Gary D. Schnell

Effects of agriculture on habitat complexity in a prairie-forest ecotone in the Southern Great Plains of North America

Abstract Ecotones are transition zones that may be particularly sensitive to both natural and human-related disturbances to the environment. Agricultural development in the southern Great Plains of North America has resulted in marked changes in habitats and in the configurations of those habitats. Based on panchromatic National High Altitude Photography (NHAP), the effects of such development on spatial extent, relative abundance, and habitat-patch complexity for 15 land-cover types were evaluated by contrasting landscape-level habitat characteristics of a managed-native landscape (Fort Sill Military Reservation in southwestern Oklahoma, USA) with those of the adjacent landscape, where agricultural uses were the most prevalent. The managed-native landscape was predominately grassland (62.2%), with most being mixed grassland (43.4%), while the surrounding agriculture landscape was dominated by rangeland (50.7%) and cropland (13.6%). The mean area and perimeter of grassland patches in the managed-native area were greater than in the agriculture area, while values of these measures for cropland and rangeland patches were greater in the agriculture area. Mean patch shape (corrected perimeter/area) was highest for bottomland-forest, riparian, and cross-timbers habitats, reflecting the fact that these habitats typically are elongated in shape. Mean patch shapes of mesquite-savanna, bottomland-forest, and riparian patches were significantly lower in the agriculture area, a result primarily due to the straightening of edges of patches of these habitats when croplands were developed adjacent to them. With two relatively large reservoirs being present in the agriculture area, mean patch shape for water also was significantly lower than that in the managed-native landscape. Overall, fractal dimension—a measure of shape complexity of the perimeter of habitat patches—was significantly lower (based on Monte Carlo simulation) for the agriculture area than the managed-native area, mirroring the fact that habitat edges in the cropland-dominated area were less complex for many of the land-cover types. For specific land-cover types, cropland had a significantly higher fractal dimension in the agriculture area than the managed-native area, while the opposite was true for water, mixed grass, distributed areas, riparian, and bottomland forest. These results indicate that habitat complexity in the prairie-forest ecotone is reduced by agricultural development, which potentially could have deleterious effects on native plants and animals.

NEW SPECIES OF STURNIRA (CHIROPTERA: PHYLLOSTOMIDAE) FROM NORTHERN SOUTH AMERICA

Abstract Yellow-shouldered bats (genus Sturnira Gray, 1842), found throughout Latin America, are not well understood taxonomically. Four specimens of Sturnira from Bolivia and Venezuela possess dental characteristics differing from those of currently known species, leading us to regard them as representing a new species. We describe external, dental, and cranial characteristics and conduct a multivariate comparison using 29 morphometric characters for 44 male specimens of Sturnira erythromos, S. ludovici, S. hondurensis, and the new species. In a principal components analysis, most of the variation was summarized on component I (78.5% of total character variance), a general size vector. A multiple-comparisons test of component I projections showed all differences among species pairs to be highly significant, except that between S. ludovici and S. hondurensis. For the 29 individual characters, the new species was statistically different from S. erythromos in 21, S. ludovici in 13, and S. hondurensis in 14. The new species has a unique combination of dental characteristics, including bicuspid upper incisors, trilobed lower incisors, and smooth 1st and 2nd lower molars.

The Elements of Graphing Data.

The power of graphs, improving graphs, and history. Principles of graph construction. Graphical methods. Graphical perception.