Graduate Thesis Or Dissertation
 

Effects of Aquatic Resource Subsidies on the Ecology of Terrestrial Top Predators

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  • Energetic resources transferred between distinct habitats or ecosystems, referred to as allochthonous resources, can greatly subsidize consumers in the recipient habitat, and thus influence food web structure and dynamics. Such subsidies may allow the growth of the consumer population to be decoupled from in situ productivity with effects on consumer abundance and behavior as well as on resident prey populations. Questions remain about the prevalence and intra-population variation of allochthonous resource use in apex predators. However, studying large carnivores is logistically difficult, time-consuming, and expensive because they are highly mobile, elusive and favor large areas with low human population densities. Under these circumstances, monitoring efforts using direct observation or invasive methods involving capture and handling are particularly challenging, may pose ethical concerns and often result in small sample sizes. As an alternative, noninvasive genetic sampling has many advantages but has traditionally been limited by high costs, low success rates, and high error rates largely due to the low quantity and quality of target DNA that is intrinsic to noninvasive samples. For this dissertation, I explored how abundant allochthonous subsidies affect apex carnivore foraging behavior, social ecology, and abundance. In Chapter 2, I outlined a detailed protocol for cost-effective and accurate noninvasive genotyping using single-nucleotide polymorphisms (SNPs) and multiplexed amplicon sequencing optimized for degraded DNA. The genotyping success rate for scat samples was 93%, and 100% for hair and tissue, representing a substantial increase compared to previous microsatellite- based studies while remaining at a low cost of under $5 per PCR replicate. I applied this method in Chapter 3 where I explored how wolf foraging ecology and demography are affected by the presence of recovered sea otter populations in areas with and without traditional ungulate prey. Wolves persisted after 6 years on a nearly complete marine diet, despite harvest occurring almost annually and without known supplemental immigration, by maintaining high fecundity. Our findings suggest that the recolonization of sea otters can allow wolves to persist on predominantly non-ungulate marine derived resources. In Chapter 4, I used camera traps, telemetry data, and scats to document the first predominantly piscivorous large felid population and the effects these aquatic subsidies may have on the density and social ecology of jaguars in Northern Pantanal, Brazil. In contrast to a diet dominated by terrestrial mammals elsewhere, the jaguar population we describe is the first to feed extensively on fish and to minimally consume mammals. These aquatic subsidies supported the highest jaguar population density estimate to date derived from camera traps and GPS collars. Contrary to their mostly solitary behavior elsewhere, we also documented social interactions previously unobserved between same-sex adults including cooperative fishing, co-traveling, and play. Collectively, this dissertation demonstrates that aquatic subsidies can alter the population size, social behavior and feeding ecology of apex carnivores. These unexpected results reveal that carnivores may be more flexible in their dietary requirements than previously believed, and challenge the notion that gray wolves and jaguars, two well-studied apex carnivores, depend on terrestrial mammalian prey for their persistence.
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  • Ongoing Research
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  • 2022-06-07 to 2023-07-08

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