The effect of plant dispersal on ecosystem function

Date of Award

May 2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Advisor(s)

Jason D. Fridley

Keywords

ecosystems, functional traits, island biogeography, islands, plant dispersal, plant ecology

Subject Categories

Life Sciences

Abstract

One of the central aims of ecology is to understand how biotic processes drive ecosystem functions such as carbon storage and nutrient cycling. The goal of this dissertation is to test whether plant dispersal can drive ecosystem function by studying how dispersal limitation drives functional trait variation and community succession across three different study systems. First, I tested the role of spatial isolation and associated dispersal limitation on functional variation in the plant communities on 30 uninhabited islands in the Gulf of Maine. I found that spatial isolation was a significant driver of functional trait variation on these islands even after accounting for key environmental covariates. Second, I conducted a controlled experiment to directly test the role of dispersal limitation on the colonization and establishment of old-field species in New York State. The scope of this study was to test between direct (immigrant selection hypothesis) and neutral (species pool hypothesis) mechanisms by which dispersal limitation could drive functional trait variation. Dispersal limitation was a key driver of functional variation in this system, with most variation attributed to species pool effects. I also found some support for the immigrant selection hypothesis for one trait (specific leaf area), suggesting that dispersal filters can directly select for shifts in functional composition. Overall effects of dispersal limitation on functional composition declined from the colonization to the establishment phase, however, suggesting the increasing importance of environmental and biotic filters on functional variation. The final project of this dissertation involved surveying the plant communities, functional traits, and ecosystem properties of 20 islands in Clarks Hill Lake reservoir, Georgia. Twelve of these islands were logged at the time of lake formation in 1954, and the first scope of this project was to test whether dispersal limitation had long-term effects on successional dynamics in this system. I found that island isolation had substantial effects on the relative abundance of dominant tree species on these islands, considerably reducing the abundance of one dominant tree species in particular (Pinus taeda), and this effect was only evident on previously logged islands. This finding supports the role of dispersal limitation as a significant driver of long-term successional dynamics. The second scope of this project was to evaluate the role of dispersal limitation as a driver of community functional trait variation and subsequent ecosystem function. I found that community-abundance-weighted variation of several key functional traits significantly varied with island isolation while controlling for edaphic and spatial covariates. Ecosystem properties such as soil organic matter quality and potential nitrogen mineralization similarly varied with island isolation, suggesting that dispersal limitation can have long-term legacy effects on ecosystem function. Altogether, the results of these projects provide strong evidence for the importance of plant dispersal as a key driver of ecosystem function and highlights several mechanisms by which dispersal limitation can lead to these effects.

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