Long-term decline in prey increases predator competition

Bringing together data from a 50-year period to better-understand predator-prey interactions. Associate Editor, Matt Hayward discusses the recently published article, Changes in African large carnivore diets over the past half‐century reveal the loss of large prey by Creel et al.

Much of our understanding of ecology comes from systems that are assumed to represent the way life has interacted for millennia. Yet this assumption is becoming more and more questionable with advancements in our knowledge of the changes that have occurred since the demise of the megafauna in the Pleistocene and, more recently, the faunal loss of the Anthropocene.

Cheetah on rock Croc Bridge 94 - Matt Hayward
Image courtesy of Matt Hayward

Scott Creel’s team working in Kafue National Park, Zambia, were able to test how predator-prey interactions have changed over the past half century by comparing a large dataset of predation patterns collected by Mitchell and colleagues between 1960 and 1963, with their own data collected between 2013 and 2016.  This 50-year timeframe is very rare in ecology today, and hence provides unique insights into changes that have insidiously crept into this system with limited prior recognition. Kafue is a massive protected area – ostensibly on a scale sufficient to protect biodiversity – that has a large, intact predator community of lions, leopards, cheetah and African wild dogs, as well as a small population of spotted hyaenas.  Nonetheless, all these species are threatened with extinction and show continued declining populations globally. One major threat is a diminishing prey base, suggesting that the prey community is also declining.

Creel and colleagues found that large prey species (notably buffalo) are now relatively rare in the Kafue environment. This loss of prey base has caused the niche of each member of Kafue’s carnivore guild to compress, leading to an increased overlap of carnivore diets. All four large carnivores now concentrate their predation on four relatively small species: impala, puku, lechwe and warthog; and each of these species remains relatively abundant in Kafue.

These results have important implications for a suite of factors relevant to ecologists. Firstly, there is a need to acknowledgement that modern day ecosystems are suffering from a simplification associated with past faunal loss. Caution should be used in drawing broad conclusions to modern simplified ecological systems when the increased complexity of past systems may negate patterns we now see – the ghost of competition/predation past may still be present.

Secondly, monitoring programmes should include assessment of whether prey depletion alters patterns of predation or competition within predator guilds. This is important because these interactions affect the distribution and abundance of both predators and prey.

Thirdly, from a conservation viewpoint, species threatened by prey depletion would benefit predominately by mitigating the loss of key dietary components. In Kafue, targeted efforts to increase buffalo and other large herbivore abundance will serve to broaden the niches of the predator guild. Elsewhere, efforts to restore specific large predators’ preferred prey species seems important.

This study illustrates the importance of recognising historical studies and their value. By coupling these with robust analytical tools that can yield important insights into predator – prey interactions, we can improve our understanding of ecology.

Read the full article, Changes in African large carnivore diets over the past half‐century reveal the loss of large prey in Journal of Applied Ecology.

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