Predator types, urbanization, and tree cover drive top-down control of herbivorous and carnivorous preys in an urban agroecosystem

Abstract

Prey-predator interactions hold significant importance, widely acknowledged as crucial processes within ecosystems. Yet, there is a scarcity of empirical data that effectively illustrates the influence of urbanization on such interactions. We performed a common garden experiment utilizing 1250 clay models to assess the predation risks faced by herbivorous and carnivorous prey in an urban agroecosystem in the southern Philippines. Our findings revealed significant differences in attack risks between the trophic levels, with herbivorous caterpillars (n = 246; 53.25%) experiencing higher predation rates compared to carnivorous lizards (n = 216; 46.75%). Interestingly, while the trophic level of the prey did not directly predict predation risk, the presence of predators showed significant effects. Arthropods emerged as the dominant predators of herbivorous prey compared to other predators, whereas mammalian predators predominantly attacked carnivorous prey. The landscape variable also had a strong influence on the risk of predation. We found that increasing tree cover was significantly related to increased predation risk, while built-up showed the opposite. Our research findings support the 'increasing disturbance hypothesis', suggesting that rising urbanization rates reduce predator diversity, resulting in a decrease and loss of predation pressure.

Predation risk of caterpillar preys in urban agroecosystem is shaped by arthropods and local landscape but not leaf herbivory: a common garden experiment

“…Previous studies have shown that caterpillar predation is positively linked to the landscape structure surrounding agricultural elds, such as higher forest cover and proximity to the forest interior, regardless of the identity of the natural enemy (Hohlenwerger et al 2022). Our observed predation pattern is similar to the previous ndings of Lidasan et al (2023) showing that arthropods were more dominant predators than others in the same system. Arthropod herbivores are common and abundant in tropical ecosystems and even in more disturbed urban agroecosystems, as they rely on limited plants for food and shelter in vegetation patches.…”

“…The attack frequency (1 = attacked, 0 = not attacked) was used as a binary response variable (dependent variable). Meanwhile, land-use cover proportions, DBH, and canopy openness were set as explanatory variables (see Lidasan et al (2023) for landscape analyses). We only included sites with heterogeneous land use cover in the nal GLM analysis and selected the best model based on the lowest values of the corrected Akaike's Information Criterion (AICc) and Akaike weights (wAICc) (Burnham and Anderson 2004).…”

“…Herbivory can also in uence the distribution of prey-predator interactions as foraging predators can identify their herbivorous prey using both volatile cues emitted when leaves are damaged and visual cues (i.e., increase the exposure); these cues increase the visibility and detectability of prey, making them more vulnerable to predation (Agrawal 1998;Reddy 2002;Fagundes et al 2017). However, other factors drive herbivory and prey-predator interactions, such as local and landscape structure and predator type (Lidasan et al 2023). The impact of land-use changes on prey-predator relationships is complex and context-dependent.…”

“…However, previous investigations assessing the impact of tree cover or vegetation proportions on both predator abundance and species richness have yielded varied and inconclusive outcomes (Lemessa et al 2015;Yang et al 2018). Most importantly and agreed by many studies, habitat loss, fragmentation, and degradation can all make prey more vulnerable to predation, while changes in prey or predator abundance can also affect the balance of power in these relationships (Belgrad and Griffen 2016;Ostandie et al 2021;Lidasan et al 2023).…”