On the black cotton soils of the Laikipia ecosystem in Kenya, two swollen-thorn acacia species support nine ant species, four of which are apparently obligate plant-ants. Among the ants, there are five species of Crematogaster, two species of Camponotus, and one each of Tetraponera and Lepisota. Acacia drepanolobium is host to four ant species that are both common and mutually exclusive. These four ant species, and an additional non-exclusive ant species, tend to occur on trees of different sizes, implying a succession of ant occupants. Nonetheless, all four exclusive species occur in substantial proportions on trees of intermediate size. There is direct evidence that an early successional ant species (Tetraponera penzigi) is actively evicted by two late successional ant species in the genus Crematogaster. There was also some evidence of height differentiation among ant species resident on A. seyal. Different acacia-ant species had different direct effects on A. drepanolobium. Extrafloral nectaries were eaten and destroyed only on trees inhabited by Tetraponera. Axillary shoots were eaten only on trees inhabited by C. nigriceps (potentially another early successional ant). This was associated with more new terminal shoots and healthier leaves than other trees, but also the virtual elimination of flowering and fruiting. Different resident acacia-ant species also had characteristic relationships with other insects. Among the four mutually exclusive ant species, only Crematogaster sjostedti was associated with two species of Camponotus, at least one of which (C. rufoglaucus) appears to be a foraging non-resident. A. drepanolobium trees occupied by C. sjostedti were also far more heavily infested with leaf galls than were trees occupied by other ant species. A. drepanolobium trees occupied by C. mimosae and C. sjostedti uniquely had tended adult scale insects. This diversity of ant inhabitants, and their strikingly different relationships with their hosts and other insect species, are examples of coexisting diversity on an apparently uniform resource.
We researched the environmental attributes (n = 28) associated with elk(n = 50) summer range (1 May‐30 Sep) in the central Black Hills of South Dakota, USA, during 1998–2001. We defined high‐use areas or centers of activity as landscapes underlying large concentrations of elk locations resulting from the shared fidelity of independently moving animals to specific regions on summer range. We divided the study area into 3‐km grid cells to represent the distance elk travel in a 24‐hour period. We computed mean elevation and slope, proportion and configuration of overstory canopy cover, proportion and configuration of dominant vegetation type, estimated biomass, road density, traffic rate, and amount of habitat not dissected by improved surface roads for each cell. We used a combination of multiple stepwise regression and likelihood ratio tests to develop spatially adjusted models with total number of elk locations per cell as the dependent variable. Environmental attributes varied in their significance based on their availability to different elk subpopulations. Collectively, the number of elk locations was positively associated (model r2 = 0.50, P < 0.001) with elevation, proportion of non‐road‐dissected habitat, shape complexity of meadows, proportion of forest stands with ≤40% overstory canopy cover, and proportion of aspen (Populus tremuloides). Elk were responsive to a landscape structure emphasizing forage potential, and their selection was based on the composition and pattern of both biotic and abiotic variables. Defining the characteristics of high‐use areas allows management to manipulate landscapes so as to contain more of the habitats preferred by elk.
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