Sinks without borders: snowshoe hare dynamics in a complex landscape

A full understanding of population dynamics of wide-ranging animals should account for the effects that movement and habitat use have on individual contributions to population growth or decline. Quantifying the per-capita, habitat-specific contribution to population growth can clarify the value of different patch types, and help to differentiate population sources from population sinks. Snowshoe hares, Lepus americanus , routinely use various habitat types in the landscapes they inhabit in the contiguous US, where managing forests for high snowshoe hare density is a priority for conservation of Canada lynx, Lynx canadensis . We estimated density and demographic rates via mark–recapture live trapping and radio-telemetry within four forest stand structure (FSS) types at three study areas within heterogeneous managed forests in western Montana. We found support for known fate survival models with time-varying individual covariates representing the proportion of locations in each of the FSS types, with survival rates decreasing as use of open young and open mature FSS types increased. The per-capita contribution to overall population growth increased with use of the dense mature or dense young FSS types and decreased with use of the open young or open mature FSS types, and relatively high levels of immigration appear to be necessary to sustain hares in the open FSS types. Our results support a conceptual model for snowshoe hares in the southern range in which sink habitats (open areas) prevent the buildup of high hare densities. More broadly, we use this system to develop a novel approach to quantify demographic sources and sinks for animals making routine movements through complex fragmented landscapes.     

Catecholamine content of the carotid body in cats ventilated with 8 - 40% oxygen.

The content of catecholamines in the carotid body varies directly with inspired oxygen concentration in the range between 8 and 40% oxygen. The decrease in content during hypoxia is mediated mainly through an efferent neural pathway in the carotid sinus nerve.     

Bursicon-induced adenyl cyclase activity in the haemocytes of the American cockroach

Partially purified preparations of bursicon were injected, between ecdyses, into American cockroaches (Periplaneta americana) held at 4°C. After short periods of time, the haemocytes were removed and found to contain appreciable amounts of cyclic adenosine 5′-monophosphate (cAMP). Identical experiments using animals reared at 23°C did not result in the accumulation of cAMP. These and additional data suggest that phosphodiesterase is not active during the initial stages of bursicon-stimulated adenyl cyclase.Incubation of haemocyte soluble proteins in the presence of [³H]cAMP, followed by molecular sieve chromatography on P-60 polyacrylamide gel, shows the binding of cAMP to large molecular weight proteins. Similar experiments, but with phosphodiesterase inhibition revealed a reduced level of radioactive bound protein. From these studies one can assume that the haemocytes contain a soluble cAMP-dependent protein kinase.If either [¹⁴C]-leucine or [¹⁴C]-tyrosine is incubated with whole blood taken from animals between ecdyses, little or no uptake by the haemocytes can be seen. Identical studies, but with the addition of cAMP, results in a dramatic enhancement of amino acid uptake. It appears that bursicon stimulates blood-cell adenyl cyclase, which in turn produces cAMP. The cAMP subsequently activates a specific protein kinase that phosphorylates potential membrane proteins. The membrane phosphoprotein may be instrumental in the enhanced uptake of amino acids.     

Midgut epithelium of the American cockroach: Control of lumen volume by substances from the terminal abdominal ganglion

Three substances partially purified from extracts of the terminal abdominal ganglion influence the volume of fluid in the lumen of the midgut. Column chromatography on P-30 polyacrylamide gel indicates that one component may have a molecular weight greater than 30,000. This component increases secretion of fluid into the lumen as does a low molecular weight compound of unknown composition.