Daniel J. Leavitt

Disassembly of a dune‐dwelling lizard community due to landscape fragmentation

Landscape fragmentation alters patterns of landscape structure that affect quality and configuration of habitats, and disrupts population dynamics and persistence of species. Community disassembly, a process of community change due to nonrandom species losses and declines, is occurring worldwide as a result of landscape fragmentation, habitat loss, and habitat degradation. We carried out a comparative study at 27 trapping sites designed to characterize how fragmentation affects community structure in a dune-dwelling lizard community. Lizard communities in non-fragmented sites demonstrated nested community structure. Conversely, lizard communities at sites fragmented by roads and well pads from oil and gas development had consistently lower abundance of two species, and demonstrated random community structure. Species loss and lower abundance of species at fragmented sites suggested a pattern of community disassembly. The dunes sagebrush lizard (Sceloporus arenicolus), an ecological specialist, and the lesser earless lizard (Holbrookia maculata) were present on most non-fragmented sites. However, neither species was present on more than half of the fragmented sites, and their abundances were much lower than on non-fragmented sites. We attributed reduced species diversity on fragmented sites to quantitative differences in landscape configuration compared to non-fragmented sites. Specifically, both size and shape of sand dune blowouts differed between non-fragmented and fragmented sites. Fragmented sites possess more large patches of open sand and barren ground and fewer, smaller, and more dispersed shinnery dune blowouts. Patterns of occurrence and relative abundance suggest S. arenicolus and H. maculata were sensitive to these patch-scale attributes. In this ecosystem, landscape-scale fragmentation appears to influence landscape configuration and community disassembly at the patch-scale. Our findings allow us to disentangle drivers of species loss and enhance our understanding of the processes of community disassembly in fragmented landscapes.

Diet of Nonnative Hyla cinerea in a Chihuahuan Desert Wetland

Abstract Hyla cinerea recently introduced to a Chihuahuan Desert wetland in Big Bend National Park, Texas consumed a variety of terrestrial arthropods. We investigated its diet to analyze a component of colonizing potential for this species. Of 105 individuals analyzed, we found a total of 194 prey items representing 13 unique categories. The most important prey, determined with a quotient that combines volume and count with frequency, were beetles, cockroaches, grasshoppers and crickets, ants, and spiders. We documented the first occurrence of Scorpiones in the diet of H. cinerea, which demonstrates this invaders ability to exploit novel resource types outside of its native range. In comparison to other dietary studies conducted on H. cinerea, this nonnative population feeds on a similar diversity of prey in equal proportions. This analysis represents a first step into evaluating ecological effects of this nonnative population of H. cinerea.

Diet of Barn Owls (Tyto alba) in Northern Belize

Abstract Diet of the barn owl (Tyto alba) has been well studied in temperate regions of the world, but there is a notable paucity of dietary data from the Neotropics. In this study, we examined diet of barn owls at Gold Button Lagoon in northern Belize. Pellets and prey remains were collected at roosting sites during 1997–1998. Diet was composed primarily of small mammals. Sigmodon hispidus was the most common prey in terms of frequency of occurrence and biomass, with lesser numbers of other rodents being consumed. Similar to other reports for the Neotropics, barn owls in our study consumed relatively larger prey than conspecifics inhabiting temperate regions. Birds and amphibians were a minor component of diet.

Post-grazing changes of vegetation in Big Bend National Park, Texas: a 50-year perspective.

Abstract This research compared surveys of vegetation that were conducted in Big Bend National Park, Brewster County, Texas, during 1955–1960 and 1968–1969 with data collected in 2005 and 2006. Comparisons were based on percentages of cover and flora at five study sites. Results suggest some increases and decreases in certain types of vegetative cover since creation of the park, although no trend was consistent across elevations and years. Sites at lowest and highest elevations had significant increases in shrubs. Except for one, all sites had significant differences in total cover. Some species had changed in overall abundance. Lehmann lovegrass (Eragrostis lehmanniana) was becoming a dominant grass in foothills of the Chisos Mountains and surrounding Chihuahuan Desert. In contrast, leatherstem (Jatropha dioica), fragrant sumac (Rhus trilobata), tarbush (Flourensia cernua), four-wing saltbush (Atriplex canescens), desert hackberry (Celtis pallida), and Mexican mock vervain (Glandularia bipinnatifida) had disappeared from some, or all, locations where they were recorded previously.

