Date of Award


Degree Name

Master of Science


Geological Sciences


Elizabeth J. Walsh


As climate change continues to become more prevalent, increasing temperatures and altering precipitation patterns will disrupt the environmental balance of ecosystems and spark the imminent threat of a 6th mass extinction event. Many researchers believe this has already begun, as losses for numerous taxonomic clades have been well documented; however, the loss of invertebrates is still unknown and may be much more severe than those of other animal clades. A significant factor contributing to the shortfall of invertebrate biodiversity loss is rooted in the lack of understanding of the diversity and distribution of these animals. There is still much to be learned about North America's freshwater invertebrate community assemblages and the environmental factors that influence their species richness. Temporary rock pools occur at high densities on rock formations, have unique spatial configurations, lack hydrological connections, are subjected to unpredictable hydroperiods, and embody very similar environmental constraints. Rock pools are also small, pristine, and structurally simple systems. These characteristics serve as model systems for investigating specific environmental constraints associated with latitude or hydroperiod and how these factors influence community assemblages. In addition, temporary rock pools also provide valuable insights into the quantification of ecological processes that are often challenging and sometimes impossible to explore in larger freshwater systems. There is still a need for research on the temporary rock pool community assemblages in the Chihuahuan Desert, including whether zooplankton species richness increases or decreases with latitude and/or hydroperiod. Other than the work of Walsh and colleagues, most existing studies on rock pool zooplankton communities have not included Rotifera, one of the dominant groups present in these temporary pools. To better understand the distribution of freshwater aquatic invertebrate communities, I explored temporary rock pool species richness in six sample locations throughout a Chihuahuan Desert latitudinal gradient of 26°N - 31°N. Each sample location consisted of three spatially separated subsites, and a minimum of three sets of rock pools at each subsite for a total of 61 ephemeral rock pools. For each rock pool, the presence-absence of aquatic invertebrates was determined to produce estimates of alpha, beta, and gamma diversity. Water quality, when possible, and other environmental parameters were assessed to explore influences on community structure. I predicted species richness would increase with hydroperiod and decrease with latitude, as well as that there would be similarities in taxa that inhabit these temporary environments. A total of 56 taxa were identified, including 13 families, 19 genera, and 27 species belonging to the phylum Rotifera. Rock pools were categorized into four hydroperiod levels for the analyses. As predicted, species richness was positively correlated with hydroperiod. There was no correlation between alpha, beta, or gamma diversity with latitude. Analysis of Sorenson's diversity index revealed higher community dissimilarity comparing sub-communities (β = 0.76) than sample location meta-communities (β = 0.61). There was a nestedness pattern, indicating that species assemblages were composed of non-random nested subsets of communities with greater species richness. These findings confirm and extend past results showing that freshwater zooplankton species richness is higher in pools with longer hydroperiods, and diversity is homogenized over larger geographic scales. Newly sampled sites contained several taxa not previously reported, indicating that additional sites will add to the estimated richness. The results will help aid in the conservation prioritization of Chihuahuan Desert freshwater habitats and establish ecological baselines for temporary environments.




Recieved from ProQuest

File Size

102 p.

File Format


Rights Holder

Joseph Lee McDaniel