Toward a more robust link between theory and data in large mammal predator-prey ecology

Background/Question/Methods

There is a rich body of theory exploring predator-prey interactions, especially in relation to the role of predators on prey population dynamics. Likewise, many field studies have examined predator-prey interactions in the context of prey population growth or decline under predation mortality. However, the link between predator-prey theory and field data has not always been well articulated, especially in large mammal systems, which have high complexity and often are plagued by small sample size and low precision. Through literature review and simulations, we identify major gaps between theory and data in large mammal predator-prey research, and provide recommendations for strengthening this link through, for example, careful study design, refined models, and better parameter estimates.

Results/Conclusions

Theory supports the primacy of the predator functional response on prey population dynamics, but data testing the form of the response usually provide high uncertainty in the fitted models. This challenge is compounded because most predators rely on a variety of prey types, but multi-prey functional responses are difficult to parameterize and fit. Whether predator functional responses are prey dependent or predator:prey ratio dependent remains a source of much dissent but can fundamentally affect model outcomes; without sound theory, empiricists will continue to use whichever model explains most variation rather than selecting a model based on the biology of the system. Importantly, the predator numerical response also is poorly described, largely because of challenges in estimating predator populations across a range of densities and gaps in our understanding of the outcome of competition between predators. It follows that error in both the functional and numerical response is compounded when determining predation impacts on prey populations. Field studies assessing predator regulation would be well served by abandoning a largely predator-centric approach and instead determining whether the proportion of prey killed is density-dependent across a range of critical prey densities. In large mammal research there also remains the thorny issue of whether predator-prey systems are governed by alternative stable states and if predator control can release prey from low-density equilibria; ongoing work will not resolve this quandary because of confounds like the influence of alternate prey, predator-predator interactions, human harvest, and compensatory predation rates, on system stability. Notwithstanding these challenges, new telemetry technology opens a variety of opportunities to better link predator-prey data to theory, for example, by elucidating the role of cause-specific predation risk, interference competition, and spatial heterogeneity and scale, on trophic interactions and population trajectories.