Crop damage of Eriotheca gracilipes (Bombacaceae) by the Blue-Fronted Amazon (Amazona aestiva, Psittacidae), in the Brazilian Cerrado.

J Ragusa-Netto

doi:10.1590/1519-6984.04713

Abstract

Seed predation has major effects on the reproductive success of individuals, spatial patterns of populations, genetic variability, interspecific interactions and ultimately in the diversity of tree communities. At a Brazilian savanna, I evaluated the proportional crop loss of Eriotheca gracilipes due the Blue-Fronted Amazon (Amazona aestiva) during a fruiting period. Also, I analyzed the relationship between proportional crop loss to Amazons and both fruit crop size and the distance from the nearest damaged conspecific. Trees produced from 1 to 109 fruits, so that Amazons foraged more often on trees bearing larger fruit crop size, while seldom visited less productive trees. Moreover, the relationship between fruit crop sizes and the number of depredated fruits was significant. However, when only damaged trees were assessed, I found a negative and significant relation between fruit crop size and proportional crop loss to Blue-Fronted Amazons. Taking into account this as a measure more directly related to the probability of seed survival, a negative density dependent effect emerged. Also, Amazons similarly damaged the fruit crops of either close or distant neighboring damaged trees. Hence, in spite of Blue-Fronted Amazons searched for E. gracilipes bearing large fruit crops, they were swamped due to the presence of more fruits than they could eat. Moderate seed predation by Blue-Fronted Amazons either at trees with large fruit crops or in areas where fruiting trees were aggregated implies in an enhanced probability of E. gracilipes seed survival and consequent regeneration success.

Highlights

Seed predation is one of the main processes limiting initial plant recruitment (Janzen, 1971; Wenny, 2000)
During the earliest stage of the plant life cycle this process has a direct effect on plant reproductive success and plays a significant role in determining the spatial structure and dynamics of plant populations (Janzen, 1971; Hulme, 1997; Nathan and Muller-Landau, 2000)
Seed predation may be either positively or negatively densitydependent and the pattern can be expected to vary with the relative abundance of seeds and their predators

Summary

Introduction

Seed predation is one of the main processes limiting initial plant recruitment (Janzen, 1971; Wenny, 2000). Plentiful seed availability might swamp seed predators and a negative density-dependent response may occur (Janzen, 1970; Manson et al, 1998). In this respect, a canopy or a collection of neighboring canopies bearing enhanced fruit crop sizes tend to cause predator satiation, which consequence is an improved seed survival within a dense seed patch (Augspurger, 1981; Ghazoul and Satake, 2009). Seed success is strongly influenced by pre-dispersal seed predators, and negative density-dependent effect on seed predation or predator satiation will determine the fecundity level of individual plants (Forget et al 2000; Ghazoul and Satake, 2009)

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Conclusion