- 315 views
- 350 downloads
Species Diversity in Discrete Habitat Networks
-
- Author / Creator
- Deane, David C
-
Human activities are increasingly fragmenting the natural world. A unifying theme in this thesis is understanding the expected diversity within artificially or naturally discrete habitat networks. I start by testing a common expectation regarding the species composition of small habitat patches, which are usually assumed to support only common species. In a meta-study of 175 published studies, I found that in over 80% of datasets, some species were found only in the smallest patches. Moreover, loss of only the smallest patches comprising less than 20% of total habitat area would remove, on average, 12.7% of species, more than twice the 5.8% predicted from species-area relationships. This suggests that groups of small patches should not be assumed to comprise only common species. I then explored a second commonly held, but little tested, theory - that rapid accumulation of species when patches are combined in small-to-large size order is due to high beta diversity, driven by habitat heterogeneity. Using 38 published abundance datasets, I test competing explanations for the observed difference in the species richness of groups of small patches, relative to the largest patch using path analysis. I found that beta diversity, evenness of species abundance and size-bias in sampling efficiency explain comparable amounts of variation. Both increased and decreased evenness contributed to differences in species richness, suggesting multiple mechanisms contribute to differences in species richness between large and small patches. I conclude that assuming habitat heterogeneity accounts for the rapid accumulation of species when combining patches in small-to-large order is an over-simplification. This chapter also provides the first objective evidence that less effective sampling of larger patches could over-estimate the difference in species richness between groups of small patches and a single large patch. I next used sampling theory to develop and validate a suite of models predicting the expected number of shared species under any spatial and abundance distribution, allowing the effects of sub-division to be distinguished from the effects of habitat loss. The models were validated using empirical and simulated data and predict shared species and total species number in sub-divided habitat with high accuracy (R2 > 0.99, relative root mean square error < 0.05). Using the models, I show that only when individuals are randomly positioned will the number of species be unaffected by sub-division; any amount of intraspecific aggregation results in an increase in the expected species richness of sub-divided, relative to contiguous, habitat of equal total area. In other words, several small patches should contain more species than a single large patch as this is a probable consequence of intraspecific aggregation. Although this does not preclude some independent positive effect of sub-division on species diversity, it is not necessary to invoke such a mechanism to explain the presence of more species in sub-divided habitat. In my final data chapter, I use the new models to explore the effects of habitat loss and sub-division for different spatial and abundance distributions. I simulate the destruction of 20-90% of original habitat area, comparing the number of species that would be present if the remaining proportion of habitat was divided into 1-32 patches. This analysis showed that as the amount of sub-division of a given area increases (i.e., as the remaining habitat is broken into more, but smaller, pieces), the number of additional species reaches a maximum, indicating a diminishing ‘benefit’. Second, it showed that under the most even species abundance distributions (hereafter SAD), the loss of 90% of habitat (i.e., 90% of individuals), removed less than 3% of original species, compared with up to 40% under the least even SAD. A general prediction follows, where highly even SAD, (e.g., typical of tropical forest), could suffer few initial extinctions from habitat loss, but be vulnerable to delayed extinction, while less even SAD (e.g., typical of higher latitudes) might face the reverse situation. This thesis makes applied and theoretical contributions to conservation biology by providing insights relating directly to the SLOSS and fragmentation per se debates. From an applied perspective, it contributes new understanding relating to rapid species accumulation in small patches. The main theoretical contribution has been the application of sampling theory to predict the expected number of species under sub-division and habitat loss.
-
- Graduation date
- Spring 2020
-
- Type of Item
- Thesis
-
- Degree
- Doctor of Philosophy
-
- License
- Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.