Schaefer Lab

Hybrid Zones as natural laboratories of evolution -

Habitat heterogeneity, strong ecological gradients and niche differentiation are expected to increase species diversity and the probability of coexistence among sister species. Contact zones, where similar species coexist and hybridize, have long been of interest in studies addressing a number of hypotheses regarding the evolution and maintenance of species boundaries. The ecology of contact zones is not as well understood. Because they contain recently diverged coexisting species, they are ideal systems for testing a number of ecological hypotheses. A fundamental question in the ecology of contact zones is how they are structured and if that structure is predictable based on the strength and nature of existing ecological gradients. River networks are characterized by linear and predictable ecological gradients from headwaters to large river habitat (River Continuum Concept). Fishes in the Fundulus notatus species complex segregate along these stream gradients in replicate hybrid zones throughout their broad range. Lab research in this area seeks to understand the evolutionary ecology of this group through understanding the dynamics of these hybrid zones.

Geographic range of F. notatus (yellow) and F. olivaceus (blue). Credit to S. Clark for correcting colors.

Evolutionary Physiology

The inextricable link between temperature, physiology, and ecology of ectotherms can result in complex responses to environmental variability. The need for understanding these physiological, ecological and evolutionary responses to temperature is increasingly urgent as rates of climate change increase. Aquatic ectotherms are particularly vulnerable to temperature changes due to the high thermal conductivity and specific heat of water. It is also widely accepted that geographic ranges and range expansion of ectotherms is limited by local thermal regimes. Lab research in this area deals with the evolutionary and ecological consequences of tolerance and performance within an energetic framework.

Physiological optima of F. notatus and F. olivaceus from hatching success thermal reaction norms.

Community Ecology, Disturbance, Invasions and Long Term Patterns -

Fluctuations in abundance and site occupancy by species lead to variability in community composition over time, both in terms of the species present and their relative abundance. Demographic and environmental stochasticity combine with species interactions to yield considerable natural variability in community structure. Ecologists have long been interested in how the communities vary space, determining the association between the community composition and environmental conditions, or how communities within sites vary over time. Lab research in this area involves studying the range of natural temporal variability of fish assemblages to address a range of questions.

Conservation of Threatened Fishes -

The southeastern United States has a diverse fish fauna. The five states with the most fish diversity (Alabama, Tennessee, Georgia, Kentucky and Mississippi) are all located in the Southeast. At the same time, habitat alterations and other pressures have threatened a number of these species. For a number of these species, there are fundamental knowledge gaps (missing information on life history and ecology) that prevent effective management and conservation of these species. Lab research has been aimed at providing some of this information. We have worked with Alabama shad (Alosa alabamae), alligator gar (Atractosteus spatula), the bayou darter (Etheostoma rubrum) and the Pearl darter (Percina aurora).
Alosa alabamae

Research Infrastructure

– At USM, there are abundant natural and experimental resources to do the research described above. The USM Ichthyological Collection contains over 40,000 cataloged lots and is one of the largest fish collections in the state of Mississippi. For experimental work, a set of stream mesocosms is available at the Department of Biological Sciences Lake Thoreau Environmental Center. There is also a 3,000 square foot wetlab on the Hattiesburg campus with numerous aquaria and environmental chambers. Finally, USM is situated in the Pascagoula River drainage that provides an optimal system for this type of research. The Pascagoula is the largest remaining undammed basin within the continental United States.
Stream mesocosms at the Lake Thoreau Environmental Reasearch Center