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Apex consumers are declining worldwide. While the effects of apex predator declines on ecosystems are widely documented, the cascading effects of apex scavenger declines are poorly understood. We evaluated whether disease‐induced declines of an apex scavenger, the Tasmanian devil (Sarcophilus harrisii), increased carrion use by invertebrate scavengers. We manipulated devil access to 36 carcasses across a gradient of devil density from east to west Tasmania and measured carcass use by invertebrates. We found the amount of carcass removed within 5 days was 3.58 times lower at sites with the lowest devil densities. Adult carrion beetle (Ptomaphila lacrymosa) and blow fly (Calliphoridae) larvae abundances were two times higher at open‐access carcasses at low‐density sites than at intermediate‐ and high‐density sites. Adult beetles persisted for 10 days at the low‐density site but declined after 5 days when devils had access to carcasses in intermediate‐ and high‐density sites. Blow fly larvae abundance was not affected by devils in the low‐density site but decreased with devil access in intermediate‐ and high‐density sites. Our results suggest that apex scavenger declines may increase invertebrate scavenger abundance and their contribution to carrion decomposition, with potential cascading effects on nutrient cycling and ecosystems.
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Density‐dependent within‐patch movement behavior of two competing species
Abstract Movement behavior is central to understanding species distributions, population dynamics and coexistence with other species. Although the relationship between conspecific density and emigration has been well studied, little attention has been paid to how interspecific competitor density affects another species' movement behavior. We conducted releases of two species of competingTriboliumflour beetles at different densities, alone and together in homogeneous microcosms, and tested whether their recaptures‐with‐distance were well described by a random‐diffusion model. We also determined whether mean displacement distances varied with the release density of conspecific and heterospecific beetles. A diffusion model provided a good fit to the redistribution ofT. castaneumandT. confusumat all release densities, explaining an average of >60% of the variation in recaptures. For both species, mean displacement (directly proportional to the diffusion rate) exhibited a humped‐shaped relationship with conspecific density. Finally, we found that both species of beetle impacted the within‐patch movement rates of the other species, but the effect depended on density. ForT. castaneumin the highest density treatment, the addition of equal numbers ofT. castaneumorT. confusumhad the same effect, with mean displacements reduced by approximately one half. The same result occurred forT. confusumreleased at an intermediate density. In both cases, it was total beetle abundance, not species identity that mattered to mean displacement. We suggest that displacement or diffusion rates that exhibit a nonlinear relationship with density or depend on the presence or abundance of interacting species should be considered when attempting to predict the spatial spread of populations or scaling up to heterogeneous landscapes.
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- PAR ID:
- 10477790
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Ecology and Evolution
- Volume:
- 13
- Issue:
- 11
- ISSN:
- 2045-7758
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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