The effects of temperature on germination and early growth of three plant species indigenous to Central Australia

The temperature responses of the perennial grass Eragrostis eriopoda Benth., an all-season annual grass (Enneapogon polyphyllus Domin.) and a cool-season annual forb (Lepidium muelleri-ferdinandi Thell.) were studied in two experiments, one during germination and the other during the establishment phase. In the first experiment, extreme differences in the response of germination to temperature occurred between species. The optimum was 42°C for Eragrostis and 15 to 21° C for Enneapogon and Lepidium although Enneapogon tolerated higher temperatures than did Lepidium. The effect of temperature on speed of germination is discussed. In the second experiment, seedlings were assigned to six day/night temperature regimes ranging from 24/16 C to 45/31 C for three weeks in a phytotron. Both grasses responded positively to temperatures tip to 30/22°C with little further change up to 45/37° C, while Lepidium died at temperatures greater than 30/22° C. The experimentally determined response to temperature reflected field observations of seasonal establishment patterns for each species. The ecological significance of the results is discussed.     

Observations on the development and maintenance of the deep sea barnacle,Octolasmis aymonini geryonophila (Pilsbry)

Thirty-two pedunculate barnacles, O. a. geryonophila, were maintained in culture for a period of 2 yr in the laboratory. These barnacles were obtained from the pleopods and mouth parts of the giant marine isopod, Bathynomus giganteus, which had been collected, at a depth of 200 fathoms, in the Gulf of Mexico.

The carina, scutum, mandible and maxilla of adult barnacles were typical of deep water species. However, the tergum and labrum were intermediate between those of shallow and deep water species.

Adults 3.1–4.1 mm in length were cultured in sea water (15–19°C), and fed on benthic copepods such as Tisbe furcata and Laophonte sp. Three broods of nauplii from 8 barnacles were obtained in 2 yr. Larvae were reared on plankton collected from Coney Island waters in which nauplii reached Stage IV in 10–14 days at 16°C. Isochrysis galbana and Thalassiosira pseudonana individually or in combination maintained nauplii to Stage IV, but with very high mortality. The lack of spines on the carapace edge of the nauplii distinguishes this deep water species from the shallow water form, O. mulleri.     

Submerged macrophytes, zooplankton and the predominance of low- over high-chlorophyll states in western boreal, shallow-water wetlands

1. Shallow‐water (<2 m deep) wetlands in northern Alberta's western boreal forest tend to have either extremely high‐chlorophyll, pea‐green water or water that is low in chlorophyll and clear. The relative importance of top‐down processes (e.g. zooplankton grazing) compared with bottom‐up processes (e.g. nutrient limitation) for regulating the existence of these alternate states has yet to be explicitly investigated in these poorly studied waterbodies. 2. To assess the relationship between chemical and biological factors and the predominance of low‐chlorophyll over high‐chlorophyll states, a survey of 24 shallow‐water wetlands in northern Alberta was conducted over the summers of 2001 and 2002. 3. In wetlands without fish, statistical analysis indicated that high‐ and low‐chlorophyll sites could be differentiated with 82% accuracy based solely on whether submerged aquatic vegetation (SAV) coverage was greater or less than 25%. Further, high‐SAV lakes with zooplankton communities dominated by large cladocerans were clear 96% of the time. 4. In the few wetlands that supported stickleback populations, large cladocerans were absent. However, the development of zooplankton communities dominated by small cladocera (Bosmina) with calanoid copepods in fish‐containing wetlands corresponded with a shift from high‐ to low‐chlorophyll states. 5. Results suggest that in fishless wetlands high‐SAV coverage and grazing by large, SAV‐associated cladocerans promotes low‐chlorophyll states. Results also suggest that suppression of macroinvertebrate predators by sticklebacks allowing Bosmina to flourish may also promote low‐chlorophyll, clear‐water conditions.     

Rio Grande Wild Turkey Habitat Selection in the Southern Great Plains

ABSTRACT We recorded telemetry locations from 1,129 radiotagged turkeys (Meleagris gallopavo intermedia) on 4 study areas in the Texas Panhandle and southwestern Kansas, USA, from 2000 to 2004. Analyses of telemetry locations indicated both sexes selected riparian vegetative zones. Females did not select grazed or nongrazed pastures for daily movements. However, females did select nongrazed pastures for nest sites on 2 study areas and males selected for grazed pastures at one study area during the breeding season. We compared nest sites (n = 351) to random sites using logistic regression, which indicated height of visual obstruction, percent canopy cover, and percent bare ground provided the highest predictive power (P ≤ 0.003) for characteristics describing nest-site selection. Nest-site vegetative characteristics between vegetative zones differed primarily in composition: upland zone nest sites had more (P ≤ 0.001) shrubs and riparian zone nest sites had more (P ≤ 0.001) grass. There were no differences in measured nest site vegetative characteristics between pasture types, but there were differences between available nesting cover in grazed and nongrazed pastures. Random plots in grazed pastures had less grass cover (P ≤ 0.001) and more bare ground (P = 0.002). Because of cattle impacts on average grass height and availability, grazing would likely have the highest impact on nesting in riparian zones due to turkey use of grass as nesting cover. An appropriate grazing plan to promote Rio Grande turkey nesting habitat would include grazing upland zones in the spring, when it likely has little impact on nesting-site selection, and grazing riparian zones following breeding season completion. Grazing at light to moderate intensities with periods of rest did not affect male turkey pasture use and may have continued to maintain open areas used by male turkeys for displaying purposes.