Abstract
Despite increasing knowledge about the effects of habitat loss on pollinators in natural landscapes, information is very limited regarding the underlying mechanisms of forest fragmentation affecting plant-pollinator interactions in such landscapes. Here, we used a network approach to describe the effects of forest fragmentation on the patterns of interactions involving the understory dominant palm Astrocaryum mexicanum (Arecaceae) and its floral visitors (including both effective and non-effective pollinators) at the individual level in a Mexican tropical rainforest landscape. Specifically, we asked: (i) Does fragment size affect the structure of individual-based plant-pollinator networks? (ii) Does the core of highly interacting visitor species change along the fragmentation size gradient? (iii) Does forest fragment size influence the abundance of effective pollinators of A. mexicanum? We found that fragment size did not affect the topological structure of the individual-based palm-pollinator network. Furthermore, while the composition of peripheral non-effective pollinators changed depending on fragment size, effective core generalist species of pollinators remained stable. We also observed that both abundance and variance of effective pollinators of male and female flowers of A. mexicanum increased with forest fragment size. These findings indicate that the presence of effective pollinators in the core of all forest fragments could keep the network structure stable along the gradient of forest fragmentation. In addition, pollination of A. mexicanum could be more effective in larger fragments, since the greater abundance of pollinators in these fragments may increase the amount of pollen and diversity of pollen donors between flowers of individual plants. Given the prevalence of fragmentation in tropical ecosystems, our results indicate that the current patterns of land use will have consequences on the underlying mechanisms of pollination in remnant forests.
Highlights
Deforestation is the major cause of fragmentation and spatial isolation of populations in the tropics [1], with potential to increase species or population extinction rates [1,2]
We addressed the following questions: (i) Does fragment size affect the structure of individual-based plant-pollinator networks? (ii) Does the core of highly interacting visitor species change along the fragmentation size gradient? (iii) Does forest fragment size influence the abundance of effective pollinators of A. mexicanum?
Of the 60 floral visitor species collected, just one to eight species were present in the central core of highly generalist species: E. centralis (Coleoptera), M. mexicanus (Coleoptera), C. aberrans (Coleoptera), Mystrops sp. (Coleoptera), Unidentified sp1 (Diptera), Unidentified sp1 (Coleoptera), Unidentified sp2 (Coleoptera)
Summary
Deforestation is the major cause of fragmentation and spatial isolation of populations in the tropics [1], with potential to increase species or population extinction rates [1,2]. Despite the importance of ecological interactions in the structure and stability of biological communities over time and space [3], most studies have focused only on populations and species loss, but studies on the consequences of fragmentation on ecological processes are gaining prominence in the literature [4, 5, 6, 7]. Under a unified framework of species interactions, studies have focused on the structural properties of plant-pollinator networks at the community level in different systems and habitats throughout the Earth [16, 17, 18, 19], including the effects of habitat loss on these networks [20, 21, 22]. The topological structure of these ecological networks can be described through patterns of species interactions such as nestedness, modularity, specialization and diversity of interactions (reviewed by [23]). Despite the increase in knowledge on plant–pollinator networks at the community level, few studies have evaluated how these mutualistic relationships vary within biological populations, but see [24]
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