Developing and testing methods to assess species extinction risk and ecosystem degeneration

Abstract

Species worldwide are becoming increasingly threatened due to the rapid changes in climate and land use induced by human activities. The loss of species threatens the provision of food, goods and many other ecosystem services essential to the sustainability and well-being of human society. It is therefore important to monitor, assess and predict the loss of biodiversity at both the species and ecosystem levels so the need for any intervention can be determined. A major challenge to this task is a lack of consistent and scale-independent evaluation methods. My thesis strives to address this gap by testing some currently available methods and proposing improved ones to assess the endangerment status of species and the degeneration of ecosystems. In chapter two, I derived a model to estimate the loss of species abundance based on both the area of occupancy and spatial autocorrelation of occupied cells. This new model performed generally better in predictive power than an existing area-based model. In chapter three, I tested a spatial analysis tool, called a scalogram, for assessing the impact of disturbance on species extinction. Scalograms describe how the value of a metric changes with spatial scale (e.g., grain size) following some simple relationship, such as a power-law or a simple linear equation. I showed that it is feasible to estimate species extinction risk by analyzing the change in landscape metrics over spatial scales. In chapter four, I tested the hypothesis that the collapse of the power-law patch-size distribution could signal an early warning for ecosystem degeneration (i.e., desertification of grassland). I found that a power-law patch-size distribution was dependent on a species’ abundance, spatial aggregation and the spatial scale of analysis. All three factors could cause the patch-size distribution to deflect from the power-law model. Thus, I concluded that the power-law model was not suitable for indicating ecosystem degeneration. Understanding status of endangered-species and ecosystem degeneration is profoundly important in biological conservation. Methods developed in my thesis provide potentially useful tools for assessing extinction risk in the real world. The applications of these methods are expected to contribute to the study, legislation and practice in landscape management and biological conservation.