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Sophia Passy, associate professor of biology
Sophia Passy, associate professor of biology

A biologist from The University of Texas at Arlington is studying why the populations of some species are more adversely affected than others by various harmful factors in freshwater environments.

Sophia Passy, associate professor of biology, received a two-year, $199,997 grant from the National Science Foundation’s Division of Environmental Biology for her project, titled “EAGER: Global assessment of the causes and consequences of commonness and rarity in freshwaters”.

Human activity has caused a decline in global biodiversity through resource overexploitation, habitat modification, and introduction of non-native species. When rare species are lost, communities exhibit decreased functionality and provide devalued services to humans, which is an environmental and a socioeconomic problem.

“Although biodiversity loss is global and affects all ecosystems, biodiversity in freshwaters is threatened by much higher extinction rates compared to terrestrial habitats,” Passy said. “Therefore, a better understanding of the causes and extent of rarity in freshwaters is urgently needed.”

Passy and students in her laboratory are using the species abundance distribution (SAD) – a measure of the relative abundances of common and rare species within a sample or ecological community – to assess species rarity.

“Although the SAD has been investigated for more than 70 years, little is known about the underlying mechanisms that determine the patterns of abundance inequality,” Passy said.

In order to address this knowledge gap, Passy and her students are developing a novel framework which predicts the response of the SAD in freshwater habitats along environmental and spatial gradients. They are also investigating how the SAD affects regional biodiversity. The study also will inform decisions for watershed management and biodiversity preservation by explaining the causes of rarity in species targeted for conservation.

First results from this research reveal that in the United States, biodiversity and the SAD of diatom communities — unicellular algae and some of the most important producers in stream ecosystems — are strongly affected by temperature seasonality, with higher seasonality (a higher temperature difference between warm and cold months) contributing to more diverse communities with a more balanced distribution of common and rare species. As temperature seasonality is expected to decrease with global warming due to warming of the cold months, diatom biodiversity is likely to decline and species rarity to increase with potential negative consequences for primary production and maintenance of higher trophic levels.  

The project is providing research training for one postdoctoral associate and two graduate students. Katrina Pound, a postdoctoral associate in Passy's lab, is examining what environmental factors constrain the distribution of freshwater species across the contiguous United States. Her research suggests that climate exerts the strongest influence on the distributions of multiple freshwater organismal groups, including diatoms, insects, and fish, surpassing the effects of water chemistry and watershed characteristics. These results indicate that climate change may alter species ranges and biodiversity of freshwater ecosystems to a greater extent than other serious anthropogenic impacts, such as water fertilization and pollution.

In collaboration with a team of international researchers, William Budnick, a Ph.D. student in Passy's lab, is investigating how regional biodiversity of diatoms, macroinvertebrates, and fish, collected from streams in the United States, Canada, and France, is affected by land use. His findings indicate that agricultural land use leads to loss of regional biodiversity across all studied groups of organisms, but the mechanisms driving this process are group- and region-specific, emphasizing the need for targeted conservation efforts.

NSF’s EAGER (Early-concept Grants for Exploratory Research) program was designed specifically for innovative research – potentially transformative or exploratory projects that examine new subjects, different methods, or interdisciplinary approaches.

Clay Clark, professor and chair of the UTA Department of Biology, said that Passy’s research has the potential to provide scientists with knowledge about why species are abundant in some environments but scarce or nonexistent in others. The project also advances research in global environmental impact, one of the main themes of UTA’s Strategic Plan 2020: Bold Solutions | Global Impact.

“Dr. Passy’s work could help ecologists learn a great deal about the underlying causes of the distribution of freshwater species abundance and thus allow for more effective methods to protect the biodiversity found in these environments,” Clark said.

Passy received an M.S. in Biology (1986) from Sofia University in Bulgaria. She earned a Ph.D. in Ecology from Bowling Green State University in Ohio in 1997 and held postdoctoral positions at the University of Minnesota Medical School and the Rensselaer Polytechnic Institute in New York before coming to UTA in 2001.