Kerry L. Griffis-Kyle

Small isolated aspen stands enrich bird communities in southwestern ponderosa pine forests

Small aspen stands are disappearing from the landscape in the Southwest, so it is important to understand their contribution to the avian community. We sampled birds in 53 small, isolated aspen stands and 53 paired plots within the ponderosa pine forest in northern Arizona, during the 1996 and 1997 breeding seasons. Bird species richness and abundance were higher in aspen than in pine. However, bird species richness and abundance did not vary with size of the aspen patch or isolation index. In addition, direct ordination of species distributions with habitat factors suggested no distinct avian communities. This suggests that aspen stands do not harbor separate populations, but rather are locations where the regional avifauna reaches high local density and richness and may be crucial to birds in years of resource scarcity. Thus it is important for avian conservation to maintain many aspen stands across the landscape, encompassing a diversity of vegetation structure and composition.

Ontogenic delays in effects of nitrite exposure on tiger salamanders (Ambystoma tigrinum tigrinum) and wood frogs (Rana sylvatica).

Under certain conditions, nitrite can be present in freshwater systems in quantities that are toxic to the fauna. I exposed wood frog (Rana sylvatica) and eastern tiger salamander (Ambystoma tigrinum tigrinum) embryos and young tadpoles and larvae to elevated concentrations of nitrite in chronic toxicity tests: 0, 0.3, 0.6, 1.2, 2.1, 4.6, and 6.1 mg/L NO2-N, exposing individuals as both embryos and larvae. Nitrite caused significant declines in wood frog hatching success (3.4 mg/L NO2-N, wood frog), and lower concentrations caused significant mortality during the early larval stages (4.6 mg/L NO2-N, salamander; 0.5 mg/L NO2-N, wood frog). Later tests exposing individuals to nitrite only after hatching showed that both wood frog and tiger salamander vulnerability to nitrite declined shortly after hatching. Hence, examining a single life-history stage, especially later in development, may miss critical toxic effects on organisms, causing the researcher potentially to underestimate seriously the ecological consequences of nitrite exposure.

Migratory Strategy and Seasonal Patterns of Bird Diversity in Relation to Forest Habitat

Abstract Aspen stands and riparian areas are important to breeding birds in the southwestern U.S. because they provide resources such as food and shelter. We investigated how this importance varies throughout the year for both resident and migratory birds. We sampled birds in 96 sites, half in small isolated aspen stands and half in the ponderosa pine forest in northern Arizona during the summer of 1996, and a subset of those plots during fall of 1996 and the spring of 1997. Bird species richness and abundance varied seasonally. During the summer there were more birds and more bird species in aspen stands. This relationship appears to be driven by an affiliation between Neotropical migrants and aspen trees. During fall, residents were associated with riparian areas. We demonstrate the importance of small inclusions of aspen to Neotropical migrants in the Southwest during the breeding season and we show that preference for habitat types among migratory groups can vary seasonally.

Anuran Habitat Associations in the Northern Chihuahuan Desert, USA

Abstract Understanding amphibian habitat associations allows us to assess the impacts of environmental change on amphibian populations. We studied the habitat associations of five anurans in the Chihuahuan Desert of southern New Mexico, USA. We used amphibian call surveys at 36 ephemeral water bodies and recorded an index of abundance for each species. We used GIS to identify vegetation communities (e.g., creosote bush, grassland, mesquite) within a buffer zone around each water site. We used ordinal logistic regression, Akaikes information criterion (AICc), and canonical correspondence analysis to elucidate relationships between an index of anuran abundance and habitat variables. Creosote bush, mesquite, and grasses dominate the landscape in our study region. We detected Anaxyrus debilis (Green Toad) and Spea multiplicata (New Mexico Spadefoot Toad) most frequently (>70% of water bodies observed). Anaxyrus cognatus (Great Plains Toad), Scaphiopus couchii (Couchs Spadefoot Toad), and Spea bombifrons (Plains Spadefoot Toad) were detected at about half of water bodies studied. Anaxyrus cognatus, Spea bombifrons, and Sp. multiplicata tended to co-occur at breeding sites. Anaxyrus cognatus and Sp. bombifrons were more common in mesquite habitat. Succulent desert scrub, though not common, seemed to affect Sc. couchii positively and A. debilis negatively. Spea multiplicata was more generalistic and did not show strong habitat associations. We did not find evidence that shrub encroachment has had negative impacts on the amphibian community in our study system and may even have had positive effects on anurans, especially A. cognatus and Sp. bombifrons.

Use of Breeding Sites by Arid-Land Toads in Rangelands: Landscape-Level Factors

Abstract We examined spatial extent of habitat that anaxyrids responded to in an arid environment. We used surveys of vocalizations and searches to identify toads after rainfall events to examine whether the spatial arrangement and proximity of earthen tanks could influence breeding populations of Anaxyrus cognatus and A. debilis. These species responded to the landscape complement of breeding sites inside a buffer of 5 km, a much larger distance than most studies have addressed.

Low Genetic Differentiation among Populations of the Great Plains Toad (Bufo cognatus) in Southern New Mexico

Abstract We examined the genetic population structure for the Great Plains Toad (Bufo cognatus) in the Chihuahuan Desert of southern New Mexico in order to discern at what spatial scale genetic differentiation is apparent. In addition, we tested whether habitats in the Chihuahuan Desert of southern New Mexico differed in their resistance to gene flow in B. cognatus. We used microsatellites to estimate genetic differentiation in populations that varied in distance from 1 to 60 km. Of 120 pairwise tests of genetic differentiation, 44 were significant. However, differentiation was low between all sites (FST  =  0.0–0.087), almost all of the genetic variation being within populations (96.3%). Compared to published studies of other anuran species, populations of B. cognatus in southern New Mexico are among the most genetically homogenous anuran species. Significant isolation by distance did occur over all populations despite the genetic similarity, suggesting that differentiation does occur at a broader scale. In addition, several landscape-based models of gene flow were produced and tested against the allelic data. A community model assigned each plant community a different level of resistance to gene flow. This model was not found to describe the estimated genetic variation between populations better than simple Euclidean distance. However, the river model, which assigned low resistance to the aquatic habitats including the Rio Grande, described the estimated genetic variation better than Euclidean distance, suggesting that the Rio Grande, and potentially other rivers throughout the toads range, may act as a route of dispersal for B. cognatus, reducing genetic differentiation among distant populations.

Mosquitoes of North America with emphasis in the midwestern United States: long-term occurrence patterns

Abstract Mosquitoes are ecologically and economically important invertebrates that transmit numerous diseases and are an integral part of the food web in many terrestrial and aquatic ecosystems. Despite their importance, there have been no central repositories for occurrence or abundance records of mosquitoes in the United States. To enable research dependent on the geographic distribution and abundance of mosquito species, we built a database of occurrence records collected by many individuals and agencies, primarily in the United States and with emphasis on unpublished data in the Midwest region. This resource is invaluable to researchers studying mosquito ecology, disease vectors and pathways, and insect pests. The database contains 542 144 occurrence records, and each record includes information on sex, life stage, sampling method, presence/absence or abundance, and date and location of sampling. The accessibility of this resource will directly impact management and planning for mosquito-borne disease...