Disturbance Macroecology PDF Download

Author: Erica A. Newman
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Languages : en
Pages : 148

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Book Description
Little is known about how metrics of biodiversity and abundance scale in ecologically disturbed and disrupted systems. Natural disturbances have a fundamental role in structuring ecological communities, and the study of these processes and extension to novel ecological disruptions is of increasing importance due to global change and mounting human impacts. Numerous studies have demonstrated the importance of natural disturbance in determining basic ecological properties of an ecosystem, including species diversity, membership, and relative abundances of those species, as well as overall productivity. Although estimating ecological metrics at both the species and community level is of critical importance to conservation goals, predicting the impacts of disturbance and disruption, including anthropogenic changes, on ecosystems is a major problem for ecological theory for several reasons. Disturbances are diverse in type, create patches that are internally heterogeneous, interact with site-specific disturbance legacies, and have different effects over multiple spatial and temporal scales. In contrast, empirical studies providing the basis for development of models tend to focus on short time-scales and relatively homogeneous systems with steady-state dynamics. Sites that experience single disturbances or are part of disturbance regimes also pose a challenge to ecological theory because they represent open, non-equilibrium systems that are not tractable with equilibrium mathematics. Additionally, the spatial scale at which a disturbance is studied will affect the conclusions that are drawn about communities or their component species. Nevertheless, the ubiquity and importance of disturbance to ecosystems continues to motivate a search for generality in disturbance and landscape ecology. In this dissertation, I apply an information entropy based theory of macroecology to ecosystems in transition, or have otherwise experienced ecological disruption. This leads to comparable results between systems, and forms a basis for cross-system comparisons of ecosystems in transition. The maximum information entropy inference procedure (MaxEnt) has been proven to produce the least-biased estimates of a probability distribution, given prior knowledge of a system. Empirical values make up the prior knowledge of the system, and constrain the mean, variance, or higher moments of a given distribution. An extension of the MaxEnt procedure, the Maximum Entropy Theory of Ecology (METE) takes a macroecological approach to estimating plot- to landscape- to biome-scale species diversity, abundance, and energetics metrics, using only the relationships between four non-adjustable state variables S0 (total species), A0 (area under consideration), N0 (total abundance), and E0 (total metabolic energy), and no adjustable parameters to characterize the scaling of diversity and abundances of species in a system. Until this work, METE has mainly been tested in steady-state and minimally disturbed systems. In Chapter 1, "Disturbance macroecology: a comparative study of plant species' abundances and distributions in different-age post-fire stands of Bishop pine (Pinus muricata)," I investigate how metrics of biodiversity and abundance are scale in a plant community that is largely structured by a dominant, disturbance-dependent species. We target two different-aged stands in a region of high wildfire activity, one a characteristically mature stand with a diverse understory, and one more recently disturbed by a stand-replacing fire 17 years previously. We compare the stands using various macroecological metrics of species richness, abundance and spatial distributions that are predicted by METE, which does not rely on steady-state or equilibrium assumptions, and is therefore well-suited to be a null model for ecosystems in transitional states. Ecological patterns in the mature stand more closely match METE predictions than do data from the more recently disturbed stand. This suggests METE's predictions are more robust in late successional, slowly changing, or steady-state systems than those in rapid flux with respect to species composition, abundances, and body sizes. These findings highlight the need for a macroecological theory that incorporates natural disturbance and other ecological perturbations into its predictive capabilities, because most natural systems are not in a steady state. In Chapter 2, "Macroecology for management: Testing an information-entropy-based theory of macroecology against anthropogenic disruption of high-Sierra meadows, I investigate the extent to which anthropogenic changes to an ecosystem, in the form of grazing by large, introduced herbivores, are detectable using METE, and small (