switching to other prey species and potentially may have a negative influence on the demography of such prey species.     

Habitat characteristics from local to landscape scales combine to shape vertebrate scavenging communities

Abiotic and biotic factors modulate carcass consumption by scavengers, affecting ecosystem functioning. Habitat structure is arguably a key factor influencing scavenging, but its role remains poorly understood, particularly at small spatial scales. We examine how habitat characteristics at landscape (50–1000 m radius) and local (≤10 m radius) scales around carrion affect the structure of vertebrate scavenging communities. We used remote cameras to monitor the consumption of 151 ungulate carcasses in one temperate (55 carcasses) and two Mediterranean (56 and 40 carcasses) study areas in Spain in 2011–2013. Our results showed complex habitat–scavenger relationships that mainly relied upon the spatial scale, the type of carcass and the study area. While the response of scavenger richness to habitat characteristics was consistent across study areas, the effects of diversity varied regionally at the landscape scale. Large and medium-sized carcasses in open landscapes had lower scavenger richness, likely because open habitats promote vulture dominance. At the local scale, shrub cover lowered scavenger richness and diversity, hindering carrion location by avian scavengers. Our results suggest that the structure of vertebrate scavenging assemblages at carcasses is driven by carcass and habitat characteristics operating as ecological filters at different scales (i.e. local, landscape, and biogeographical), which affect a species’ ability to locate, access and dominate carrion. Understanding the factors underlying the complex habitat–community relationships shown here has implications for managing key ecosystem functions and services. We propose a multi-scale conceptual framework to disentangle scavenger–carcass relationships.     

Long-term changes in the feeding pattern of red foxes Vulpes vulpes and their predation on brown hares Lepus europaeus in western Poland

The aim of this study was to estimate long-term changes in the winter feeding pattern of red foxes Vulpes vulpes and in their predation on brown hares Lepus europaeus in relation to the decreasing abundance of hares in western Poland in 1965/1966–2006/2007. The frequencies of occurrence in the stomachs of culled foxes (N?=?726) were used as indices of prey capture rates. The average autumn density of brown hares in the study area decreased from 48 individuals/km² at the turn of the 1960s and 1970s to seven individuals/km² in 1999–2006. Hares and small rodents were the main food classes of foxes in western Poland at the turn of the 1960s and 1970s; however, the occurrence of hares in the fox diet subsequently decreased, and they were replaced by livestock carrion. The relationship between the occurrence frequency of hares in the fox diet and the hare density was best described by sigmoid equation. It indicates that the red fox showed a type III functional response to long-term changes in hare abundance. When predation rate index was estimated on the basis of functional response, the potential fox predation was density-dependent at low to intermediate hare densities (<25 individuals/km²). This finding suggests that the increase in the number of low-density hare populations may require intensive management measures, e.g. simultaneous use of fox control and habitat improvement.     

The nested structure of a scavenger community

Scavenging is a widespread phenomenon in vertebrate communities which has rarely been accounted for, in spite of playing an essential role in food webs by enhancing nutrient recycling and community stability. Most studies on scavenger assemblages have often presented an oversimplified view of carrion foraging. Here, we applied for the first time the concept of nestedness to the study of a species-rich scavenger community in a forest ecosystem (Białowieża Primeval Forest, Poland) following a network approach. By analysing one of the most complete datasets existing up to now in a pristine environment, we have shown that the community of facultative scavengers is not randomly assembled but highly nested. A nested pattern means that species-poor carcasses support a subset of the scavenger assemblage occurring at progressively species-rich carcasses. This result contradicts the conventional view of facultative scavenging as random and opportunistic and supports recent findings in scavenging ecology. It also suggests that factors other than competition play a major role in determining community structure. Nested patterns in scavenger communities appear to be promoted by the high diversity in carrion resources and consumers, the differential predictability of the ungulate carcass types and stressful environmental conditions.     

Intra-guild competition and its implications for one of the biggest terrestrial predators, Tyrannosaurus rex

Identifying tradeoffs between hunting and scavenging in an ecological context is important for understanding predatory guilds. In the past century, the feeding strategy of one of the largest and best-known terrestrial carnivores, Tyrannosaurus rex, has been the subject of much debate: was it an active predator or an obligate scavenger? Here we look at the feasibility of an adult T. rex being an obligate scavenger in the environmental conditions of Late Cretaceous North America, given the size distributions of sympatric herbivorous dinosaurs and likely competition with more abundant small-bodied theropods. We predict that nearly 50 per cent of herbivores would have been within a 55–85 kg range, and calculate based on expected encounter rates that carcasses from these individuals would have been quickly consumed by smaller theropods. Larger carcasses would have been very rare and heavily competed for, making them an unreliable food source. The potential carcass search rates of smaller theropods are predicted to be 14–60 times that of an adult T. rex. Our results suggest that T. rex and other extremely large carnivorous dinosaurs would have been unable to compete as obligate scavengers and would have primarily hunted large vertebrate prey, similar to many large mammalian carnivores in modern-day ecosystems.     

Intraguild predation of lynxes on foxes: evidence of interference competition?

There is a growing focus among ecologists on the importance of predatory interactions between competing species, but because of its mixed character. it is difficult to pinpoint the possible, competitive component of the interaction. We tested degree of prey consumption in intraguild predation of Eurasian lynxes on red foxes against assumed 'pure' predation. i.e, roe deer and mountain hares. The proportion of uneaten fox carcasses was highly significantly larger than the proportion of both other prey species, indicating that interference competition may play a role in the intraguild predation of lynxes on red foxes.     

Resource use by an introduced and native carrion flies

The carrion fly Chrysomya rufifacies has recently been introduced to North America. Larvae of this species are facultative predators on other carrion larvae, and are known to reduce populations of the New World fly Cochliomyia macellaria in the laboratory and in certain field situations. In order to identify conditions under which native taxa might avoid interaction with the invader, we examined broad patterns of resource use by capturing postfeeding larvae as they left a carcass. The Calliphorinae were least similar to C. rufifacies since they were able to exploit smaller carrion, showed a peak in density during cold weather while C. rufifacies numbers were low, and occurred much earlier than the invader during succession within a carcass. Phormia regina also was most abundant during cold weather. The Sarcophagidae were able to exploit smaller carcasses than the invader but are likely to encounter it in larger carcasses. C. macellaria was the species most similar to C. rufifacies in carrion use, and probably is reduced in number by the invader wherever they coexist. In contrast to all other taxa, C. rufifacies exited a carcass alone, suggesting that other larvae of the same age were attacked. Manipulation of a conspicuous predator, the ant Solenopsis invicta, revealed a negative effect on numbers of P. regina and C. macellaria.