Cascading Effects of Birds and Bats in a Shaded Coffee Agroforestry System

Lauren Schmitt,Ivette Perfecto,Russell Greenberg,Peter Bichier,Guillermo Ibarra-Núñez,Caleb E Gordon

doi:10.3389/fsufs.2021.512998

Abstract

Volant vertebrate insectivores, including birds and bats, can be important regulators of herbivores in forests and agro-ecosystems. Their effects can be realized directly through predation and indirectly via intraguild predation. This paper examines data from bird and bat exclosures in coffee farms in Chiapas, Mexico in order to determine their effect on herbivores. Arthropods were sampled in 32 exclosures (with 10 coffee plants in each) and their paired controls three times during 6 months. After 3 months, herbivore and spider abundance increased, underscoring the importance of both intertrophic predation between volant vertebrate insectivores and herbivores and intraguild predation between volant vertebrate insectivores and spiders. After 6 months, herbivore abundance increased in the exclosures, which is indicative of a direct negative effect of birds and bats on herbivores. We suggest that intraguild predation is important in this food web and that seasonality may change the relative importance of intraguild vs. intertrophic predation. Results suggest a dissipating trophic cascade and echo the growing body of evidence that finds birds and bats are regulators of herbivores in agro-ecosystems.

Highlights

Defining trophic levels and outlining the connections between them has long been a fundamental goal in ecology
Our results highlight the role of intraguild predation in food webs with Volant vertebrate insectivores (VVIs), as well as the direct role of VVIs in consuming herbivores
Our findings support recent studies that indicate that VVIs can contribute to biocontrol, limiting arthropod populations in forests and agroecosystems (Greenberg et al, 2000; Kalka et al, 2008; Van Bael et al, 2008; WilliamsGuillén et al, 2008; Johnson et al, 2010; Böhm et al, 2011; Morrison and Lindell, 2012; Karp and Daily, 2014; Gras et al, 2016; Maas et al, 2016)

Summary

Introduction

Defining trophic levels and outlining the connections between them has long been a fundamental goal in ecology. Inter-trophic consumption (i.e., feeding between trophic levels, as when a predator eats an herbivore) is undoubtedly important in structuring food webs, but is complicated by intraguild predation. Intraguild predation (i.e., organisms in the same trophic level consuming one another) is very common (Gagnon et al, 2011). The feeding bias of predators—that is, whether they are primarily predating within or outside of their guild or trophic level—can have important consequences on food web structure. The relative importance of inter-trophic vs intra-guild predation has particular practical significance in managed ecosystems (Montoya et al, 2003). Natural enemies in the food web represent one of many tools for holistic pest management.

Methods

Results

Conclusion