Spiders as plant partners: Complementing ant services to plants with extrafloral nectaries

Abstract

In terrestrial communities, multitrophic interactions comprise a minimum of three trophic levels that interact among each other: plants, herbivores and their natural enemies. The top-down forces exerted by invertebrate predators on herbivores, and their cascading effect on plants, are very important to community structuring. Among major invertebrate predators, ants exert a strong impact on the density and spatial distribution of leaf and floral herbivores, which is reflected in the reproductive capacity of the plants. This important effect has only recently also been attributed to spiders. Studies of trophic interactions involving spiders and their impacts on the vegetation have increased considerably in the last few years. This is to be expected, considering that spiders are present in almost all terrestrial environments and occur in higher abundance in vegetation-rich areas. Regarded as excellent predators, spiders also use plants as foraging substrates, exploring differences in the plant architecture and in prey-capture strategies. Furthermore, spiders commonly prey on insect herbivores, which can result in a great decrease in herbivory rates, benefiting the host plants. In this chapter we will explore the hypothesis that spiders increase the reproductive value of plants with extrafloral nectaries, complementing the services provided by ants.