How ecosystem functioning in tropical forests varies with anthropogenic land use and environmental change
File(s)
Author(s)
Harrison, Michelle
Type
Thesis
Abstract
The combined effect of habitat degradation and shifts in climate are pushing many
species towards local and global extinctions. Often, the most sensitive species to
disturbance are the most important for the maintenance of healthy ecosystems. With
conservation efforts focussing on biodiversity, can we assume that ecosystem
functions will also be preserved? We aimed to test these assumptions by disrupting
trophic interactions along natural and anthropogenic gradients of diversity with
vertebrate exclusions. In chapter two, we focus on shifts in biotic distribution that
occur naturally with elevation. Vertebrate exclusion caused strong trophic cascades
on herbivory in pristine tropical forests, but only at high altitudes. In contrast, at lower
elevations, forests showed little response to predator exclusion, with no effect on
herbivore density or subsequent plant damage. We hypothesis that habitat in the
warmer and wetter lowlands harbours higher levels of diversity within mid and low
trophic levels and this may confer some resilience to disturbance. In chapters three
and four, we investigate how distance to edge and habitat loss effects the above
processes. Edge effects significantly mediated trophic cascades, which occurred
only within the forest interior. Changes in vertebrate community composition along
interior to edge gradients are likely to be responsible for these findings. The effect of
exclusion on both arthropod densities was mediated by habitat loss, although the
proportion of plant damage was not. The generality of plant-herbivore interactions
may make them robust to perturbation, hence the neutral response of herbivory to
habitat loss. Our findings provide insight into how the provision of ecosystem
function is mediated by biodiversity loss. This information can be vital in identifying
which areas of habitat might lose functionality in the wake of disturbance. We
6
suggest that conservation efforts are refocussed to target ecosystems in which
functions are reliant on vulnerable specialist species.
species towards local and global extinctions. Often, the most sensitive species to
disturbance are the most important for the maintenance of healthy ecosystems. With
conservation efforts focussing on biodiversity, can we assume that ecosystem
functions will also be preserved? We aimed to test these assumptions by disrupting
trophic interactions along natural and anthropogenic gradients of diversity with
vertebrate exclusions. In chapter two, we focus on shifts in biotic distribution that
occur naturally with elevation. Vertebrate exclusion caused strong trophic cascades
on herbivory in pristine tropical forests, but only at high altitudes. In contrast, at lower
elevations, forests showed little response to predator exclusion, with no effect on
herbivore density or subsequent plant damage. We hypothesis that habitat in the
warmer and wetter lowlands harbours higher levels of diversity within mid and low
trophic levels and this may confer some resilience to disturbance. In chapters three
and four, we investigate how distance to edge and habitat loss effects the above
processes. Edge effects significantly mediated trophic cascades, which occurred
only within the forest interior. Changes in vertebrate community composition along
interior to edge gradients are likely to be responsible for these findings. The effect of
exclusion on both arthropod densities was mediated by habitat loss, although the
proportion of plant damage was not. The generality of plant-herbivore interactions
may make them robust to perturbation, hence the neutral response of herbivory to
habitat loss. Our findings provide insight into how the provision of ecosystem
function is mediated by biodiversity loss. This information can be vital in identifying
which areas of habitat might lose functionality in the wake of disturbance. We
6
suggest that conservation efforts are refocussed to target ecosystems in which
functions are reliant on vulnerable specialist species.
Version
Open Access
Date Issued
2019-02
Date Awarded
2022-03
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Banks-Leite, Cristina
Sponsor
National Environment Research Council (NERC) and Fundaçào de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Grant Number
N/A
Publisher Department
Life Sciences
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)