| dc.description.abstract | **Please note that the full text is embargoed until 8/1/2024** ABSTRACT: The extent of human influences on the environment and biodiversity has led to naming our current time period the Anthropocene. A primary way in which humans impact biodiversity is through habitat modification. Despite the knowledge that habitat modification is negative for many species, we still don’t understand why some species are able to persist despite habitat modification while others do not. In my first chapter I used a trait-based approach to understand what determines species’ sensitivity to habitat modification. Trait-based approaches from different regions often disagree on the importance of the same traits, and I thought climate and land use change severity may account for some of these discrepancies. I set out to test the role of microhabitat use, climate and land use change severity in determining how species respond to habitat modifications. I used anuran abundance data from 18 studies across tropical forests, in conjunction with trait data (microhabitat use and reproductive mode). I found that microhabitat use greatly impacts species’ sensitivity to habitat modification, particularly that species vertical niche is important as species’ abundance tends to track the availability of their preferred vegetative strata. Arboreal anurans are most sensitive to conversion to land uses which lack vegetative strata, however the extent to which arboreal anurans are sensitive varies with climate. In warmer regions arboreal species are not as sensitive to habitat modification as terrestrial species, as their arboreal nature may have pre-adapted them to the warmer conditions associated with habitat loss. The finding that climate influences trait-based responses to habitat modification is novel and shows that conservation efforts need to incorporate climate context into planning. In my next chapter (chapter 3) I assess what accounts for variation between communities in sensitivity to habitat modification. Previous research has demonstrated that populations and communities vary in their sensitivity to habitat modification, and contemporary factors such as climate account for some of this variation. Here I focus on how historical factors
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may also contribute to this variation, I test if early humans have contributed to the variation in community sensitivity to land use change. I test the extinction filter hypothesis, using early humans as a filter, which may have already removed sensitive species from communities. I used the PREDICTS database to obtain bird community in different land uses from 54 studies across the world. I found that early humans impact community sensitivity, areas with a greater history of human presence, tend to be less sensitive to habitat modification. This reduced sensitivity to habitat modification comes from a decrease in the number of species found in primary vegetation, rather than an increase in species able to tolerate habitat modification. These results suggest that it is important to consider human history when considering patterns of diversity and/or assessing which communities are most critical to protect, as sensitive species are more likely to occur in areas with low histories of human presence. In my last chapter (chapter 4), I focus on species interactions, as a potential factor which may be causing species to decline. I assessed the population trends of a common lizard, the prairie lizard (S. consobrinus), which appears to be in decline, and a closely related species, the Texas Spiny Lizard (S. olivaceus). Occurrence data from the last 100 years reveals that S. consobrinus is declining, while S. olivaceus is increasing in relative abundance. I grouped the data into pseudo-sites to assess the role of climate change, land-use change, and species interactions in the decline of S. consobrinus. I found that climate alone does a poor job of predicting the current distribution of S. consobrinus, and that presence of S. olivaceus and amount urbanization are much better predictors of S. consobrinus occurrence. S. olivaceus seems to be critical in contributing to the decline of S. consobrinus, and co-occurrence between the two species has become increasingly infrequent through time. To validate that these results in patterns of co-occurrence are representative of natural communities, I performed 176 surveys spread across the distribution of S. consobrinus in
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Texas. Community surveys mirrored occurrence data and suggest that presence of S. olivaceus leads to absence of S. consobrinus in habitat it would otherwise likely occupy. Observations of the two species in the field revealed major shifts in habitat use by S. consobrinus in the presence of S. olivaceus, occupying habitat three times as open in areas which also possess S. olivaceus when compared to alone. Finally, to confirm that competition is occurring I conducted competition trials between the two species and found that S. olivaceus is the superior competitor when compared to S. consobrinus. Aggressive behaviour by S. olivaceus leads to frequent retreats by S. consobrinus, and greatly increased frequency of S. consobrinus hiding compared to when S. consobrinus is not present. Across all data, results suggest that S. olivaceus is competing with S. consobrinus, and that this contributes to the decline S. consobrinus in central and south Texas. | |
