Survey of Biogeography and Community Ecology Surrounding Etheostoma radiosum in Northeast Texas and Southeast Oklahoma

Document Type


Degree Name

Master of Science (MS)


Biological and Environmental Sciences

Date of Award

Spring 2023


The orange-bellied darter, Etheostoma radiosum, is a small benthic fish found in the Red River system in Oklahoma, Arkansas, and Texas. Populations in Texas serve as the functional southern edge of the species geographic range and are rare in the region. Surveys were done to determine spatial occupancy patterns for E. radiosum in Texas and to examine specific habitat and community associations of occupied sites. Streams in Texas were also compared with streams in Oklahoma to assess potential niche shifts. Forty-six streams (thirty-four in Texas; twelve in Oklahoma) were sampled for fish communities and stream environmental characteristics in 2021 and 2022. E. radiosum was rare in Texas sites, occurring in five out of the thirty-four streams. This species was more common in Oklahoma (ten out of twelve locations). Community patterns were assessed with non-metric multidimensional scaling (NMDS) and analysis of similarities (ANOSIM). There were three significantly different community groups in the data: Oklahoma present, Texas present, and absent (R = 0.361, p < 0.00001). Environmental variable data was fitted onto the NMDS ordination with the envfit function of the R package vegan, to determine which environmental variables significantly relate to the observed patterns of community differences. The analysis identified nine significant environmental variables, and E. radiosum present sites specifically had less mud, more coarse substrates, higher dissolved oxygen, higher slope, more riffles, and more annual flow stability. The Texas present sites were intermediate between the other two groups in the ordination, indicating that the sites in Texas are suboptimal in gradient conditions compared with their core distribution in Oklahoma. Flow stability and coarse substrates with riffles were the main drivers of E. radiosum presence in the data, and specifically periodic drought (less stable flows) and rarity of coarse substrates in Texas tributaries likely combine to limit the occupancy patterns for this species in the state.


Bjorn Schmidt

Subject Categories

Ecology and Evolutionary Biology | Life Sciences