Abstract
Predator-prey dynamics are fundamental in shaping and regulating wildlife communities; however, these relationships are often altered by urbanization. An urban predation paradox, where predation rates are lower in urban areas despite an increase in predator abundance, has been observed in some predator communities. We looked for evidence of an urban predation paradox in a raptor community in a large urban forest fragment in north Texas, USA. From May–August 2019, we conducted weekly raptor surveys and deployed prey mimics along an urban-to-rural gradient within the forest fragment. We examined relationships between predation rates on mimics, predator abundance, and urbanization intensity using a variety of statistical tests. We detected 161 raptors representing eight species and found that raptor activity was significantly higher in our low urbanization sites. Of the 732 prey mimics deployed, 61 were attacked, and we found no relationship between predation rates and urbanization. Furthermore, we found no relationship between raptor activity and depredation events. Although we failed to find evidence for an urban predation paradox, our results showed a decoupling of the relationship between the abundance of predators and prey in this urban setting. The use of prey mimics is a useful tool for assessing predator-prey dynamics, and more research is necessary to fully understand the impacts of urbanization on this important ecological process.
Highlights
Academic Editor: Salvidio SebastianoUrbanization is driving land-use change across the globe at an unprecedented rate [1].The conversion of historically natural habitats to developed areas alters the composition of wildlife communities within ecosystems as species sensitive to urbanization are replaced by those able to exploit this new environment [2]
The contradiction of predator proliferation and predation relaxation within urban areas is known as the urban predation paradox, which stands in opposition to the positively correlated relationship between predator abundance and predation rates in natural ecosystems [6]
We did not use data from the medium-urbanization sites for these reasons: (1) comparing only high and low sites allowed us to look at the largest difference in levels of urbanization; (2) by comparing only high and low sites, we decreased the likelihood of individual raptors being present at multiple sites; (3) the medium site had high variation in raptor activity, possibly driven by station-level factors that altered raptor detectability; and (4) the medium site contained an abundance of giant ragweed (Ambrosia trifida) that made it difficult to place models in locations where they could be seen by hunting raptors
Summary
The conversion of historically natural habitats to developed areas alters the composition of wildlife communities within ecosystems as species sensitive to urbanization are replaced by those able to exploit this new environment [2]. These changes disrupt predator-prey dynamics, a critical part of ecosystem function [3]. The first is predator proliferation, a frequently observed phenomenon in which predator densities are greater within urban areas than surrounding natural ones. The second is a reduction in predation rates in urban areas when compared to natural ones, known as predation relaxation [5]. The contradiction of predator proliferation and predation relaxation within urban areas is known as the urban predation paradox, which stands in opposition to the positively correlated relationship between predator abundance and predation rates in natural ecosystems [6]
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