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Dr. Kristen Work – Professor of Biology
Department of Biology
How do proximity, water body size, vegetation coverage, and presence of predators affect odonate assemblages in Ocala National Forest wetlands and ponds?
For any organism, its presence in an ecosystem depends upon its ability to migrate to that system and persist within it. In many areas, aquatic organisms may be more limited in their distributions because they cannot migrate through inhospitable dry land between their habitats. Odonates(dragonflies and damselflies) represent organisms that have intermediate dispersal abilities; adults can fly between habitats, but their reproduction and juvenile stages are limited to water habitats. Therefore, odonate assemblages might show regional fidelity, but overlap on a local scale. In this study, we tested whether odonate assemblages would be more similar in closely located ponds than in more distant ponds. To test this hypothesis, we collected both adult and juvenile animals at 16 wetlands/ponds (hereafter called ponds) in four groups running southeast to northwest in Ocala National Forest on June and August 2023 (we also had samples from May and August 2021). We collected all available adults with aerial nets (butterfly nets) for 10 minutes, sacrificed them in acetone charged jars, and recorded the animals that we saw but could not catch. We collected the juveniles with 10 1-m dipnet drags, sorted the collected material to remove the odonates, and preserved them in alcohol. We also recorded the presence/absence or number (the second trip) of crayfish, fish, and tadpoles that we caught inadvertently. We returned these animals to the ponds. We also measured a variety of environmental variables. In the field, we measured the temperature and dissolved oxygen with a YSI Pro multiparameter meter and we measured the depth with a depth sounder and transect tape. In the laboratory, we measured the area of the ponds and the plant coverage using ImageJ analysis of Google Earth photos. We identified all the animals to species and calculated the odonate density, species richness, and diversity of each pond. We evaluated similarities in close and distant ponds by comparing each pond’s similarity to its neighbors to its similarity to the more distant ponds with a paired t-test. We evaluated the distinctiveness of the assemblages using nonmetric multidimensional scaling (nMDS) followed by analysis of similarity (ANOSIM) in PRIMER and the potential effect of the environmental variables using stepwise multiple regression in R. The number of individuals collected varied widely with pond size, but the diversity varied much less. Odonate assemblages were, in fact, slightly more similar if they were within the same pond group, but this trend only applied to dragonflies (our catch of damselflies was lower). Among the four pond groups, the assemblages that were most similar were from a group that occurred in a broad grassland with only few trees between the ponds; these ponds were more similar to each other in shape and plant cover and they were relatively close together with few obstacles to migration between ponds. However, most of the environmental variables that we collected were important for either dragonfly or damselfly assemblages on one of the dates sampled: pond size, distance between ponds, distance to the forest, temperature, dissolved oxygen, present of lilies or grasses, presence of odonate predators (some odonates eat each other), presence of other invertebrate predators (crayfish), or presence of vertebrate predators (fish and tadpoles). These results suggest that dispersal and the physical and biological conditions of the ponds determine odonate structure in Ocala ponds. Given the pressure on ecosystems due to development and the limited research on odonates in Florida, we hope that these results will help to contribute to the maintenance of diversity in Florida.
Dr. Kirsten Work is a freshwater ecologist with wide-ranging interests and skills. After stints in the upper Midwest, Alaska, Oklahoma studying lake plankton and fish, she shifted gears to invertebrates and fish in Florida springs and wetlands. She has published on zooplankton assemblage ecology, spring ecology, spring integrity, and most recently edited a special issue of a journal on spring conservation. Her broad geographic background gives her a broad perspective on freshwater ecology and conservation across differences in topography, geology, and land uses. She has taught introductory biology, statistics, limnology, conservation biology, biodiversity and conservation of tropical systems, and research courses since 2000.