Functional distance and establishment of non-native species with complex life cycles

More than 80% of animals have complex life cycles and undergo distinct changes in ecology and morphology during development. The strength and type of factors regulating each life-stage may differ as an organism may occupy different niches during ontogeny. We examined the functional distance at larval and adult life-stages of two non-native anurans (Green Tree Frog [Hyla cinerea] and Bullfrog [Lithobates catesbeianus]) that have established in a Chihuahuan Desert anuran assemblage in Big Bend National Park. Both life stages of both non-native species occupied niche space outside of the native assemblage. At the larval stage, the ability of the tadpoles to utilize permanent aquatic habitats and coexist with predatory fishes differentiated the non-native species from the majority of the native species that are restricted to temporary pools. At the post-metamorphic life stage, each species appears to have established by exploiting unoccupied habitat and trophic niches in the recipient community. The arboreal habits of H. cinerea may enable it to utilize resources in microhabitats that are otherwise not used by native species because arboreal frogs are absent from this native assemblage. The large body size of post-metamorphic L. catesbeianus may enable it to utilize larger food resources that are otherwise unavailable to the smaller-bodied natives. Separate comparison of larval and adult functional traits between non-natives and the native community may help predict their potential establishment or invasion success as well as aid in the development of stage-specific control or eradication efforts.

The geographic range of Uma scoparia Cope, 1894 (Squamata: Phrynosomatidae) in Arizona

Surveys dedicated to better describing the distribution of Uma scoparia in Arizona are reported. These extend this species’ distribution in La Paz County, Arizona, 20 km further to the south than previously described. Six records on the outside of a confused range are presented alongside data from 170 captures within this range. This species is well known from California but its Arizona distribution is little understood and less well studied than other members of its genus. Concern about the conservation status of the disjunct Arizona population makes this report valuable to resource managers. Lizards were observed with ease and in large numbers at nearly all sites surveyed.

A Patternless Morph of the Marbled Whiptail (Aspidoscelis marmorata; Squamata: Teiidae) in New Mexico

Abstract The marbled whiptail (Aspidoscelis marmorata) is a common lizard within the Chihuahuan Desert of the United States–Mexico borderlands. We report a patternless female from the Mescalero–Monahans Shinnery Sands Ecosystem in southeastern New Mexico. One previous record of this pattern has been noted in the literature and this unique morphology has not been investigated thoroughly. Resumen El huico texano (Aspidoscelis marmorata) es una especie de lagartija común en el desierto de Chihuahua en la frontera México-Estados Unidos. Reportamos la ocurrencia de una hembra sin patrón en el ecosistema arenoso Mescalero–Monahans en el sureste de Nuevo México. Un patrón similar al reportado en este estudio se presenta en la literatura, pero este patrón morfológico único no ha sido investigado a fondo.

Assemblages of rodents in riparian forests along the Rio Grande in Big Bend National Park, Texas: current and historic insights on the effects of invasion by saltcedars.

Abstract Comparisons of assemblages of rodents along the Rio Grande in Big Bend National Park, Brewster County, Texas, were made using recent (2009–2010) and historic (1977) data to evaluate the effects of invasion by saltcedars (Tamarix). Comparisons of abundances and species of rodents between sites with mesquites (Prosopis), cottonwoods (Populus), or saltcedars revealed no significant difference between habitats. Comparisons of recent and historic assemblages of rodents suggested low turnover of species, but structure of assemblages differed between studies. The western harvest mouse (Reithrodontomys megalotis) was an addition to the riparian fauna and neither the silky pocket mouse (Perognathus flavus) nor Nelsons pocket mouse (Chaetodipus nelsoni) was captured during the recent assessment. Differences in assemblages may be caused by shifts in riparian plants toward a more closed canopy or by recolonization following flooding. Resumen Comunidades de roedores a lo largo del río Grande en el Parque Nacional Big Bend, condado de Brewster, Texas, fueron comparadas usando registros recientes (2009–2010) e históricos (1977) para evaluar los efectos de la especie invasora tamarisco (Tamarix). Comparaciones de las especies y abundancias de roedores en lugares con mezquites (Prosopis), álamos (Populus) y tamariscos no revelaron diferencias significativas entre estos hábitats. Comparaciones de los registros recientes y de los históricos, sugirieron baja tasa de cambio de especies, pero la estructura de estas comunidades varió entre los estudios. El ratón cosechero común (Reithrodontomys megalotis) fue un nuevo registro para la fauna rivereña, y ni el ratón de abazones sedosos (Perognathus flavus) ni la rata de abazones de Nelson (Chaetodipus nelsoni) fueron capturados durante el muestreo reciente. Diferencias en la estructura de estas comunidades son posiblemente causadas por los cambios en la vegetación rivereña la cual tiende a un tipo de bosque más cerrado o la recolonización después de inundaciones.