The successional status of Cupressus arizonica

Several investigations (size-class analysis, age-determination inquiries, and germination tests) suggest that Cupressus arizonica of southeastern Arizona is a pioneer species. The tree requires disturbance to remove or reduce soil litter, which otherwise inhibits the reproduction of the species. Reduction of light intensity caused by canopy closure appears to be less important than litter accumulation in restricting C. arizonica reproduction. Following disturbance, successful establishment of seedlings may occur over an extended period (50 to 100 years), as litter gradually accumulates. The absence of C. arizonica seedlings in present populations suggest that fire suppression policies on federal lands where C. arizonica occurs have altered fire frequency, and consequently have fostered a short-term reduction in C. arizonica establishment. Only in floodplain environments, where flooding disturbs the soil surface, has much reproduction occurred in recent years. The long-term population pattern of C. arizonica appears stable, due to the great longevity of the species.     

Diets of sympatric Lahontan cutthroat trout and nonnative brook trout: implications for species interactions

Nonnative brook trout ( Salvelinus fontinalis ) have been implicated in declines of stream-living Lahontan cutthroat trout ( Oncorhynchus clarki henshawi ), a threatened trout endemic to the Lahontan Basin of northeastern California, southeastern Oregon, and northern Nevada. Brook trout may displace Lahontan cutthroat trout through 2 mechanisms: interspecific predation and competition for food. To evaluate the evidence for these alternatives, we examined stomach contents of 30 trout of each species captured in the North Fork Humboldt River, northeastern Nevada, to compare number, size, and taxonomic composition of prey. Taxonomic dietary overlap was high (81.4%) between brook and Lahontan cutthroat trout. Both species were nonselective in their feeding habits. Lahontan cutthroat trout consumed over 2.5 times as many prey on average, but brook trout consumed significantly larger prey. No trout of either species occurred in fish diets. Only a single fish, a Paiute sculpin ( Cottus beldingi ), was found in stomachs, and the majority (>90%) of prey consisted of insect taxa. Size and number of prey consumed were positively related to fish size for Lahontan cutthroat trout, but not for brook trout. These results do not provide compelling evidence to suggest feeding by Lahontan cutthroat trout is limited by presence of large numbers of brook trout in the North Fork Humboldt River. However, fundamental differences in each species utilization of food in this system indicate that a better understanding of observed differences may help to explain the variable success of brook trout invasions across stream habitats in the Lahontan Basin and their potential effects on Lahontan cutthroat trout.     

Disturbance of lekking Lesser Prairie-Chickens ( Tympanuchus pallidicinctus ) by Ring-necked Pheasants ( Phasianus colchicus )

Lesser Prairie-Chicken ( Tympanuchus pallidicinctus ) populations have experienced dramatic rangewide declines (up to 92%) since settlement of the Great Plains. This decline has been attributed to changes in land-use practices, such as conversion of native rangelands to intensive agriculture and increased grazing pressure. These changes may increase the impact of interspecific competition on populations. We documented disturbance of lekking Lesser Prairie-Chickens by Ring-necked Pheasants ( Phasianus colchicus ). Future management and research should take into account possible impacts to Lesser Prairie-Chickens during the breeding season.