Cascading effects of insectivorous birds and bats in tropical coffee plantations

Abstract

The loss of apex predators is known to have reverberating consequences for ecosystems, but how changes in broader predator assemblages affect vital ecosystem functions and services is largely unknown. Predators and their prey form complex interaction networks, in which predators consume not only herbivores but also other predators. Resolving these interactions will be essential for predicting changes in many important ecosystem functions, such as the control of damaging crop pests. Here, we examine how birds, bats, and arthropods interact to determine herbivorous arthropod abundance and leaf damage in Costa Rican coffee plantations. In an exclosure experiment, we found that birds and bats reduced non-flying arthropod abundance by -35% and -25%, respectively. In contrast, birds and bats increased the abundance of flying arthropods, probably by consuming spiders. The frequency of this intraguild predation differed between birds and bats, with cascading consequences for coffee shrubs. Excluding birds caused a greater increase in herbivorous arthropod abundance than excluding bats, leading to increased coffee leaf damage. Excluding bats caused an increase in spiders and other predatory arthropods, increasing the ratio of predators to herbivores in the arthropod community. Bats, therefore, did not provide benefits to coffee plants. Leaf damage on coffee was low, and probably did not affect coffee yields. Bird-mediated control of herbivores, however, may aid coffee shrubs in the long-term by preventing pest outbreaks. Regardless, our results demonstrate how complex, cascading interactions between predators and herbivores may impact plants and people.

Bats initiate vital agroecological interactions in corn

“…Recent attempts to experimentally test the effectiveness of bats as pest suppressors have focused on tropical agroforestry (15)(16)(17), where bats glean insects from vegetation. No such study has been conducted in ubiquitous and cosmopolitan row crops such as corn, where bats hawk insects from the air.…”

Net neutral effects of a generalist vertebrate predator on seed production result from simultaneous suppression of plant antagonists and mutualists

“…Indeed, in the presence of frogs, proportional leaf damage caused by grasshoppers was less than 8%. Such low leaf damage may be offset by the compensative growth of plants (Karp & Daily 2014), and would not necessarily result in a significant reduction in seed output (Puentes & Ågren 2012). To this end, the frog effects on seed production could be trivial in the presence of grasshoppers.…”

“…Predators can modify community structure and ecosystem functioning by generating trophic cascading effects (Hairston, Smith, & Slobodkin 1960;Paine 2002;Schmitz 2008;Griffin et al 2011;Karp & Daily 2014) that operate through a wide variety of pathways (Pearson 2010). These different types of interactions are usually measured in separate studies, and often in separate ecosystems.…”

Complex Ecological Interactions in the Coffee Agroecosystem

“…It appears that intraguild predation may be implicated, and the increase of herbivores when birds are removed may, at least partially, result from a trophic cascade with five trophic levels (vertebrate predators, spiders, parasitic wasps, herbivores, and plants) (Figure 2). Another study in coffee plantations in Costa Rica suggests similar intraguild predation with bats but not with birds (Karp et al 2014).…”