Negative Correlation between Ant and Spider Abundances in the Canopy of a Bornean Tropical Rain Forest

Abstract

In tropical rain forests, high canopy trees have diverse and abundant populations of ants and spiders. However, accessing high trees and their fauna remains difficult; thus, how ants and spiders interact in the canopy remains unclear. To better understand the interspecific interactions between these two dominant arthropod groups, we investigated their spatial distributions at the canopy surface in a tropical rain forest in Borneo. We sampled ants and spiders six times between 2009 and 2011 by sweeping with an insect net at the tree crown surfaces of 190 emergent or tall (≥20 m in height) trees. We collected 438 ant individuals belonging to 94 species and 1850 spider individuals (1630 juveniles and 220 adults) belonging to 142 morphospecies (adults only) from a total of 976 samples. The fact that we collected four times more spider individuals than ant individuals suggests that fewer ants forage at the tree crown surface than previously thought. The number of spider individuals negatively correlated with the number of ant individuals and the number of ant species, indicating significant exclusivity between ant and spider spatial distributions at the tree crown surface. Niche-overlap between the two taxa confirmed this observation. Although our data do not address the causes of these spatial distributions, antagonistic interspecific interactions such as interference behaviors and intra-guild predation are ecological mechanisms that give rise to exclusive spatial distributions.

The Influence of Tree Diversity on Natural Enemies—a Review of the “Enemies” Hypothesis in Forests

“…Nevertheless, even those ants preferably foraging for plantbased resources affect other arthropods and can reduce the densities of herbivores [59]. Likewise, ants may interfere with other predators, particularly spiders [39,60].…”

“…Individual predator taxa can respond differently to tree diversity, which may change predator community structure and interactions, but there is only limited data on intraguild interactions in forests. For example, the presence of ants can indirectly shift spider communities [60] from active hunters (more vulnerable to ants) to web builders (less vulnerable), with stronger changes in more diverse forests [39], giving some insight into how tree diversity may relate to intraguild interactions. In turn, different enemies can also be complementary, for example, when birds and ants as generalized predators have additive effects on caterpillar suppression as long as bird predation on ants is limited [40••].…”

Spatial covariance of herbivorous and predatory guilds of forest canopy arthropods along a latitudinal gradient

“…Similarly, inter‐guild competition can be observed in predators. For example spiders partly compete with ants for prey (Halaj et al ., 1997; Mestre et al ., 2012), and negative co‐occurrence of ants and spiders was observed in the canopies of a lowland rainforest (Katayama et al ., 2015). However, arboreal ants are well known to consume the sugar‐rich secretions of Hemiptera and plant extrafloral nectaries (Davidson, 1997; Davidson et al ., 2003), and can therefore be considered similar to primary consumers (herbivores).…”

Stable isotope analysis reveals the importance of plant‐based diets for tropical ant‐mimicking spiders

“…This suggests that the use of plant‐based diets in spiders may contribute to the greater abundance of spiders rather than ants in the canopy layers of tropical forests (Basset ; Katayama et al . ). Along with field observations of feeding behavior, food preference experiments and digestive enzyme assays, stable isotope techniques would help to better understand the diverse modes of ant mimicry and use of plant‐based diets in spiders.…”

“…The ant‐mimicking spiders may need to compete for food resources with the model ants, because ants and spiders are often assumed to be general predators and there are antagonistic interactions between the two arthropod groups (Sanders & Platner ; Katayama et al . ). Meanwhile, earlier studies have suggested that plant‐based diets, such as floral nectar, extrafloral nectar and honeydew produced by hemipterans, are an important nutrient source for many spider species, including ant‐mimicking spiders (Taylor & Foster ; Jackson et al .…”