![]() In two-link trophic systems only comprising plants and herbivores, the EEH predicts that the biomass of herbivores will increase with ecosystem productivity (Oksanen and Oksanen 2000). According to the EEH, variation in ecosystem productivity will cause the biomasses of each trophic group to shift to alternative equilibria in order to balance biomass exchange between them (Choquenot and Forsyth 2013). The exploitation ecosystems hypothesis (EEH) was initially invoked to explain spatial patterns in the biomasses of trophic groups (plants, herbivores and carnivores) (Rosenzweig 1971 Oksanen and others 1981). Thus, limited availability of prey may result in bottom-up limitation when population growth is more constrained by resources than by top-down control (Letnic and Dickman 2010). Variation of apex predators’ effects on mesopredators may occur because all animals require nutrients and energy. However, apex predators’ effects on mesopredators do not operate in isolation but interact in complex ways with other factors such as human activities, the composition of predator and prey assemblages and the productivity of ecosystems (Greenville and others 2014 Newsome and Ripple 2015 Swanson and others 2014). The removal of top predators and the concomitant relaxation of suppressive top-down effects can result in a dramatic increase in abundance of smaller predators, a trophic pathway described by the mesopredator release hypothesis (MRH) (Crooks and Soulé 1999 Newsome and others 2017). Such effects can occur due to top predators directly killing smaller predators (Helldin and others 2006 Merkle and others 2009) or as a result of competitive effects that can arise if smaller predators’ ability to obtain food resources is curtailed in the presence of larger predators (Schmitz and others 2004 Swanson and others 2014 Leo and others 2015). One key pathway via which apex predators can structure ecosystems is through their suppressive effects on populations of smaller predators (Prugh and others 2009 Ritchie and Johnson 2009). ![]() Consequently, restoring and maintaining the ecosystem services that top predators provide is a critical global imperative (Estes and others 2011 Ripple and others 2014). Disruption to ecosystems caused by the removal of apex predators, such as wolves, dingoes and sharks, has been identified as a major factor contributing to the loss of biodiversity in aquatic and terrestrial systems throughout the world (Estes and others 2011 Ripple and others 2014). Apex predators’ suppressive, top-down, effects on the populations and phenotypes of prey and smaller predators can have cascading effects on species at lower levels in food webs and result in changes to processes that affect the flow of energy and materials through ecosystems (Ripple and others 2014 Morris and Letnic 2017 Rees and others 2017). Our study provides evidence that top-down control exerted by apex predators can decouple population dynamics between mesopredators and their prey and thus have primacy over bottom-up effects.Īpex predators can play a pivotal role in maintaining healthy, balanced ecosystems (Estes and others 2011). Cat remains were present in 1% of dingo scats, and dietary overlap between cats and dingoes was high (0.75–0.82). Cat abundance was correlated positively with prey abundance where dingoes were rare but was not correlated with prey abundance where dingoes were common. Overall, cats were more abundant where dingoes were rare. We examined dingo and cat scats to provide mechanistic support for the idea that dingoes control cats through killing and exploitative competition. ![]() Using field data collected across the Dingo Fence, we test the predictions generated by MRH and EEH that cat populations should be bottom-up controlled by prey abundance (a proxy for primary productivity) where top-down control exerted by dingoes was weak but not where it was strong. Here, we take advantage of the manipulation of dingo abundance across Australia’s Dingo Fence to explore the primacy of top-down and bottom-up effects as drivers of feral cat abundance. The exploitation ecosystems hypothesis (EEH) predicts that biomass of apex predators will scale with primary productivity but herbivore and mesopredator biomass will remain constant due to top-down control. However, apex predators’ effects on mesopredators are also likely to be modulated by interactions with human activities and ecosystem productivity. The mesopredator release hypothesis (MRH) predicts that the removal of apex predators should lead to increased abundance of smaller predators through relaxation of suppressive, top-down effects.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |