Restricted cross-scale habitat selection by American beavers.

Animal habitat selection, among other ecological phenomena, is spatially scale dependent. Habitat selection by American beavers Castor canadensis (hereafter, beaver) has been studied at singular spatial scales, but to date no research addresses multi-scale selection. Our objectives were to determine if beaver habitat selection was specialized to semiaquatic habitats and if variables explaining habitat selection are consistent between landscape and fine spatial scales. We built maximum entropy (MaxEnt) models to relate landscape-scale presence-only data to landscape variables, and used generalized linear mixed models to evaluate fine spatial scale habitat selection using global positioning system (GPS) relocation data. Explanatory variables between the landscape and fine spatial scale were compared for consistency. Our findings suggested that beaver habitat selection at coarse (study area) and fine (within home range) scales was congruent, and was influenced by increasing amounts of woody wetland edge density and shrub edge density, and decreasing amounts of open water edge density. Habitat suitability at the landscape scale also increased with decreasing amounts of grass frequency. As territorial, central-place foragers, beavers likely trade-off open water edge density (i.e., smaller non-forested wetlands or lodges closer to banks) for defense and shorter distances to forage and obtain construction material. Woody plants along edges and expanses of open water for predator avoidance may limit beaver fitness and subsequently determine beaver habitat selection.

Influence of spatial resolution on assessing channelization impacts on fish and macroinvertebrate communities in a warmwater stream in the southeastern United States.

The choice of spatial and temporal scale used in environmental assessments may influence the observed results. One method of assessing the impact of stream habitat alterations involves the comparison of response variables among treatment categories (i.e., impacted and unimpacted sites). The influence of spatial resolution on patterns of response variables among treatment categories in assessments of stream channelization and other types of habitat alterations has not been evaluated. We examined how patterns of 10 community response variables among channel types and our interpretations of channelization impacts on fish and macroinvertebrate communities differed among three spatial resolutions in a warmwater stream in Mississippi and Alabama. Four fish and three macroinvertebrate community response variables exhibited different patterns among channel types at different spatial resolutions. Our interpretations of the impacts of channelization on fish and macroinvertebrate communities differed among spatial resolutions. Channelization had a negative influence on fish communities either with or without evidence of potential community recovery in one channel type. Channelization impacts on macroinvertebrate communities ranged from a negative influence to no effect. Our results suggest that spatial resolution can influence the observed results and interpretations derived from assessments of stream habitat alterations.

A simple method to estimate spatial complexity in aquatic plants

Neste trabalho foi medida a complexidade espacial que contribui para a estrutura de habitat proporcionada por 8 espécies de plantas aquáticas coletadas em lagoas da planície de inundação do alto rio Paraná. As espécies analisadas foram Cabomba furcata Schult. and Schult.f. Eichhornia azurea (Sw.) Kunth (caules e raízes), Eichhornia crassipes (Mart.) Solms, Egeria najas Planchon, Heteranthera cf. zosterifolia, Potamogeton cf pusillus, Utricularia foliosa L. e Nymphaea amazonum Mart. and Zucc. A complexidade dos segmentos terminais de 0,5 m foi medida em laboratório. Fotografias digitais desses segmentos foram feitas e análises dos eixos verticais e horizontais foram realizadas ao longo de transecções superpostas às imagens, em computador. A freqüência e o comprimento dos insterstícios ao longo de ambos os eixos foram tomados para determinar o índice de complexidade espacial. A freqüência e o comprimento médios dos interstícios foram significativamente diferentes entre as espécies de plantas. A complexidade espacial também variou entre as espécies (F = 17,30; p < 0,0001), com as raízes de E. azurea e U. foliosa exibindo os maiores valores e os caules de E. azurea e N. amazonum os menores. Estes valores da complexidade espacial, únicos para cada espécie, sugerem que as plantas aquáticas possuem uma contribuição diferenciada para a heterogeneidade de habitats dos ambientes aquáticos do alto rio Paraná.