Identifying mesopredator release in multi‐predator systems: a review of evidence from North America

Abstract

1. The mesopredator release hypothesis, defined as the change in distribution, abundance or behaviour of a middle-ranking predator in response to a decrease in density or distribution of an apex predator, is an increasingly popular topic in ecology. Terrestrial mesopredators have been reported as being released in multiple systems globally, particularly in North America, over the past century. 2. We reviewed 2687 scientific articles, of which we determined that 38 met our criteria for investigating mesopredator release (MR) in terrestrial North American mammalian predators. 3. We observed no support or mixed support for MR in 46% of all relevant studies, including conflicting evidence between measures (mesopredator distribution, abundance or behaviour) within a given study and among studies of the same community in different settings. 4. To advance the study of MR, we provide a conceptual framework that 1) highlights the multiple spatial, temporal and ecological scales at which mesopredator responses can occur; 2) suggests the relative weight of evidence for MR that is provided by measures of mesopredator responses at each scale; and 3) clearly defines the threshold for determining when MR is occurring. 5. In increasingly reshuffled predator communities with declining apex predators, there is a need for future studies to assess in more detail the contexts in which mesopredator behavioural responses scale up to the population-level processes and species-level distribution changes needed to identify these responses as MR.

Dhole pack size variation: Assessing effect of Prey availability and Apex predator

“…Statistically significant but moderate effect size reflects that the patterns were diffused at global scale. Patterns of subordinate predator response to apex predators numbers do not always mirror each other over temporal and spatial scales (Jachowski et al, 2020), pertaining to area specific ecological settings, anthropogenic disturbances, level of protection at reserve level and connectivity in the landscape at regional scale (Greenville, Wardle, Tamayo, & Dickman, 2014;Newsome, & Ripple, 2015). We did not find support for our third hypothesis, dhole pack size was not associated with high terrain ruggedness however, a low pack size has been reported from studies of high altitude and rugged terrain (Bashir, Bhattacharya, Poudyal, Roy, & Sathyakumar, 2014;Lyngdoh, Gopi, Selvan, & Habib, 2014).…”

Modelling the distribution and intraguild associations of an understudied mesocarnivore across the contiguous United States

“…At the same time, grey foxes are often found to benefit from apex carnivores, such as pumas and grey wolves, that limit coyote abundance or distribution and release grey foxes from competition (Levi & Wilmers, 2012; Newsome & Ripple, 2015). These equivocal findings are representative of a broader knowledge gap in carnivore community dynamics, namely, the relative influence of negative species interactions versus that of humans and habitat (Jachowski et al, 2020; Linnell & Strand, 2000; Moll et al, 2018).…”

Terrestrial mesopredators did not increase after top-predator removal in a large-scale experimental test of mesopredator release theory

“…These results from Australia add to the growing body of evidence from other countries that mesopredator suppression or release processes are not ubiquitous. Work from Europe 117 , 118 , Africa 119 – 123 , Asia 124 – 126 , North America 9 , 127 , and South America 128 , 129 also continue to report an absence of strong top-predator effects on mesopredators, with bottom-up effects appearing to be more strongly associated with mesopredator population changes. Yellowstone National Park in North America appears to be the location where these effects are most apparent, for wolves, with limited evidence for these processes available for almost all other large carnivores ( 2 ; see also 12 ).…”

“…Because many predators fulfil important ecological functions, such as regulation of herbivory 3 , 4 , the loss or removal of top-predator populations can be particularly concerning for some ecosystems 5 , 6 . One major concern is the potential for subsequent increases in the abundance and impacts of mesopredators that are reported to have devastating consumptive and non-consumptive effects on multiple species 7 – 9 , especially endangered prey species 10 . Mesopredators are expected to be suppressed by larger-sized top-predators, so losing or removing top-predators is expected to produce a ‘mesopredator release’ with undesirable cascading effects on prey fauna at lower trophic levels.…”