Trophic Cascades in a Multicausal World: Isle Royale and Yellowstone

Abstract

Questions of whether trophic cascades occur in Isle Royale National Park (IRNP) or Yellowstone National Park's northern range (NR) cannot lead to simple, precise, or definitive answers. Such answers are limited especially by multicausality in the NR and by complex temporal variation in IRNP. Spatial heterogeneity, contingency, and nonequilibrium dynamics also work against simple answers in IRNP and NR. The existence of a trophic cascade in IRNP and NR also depends greatly on how it is defined. For example, some conceive of trophic cascades as entailing essentially any indirect effect of predation. This may be fine, but the primary intellectual value of such a conception may be to assess an important view in community ecology that most species are connected to most other species in a food web through a network of complicated, albeit weak, indirect effects. These circumstances that work against simple answers likely apply to many ecosystems. Despite the challenges of assessing the existence of trophic cascades in IRNP and NR, such assessments result in considerable insights about a more fundamental question: What causes population abundance to fluctuate? 325 Annu. Rev. Ecol. Evol. Syst. 2014.45:325-345. Downloaded from www.annualreviews.org Access provided by University of New Orleans on 12/08/14. For personal use only.

Can we save large carnivores without losing large carnivore science?

“…That wolves may not have been the cause of all the observed ecological changes in Yellowstone since the mid-1990s is argued by Kauffman et al (2010), Mech (2012) and others (e.g. Creel and Christianson, 2009;Winnie, 2012;Marshall et al, 2013;Marshall et al, 2014;Middleton, 2014;Peterson et al, 2014;see Table 2). The long term study of wolf-moose (Alces americanus)-habitat-climate relationships on Isle Royale illustrate the difficulties of attributing cause and effect even in very simple ecosystems (Vucetich and Peterson, 2004).…”

“…Carnivores are just one of many potential causal agents operating in ecosystems (Vucetich et al, 2005;Middleton, 2014;Peterson et al, 2014;Ford and Goheen, 2015). Yet for many studies claiming support for the MRH, TCH and BMTCH, the study framework is designed to create evidence for these hypotheses rather than being designed so that evidence for plausible alternative hypotheses is both tested and compared at the same time (Winnie, 2014).…”

“…This is because the direct and indirect effects of humans on all trophic levels may simply overshadow any carnivore effects (Muhly et al, 2013;Darimont et al, 2015;Clinchy et al, 2016;Kuijper et al, 2017). Carnivores are but one potential causal factor in a multicausal world (Vucetich and Peterson, 2004;Peterson et al, 2014;MacNulty et al, 2016;Engeman et al, 2017), and restoring large carnivores into these human-modified systems without removing the many other, more important causal factors influencing biodiversity loss is unlikely to succeed in reversing the situation . This is not to say that carnivore restoration efforts are unnecessary or should be avoided , but that we should more carefully consider the anticipated benefits of these actions against the biophysical and anthropogenic factors that mediate the top-down effects of carnivores.…”

Where can wolves live and how can we live with them?

“…https://www.youtube.com/results?search_query=wolves+change +rivers, viewed more than 35 million times, the degree, extent, and importance of such wolf-caused trophic cascades have been challenged (Mech, 2012;Allen et al, 2017) and are unclear (Peterson et al, 2014;Smith et al, 2016).…”

Environmental effects are stronger than human effects on mammalian predator-prey relationships in arid Australian ecosystems

“…Dickman et al, 1999;Letnic and Dickman, 2006). However, there remains a dearth of studies demonstrating these expected functional relationships for many threatened fauna persisting in desert ecosystems, and identifying the strongest factors influencing prey populations has proved difficult (Holmes, 1995;Marshall et al, 2014;Peterson et al, 2014). All components of food webs interact to some extent (Allen et al, 2017), but few interactions are strong enough to shape them.…”