Indirect effects of habitat fragmentation on seed dispersers influence plant community structure

A bird species eating fruits on islands of the Thousand Island Lake

Traditional studies generally consider habitat fragmentation as a driver of downsizing of plant seeds due to the disappearance of large seed dispersing vertebrates. However, most of these studies focuses on old‐growth forests, and much less is known about influences of habitat fragmentation on seed size pattern in patches of regenerating forests. This pattern may differ for secondary forest fragments where differential migration ability rather than persistence of seed dispersers may be driving plant community assembly.

To answer this question, we collected species distribution data of plants, birds, large and small mammals on islands in the Thousand Island Lake, China. We found that both richness and abundance of birds are determined by island size, but not for mammals. Such differential responses of potential seed dispersers led to a higher proportion of seed dispersal of bird-dispersed plants on large islands. Given that birds generally disperse smaller seeds than mammals, large islands may accumulate more small-seeded plants.

Structural equation model showing the main drivers of community level seed size patterns on islands in Thousand Island Lake

This is extremely useful to guide effective forest restoration given that many forests worldwide are empty forests without large mammals. Our study highlights the importance of keeping large continuous forests in order to retain mammals and their dispersal capabilities.

Link to paper

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