Mary Freeman, Ph.D.
Mary Freeman is a research ecologist with the Patuxent Wildlife Research Center and is stationed in Athens, GA. She received a B.S. in biology (1979), a M.S. in entomology (1982) and a Ph.D. in forest resources (1990) from the University of Georgia. Before joining Patuxent, Mary conducted research for the U.S. Fish and Wildlife Service and the National Biological Service in Auburn, AL (1992-1996). Mary serves as affiliate faculty at the Odum School of Ecology, University of Georgia, and on the graduate faculties at the University of Georgia and Auburn University.
Science and Products
The Challenge: Ecologists have shown that many ecological processes in rivers, including organism growth, reproduction, survival and dispersal, are attuned to natural patterns of streamflow variability. However, to predict how riverine biota will respond to flow alteration caused by, for example, water diversions and dam operations, ecologists need to understand the mechanisms through which changes in streamflow affect plant and animal populations. Therefore, we are conducting field studies and analyses to test hypothesized effects of streamflow variability on population (survival, reproduction, extirpation, colonization) and trophic (primary production and consumption) dynamics.
The Challenge: The DOI WaterSMART (Sustain and Manage America’s Resources for Tomorrow) initiative is developing data and tools to help water managers identify current and future water shortages, for humans and for freshwater ecosystems. Fishes, for example, can decline in diversity and abundance when streamflow becomes too low, for too long. However, ecologists find that effects of declining streamflow can vary depending on stream characteristics and on traits of local species, confounding predictions of ecological outcomes. Scientists thus need data on ecological responses to low streamflow in differing physical and biological contexts to better inform water management decisions.
Local adaptation in Trinidadian guppies alters stream ecosystem structure at landscape scales despite high environmental variability
While previous studies have shown that evolutionary divergence alters ecological processes in small-scale experiments, a major challenge is to assess whether such evolutionary effects are important in natural ecosystems at larger spatial scales. At the landscape scale, across eight streams in the Caroni drainage, we found that the presence of...Simon, Troy N.; Bassar, Ronald D.; Binderup, Andrew J.; Flecker, Alex S.; Freeman, Mary C.; Gilliam, James F.; Marshall, Michael C.; Thomas, Steve A.; Travis, Joseph; Reznick, David N.; Pringle, Catherine M.
Ecology of the macrophyte Podostemum ceratophyllum Michx. (Hornleaf riverweed), a widespread foundation species of eastern North American rivers
Podostemum ceratophyllum, commonly called Hornleaf Riverweed, occurs in mid-order montane and piedmont rivers of eastern North America, where the plant grows submerged and attached to rocks and stable substrates in swift, aerated water. Multiple studies, mostly conducted in the southern portions of the plant’s range, have shown that Podostemum can...Wood, James; Freeman, Mary C.
Organic-matter retention and macroinvertebrate utilization of seasonally inundated bryophytes in a mid-order Piedmont River
There is increased understanding of the role of bryophytes in supporting invertebrate biomass and for their influence on nutrient cycling and carbon balance in aquatic systems, but the structural and functional role of bryophytes growing in seasonally inundated habitats is substantially less studied. We conducted a study on the Middle Oconee River...Wood, James; Pattillo, Meryom; Freeman, Mary C.
Integrating modeling, monitoring, and management to reduce critical uncertainties in water resource decision makingPeterson, James T.; Freeman, Mary C.
Ecological resistance in urban streams: the role of natural and legacy attributes
Urbanization substantially changes the physicochemical and biological characteristics of streams. The trajectory of negative effect is broadly similar around the world, but the nature and magnitude of ecological responses to urban growth differ among locations. Some heterogeneity in response arises from differences in the level of urban...Utz, Ryan M.; Hopkins, Kristina G.; Beesley, Leah; Booth, Derek B.; Hawley, Robert J.; Baker, Matthew E.; Freeman, Mary C.; Jones, Krista L.
Application of effective discharge analysis to environmental flow decision-making
Well-informed river management decisions rely on an explicit statement of objectives, repeatable analyses, and a transparent system for assessing trade-offs. These components may then be applied to compare alternative operational regimes for water resource infrastructure (e.g., diversions, locks, and dams). Intra- and inter-annual hydrologic...McKay, S. Kyle; Freeman, Mary C.; Covich, A.P.
Using occupancy modeling and logistic regression to assess the distribution of shrimp species in lowland streams, Costa Rica: Does regional groundwater create favorable habitat?
Freshwater shrimps are an important biotic component of tropical ecosystems. However, they can have a low probability of detection when abundances are low. We sampled 3 of the most common freshwater shrimp species, Macrobrachium olfersii, Macrobrachium carcinus, and Macrobrachium heterochirus, and used occupancy modeling and logistic...Snyder, Marcia; Freeman, Mary C.; Purucker, S. Thomas; Pringle, Catherine M.
Shoal basses: A clade of cryptic identity
Shoal basses are a cryptic clade composed of Micropterus spp. restricted to the Apalachicola River system and three southeastern Atlantic slope river drainages in the southeastern United States. This reciprocally monophyletic clade includes the Shoal Bass M. cataractae (endemic to the Apalachicola River system), the Chattahoochee Bass M....Freeman, Byron J.; Taylor, Andrew T.; Oswald, Kenneth J.; Wares, John; Freeman, Mary C.; Quattro, Joseph M.; Leitner, Jean K.
Evidence of population resistance to extreme low flows in a fluvial-dependent fish species
Extreme low streamflows are natural disturbances to aquatic populations. Species in naturally intermittent streams display adaptations that enhance persistence during extreme events; however, the fate of populations in perennial streams during unprecedented low-flow periods is not well-understood. Biota requiring swift-flowing habitats may be...Katz, Rachel A.; Freeman, Mary C.
Diel patterns and temporal trends in spawning activities of Robust Redhorse and River Redhorse in Georgia, assessed using passive acoustic monitoring
The conservation of imperiled species depends upon understanding threats to the species at each stage of its life history. In the case of many imperiled migratory fishes, understanding how timing and environmental influences affect reproductive behavior could provide managers with information critical for species conservation. We used passive...Straight, Carrie A.; Jackson, C. Rhett; Freeman, Byron J.; Freeman, Mary C.
Stream classification of the Apalachicola-Chattahoochee-Flint River System to support modeling of aquatic habitat response to climate change
A stream classification and associated datasets were developed for the Apalachicola-Chattahoochee-Flint River Basin to support biological modeling of species response to climate change in the southeastern United States. The U.S. Geological Survey and the Department of the Interior’s National Climate Change and Wildlife Science Center established...Elliott, Caroline M.; Jacobson, Robert B.; Freeman, Mary C.
Passive acoustic monitoring to detect spawning in large-bodied catostomids
Documenting timing, locations, and intensity of spawning can provide valuable information for conservation and management of imperiled fishes. However, deep, turbid or turbulent water, or occurrence of spawning at night, can severely limit direct observations. We have developed and tested the use of passive acoustics to detect distinctive acoustic...Straight, Carrie A.; Freeman, Byron J.; Freeman, Mary C.