The functional causes and consequences of freshwater biodiversity responses to environmental change

Freshwater biodiversity is increasingly threatened by the multifaceted impacts of global change. However, research on how freshwater biodiversity responds to global change has lagged behind studies on terrestrial systems and biodiversity. In this dissertation, I use data synthesis and macroecological approaches to examine the functional causes and consequences of freshwater fish responses to environmental change. In Chapter 1, I investigate how life-history and ecological traits regulate the temporal stability of freshwater fish populations. Using a global dataset of fish monitoring time series, I found that species traits directly influence the temporal stability of fish populations, consistent with expectations from life-history and ecological trade-offs. More interestingly, traits modulate the destabilizing effects of climatic variability and species richness. In Chapter 2, I expand the focus to examine the functional consequences of land-use and land-cover change on the diversity of freshwater fish communities in the tropics. To do so, I compile the first pantropical database of fish communities across gradients of land conversion. Overall, I found a decline in richness with increasing land conversion, along with a strong shift toward more pelagic and opportunistic communities. However, these changes are context-dependent, shaped by the pre-conversion vegetation type and the size of aquatic habitats or stream longitudinal position associated with fish communities. Recognizing that biases in freshwater biodiversity data—as in the data used in Chapters 1 and 2— challenge our understanding of biodiversity change, Chapter 3 investigates drivers behind the spatial biases in fish inventorying efforts in major Neotropical basins. As expected, I found that inventorying effort was greater in more accessible locations. Interestingly, inventorying effort also increased with species richness and environmental heterogeneity across sub-basins. Overall, my dissertation explores distinct but complementary lines of research that aim to improve our understanding of how freshwater biodiversity responds to global environmental change.

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