HOW BIG AND HOW CLOSE? HABITAT PATCH SIZE AND SPACING TO CONSERVE A THREATENED SPECIES

Abstract. We present results of a spatially explicit, individual‐based stochastic dispersal model (HexSim) to evaluate effects of size and spacing of patches of habitat of Northern Spotted Owls (NSO; Strix occidentalis caurina) in Pacific Northwest, USA, to help advise recovery planning efforts. We modeled 31 artificial landscape scenarios representing combinations of NSO habitat cluster size (range 4–49 NSO pairs per cluster) and edge‐to‐edge cluster spacing (range 7–101 km), and an all‐habitat landscape. We ran scenarios using empirical estimates of NSO dispersal dynamics and distances and stage class vital rates (representing current population declines) and under adult survival rates adjusted to achieve an initially stationary population. Results suggested that long‐term (100‐yr) habitat occupancy rates are significantly higher with habitat clusters supporting ≥25 NSO pairs and ≤15 km spacing, and with overall landscapes of ≥35–40% habitat. Although habitat provision is key to NSO recovery, no habitat configuration provided for long‐term population persistence when coupled with currently observed vital rates. Results also suggested a key role of floaters (unpaired, nonterritorial, dispersing owls) in recolonizing vacant habitat, and that the floater population segment becomes increasingly depleted with greater population declines. We suggest additional areas of modeling research on this and other threatened species.     

Transition State Thermodynamics of Lipid Bilayers Characterized by Differential Scanning Calorimetry

The laboratory experiment presented in this paper focuses on using differential scanning calorimetry to determine the calorimetric enthalpy and cooperativity of the gel to liquid crystalline phase transition in hydrated lipid bilayers as a function of cholesterol content. The procedure and analysis are appropriate for junior-and senior-level physics and biophysical chemistry courses in the undergraduate curriculum. The laboratory is used to emphasize the use of thermodynamic data to obtain information about structure-function relationships in biological systems. The experimental results are directly related to the authors ongoing research in lipid bilayer structure characterization and applications of hydrated lipid bilayers as model systems for the interpretation of MRI contrast. The laboratory is easily modified to study the effects of other conditions, such as degree of hydration, pH, and composition, on the thermodynamic behavior of lipid bilayers.