Population Dynamics of Breeding Mallards in the Great Lakes States

Abstract: Mallard (Anas platyrhynchos) populations in the United States portion of the Great Lakes region increased through the 1990s but have since declined. To promote sustainable growth of this population, managers need to understand how perturbation of vital rates will affect annual population growth rate (Λ). We developed a stage-based model representing the female mallard population in the Great Lakes using vital rates generated from a landscape-level study documenting reproductive parameters from 2001 to 2003. We conducted perturbation analyses (i.e., sensitivity analyses) to identify vital rates that most influence Λ and variance decomposition analyses to determine the proportion of variation in Λ explained by variation in each vital rate. Perturbation analyses indicated that Λ was most sensitive to changes in nonbreeding survival, duckling survival, and nest success. Therefore, changes in these vital rates would be expected to result in the greatest ΔΛ. Process variation in breeding season parameters accounted for 63% of variation in Λ. Breeding season parameters explaining the most variation were duckling survival (32%) and nest success (16%). Survival of adult females outside the breeding season accounted for 36% of variation in Λ. Harvest derivation, high harvest, and high sensitivity of Λ to nonbreeding survival for Great Lakes female mallards suggests there is a strong potential for managing the Great Lakes mallard population via harvest management. Because Λ was highly sensitive to changes in duckling survival, we suggest programs that emphasize wetland protection, enhancement, and restoration as a management strategy to improve population growth for breeding mallards.     

Mobility and metapopulation structure of Geocrinia alba and Geocrinia vitellina,two endangered frog species from southwestern Australia

Abstract Dispersal rates can have an important impact on many population processes. Dispersal can lead to population regulation and regional stability in the face of local instability through the formation of a metapopulation. This may be particularly true for frogs because they often have patchy distributions. In this paper I investigate dispersal by male Geocrinia alba and Geocrinia vitellina, using a mark-recapture study. Pit traps were used to determine whether frogs move out of their breeding habitat. I found that both species were very philopatric. Between the 1993 and 1994 breeding seasons, 76–86% of individuals were displaced less than 10m and 90–97% were displaced less than 20m. Dispersal was even lower within each breeding season, with 92–95% of individuals being displaced less than 5 m. Pit trapping indicated that some individuals of both species move out of the swamps in late autumn and return at the beginning of the breeding season, in late winter and early spring. Therefore, although displacement may be very restricted, the frogs are likely to move greater distances. The extreme breeding-site philopatry exhibited by G. alba and G. vitellina suggests that movement between disjunct populations is unlikely and that populations in continuous habitat may be relatively isolated from one another by distance alone. This is consistent with previous predictions based on genetic studies, which suggested there was very little migration between populations. These data support the contention that neither species is likely to exist as a metapopulation because recolonization of vacant habitat is improbable.     

Cellular Aspects of the Control of Physiological Color Changes in Amphibians

SYNOPSIS. The present paper is concerned mainly with the melanin-dispersingeffect of melanocyte-stimulating hormones (MSH's) on the skinmelanophores of amphibians. In addition, some of the more recentevidence for the unihumoral theory of the control of color changeis reviewed. The mechanism of dispersion of melanin is stillunknown, but evidence is accumulating that the action of MSHmay be mediated by an increase in the melanophoric content ofadenosine 3', 5'-monophosphate (cyclic AMP). For example, cyclicAMP has a specific, reversible melanin-dispersing effect onthe melanophores of the isolated skin of R. pipiens and Xenopuslaevis. It also has a reversible "melanophore—expanding"effect on the tissue—cultured embryonic melanophores ofthe spotted salamander, Ambystoma maculatum. The effect of cyclicAMP on melanophores of R. pipiens does not require sodium butis inhibited by hypertonicity. Finally, new evidence is presented that confirms that the melanin-dispersingeffect of catecholamines on melanophores of X. laevis is mediatedby beta adrenergic receptors,because it is blocked by the highlyspecific ß—blocking agent, propranolol. On theother hand, the melanin-aggregating effect of catecholamineson amphibian melanophores appears to be mediated by alpha adrenergicreceptors. There is even a possibility that the effects of catecholaminesare also mediated through a control of cyclic AMP levels inmelanophores, with beta adrenergic stimulation producing anincrease in cyclic AMP levels, followed by dispersion of melanin,and alpha adrenergic stimulation producing a decrease in cyclicAMP levels, followed by aggregation of melanin.     

THE ADVANTAGES OF A PLATINUM TUBE DROPPING PIPETTE FOR MAKING COLONY COUNTS

SUMMARY: For routine purposes where a large number of tests is involved the dropping pipette technique has many advantages over other methods of determining the colony count. However, glass pipettes are fragile and much time and labour have to be used in making and calibrating replacements. A robust platinum tube dropping pipette has been found very satisfactory. No difficulty was experienced in obtaining complete sterility of the pipettes in the technique described, and reproducibility of drop size was good.     

Seasonal changes in primary and secondary inoculum during epidemics of leaf blotch (Rhynchosporium secalis) on winter barley

Seasonal changes in numbers of conidia of Rhynchosporium secalis on debris from previous barley crops infected with leaf blotch (primary inoculum) were monitored in 1985–86 and 1986–87. In 1986–87, changes in numbers of conidia on leaves of plants in the new winter barley crop (secondary inoculum) were also recorded. The greatest increases in production of primary inoculum were in early spring after rain, when temperatures were increasing after periods of sub-zero temperatures when there was little conidial production. Subsequently, more conidia were recovered from this debris after cycles of drying and rewetting than when it remained wet. After January 1987, amounts of secondary inoculum produced on the crop were much greater than amounts of primary inoculum on debris. Most spores were produced on the basal leaves and more spores were present on the September-sown than on the November-sown crop. Thus, while primary inoculum was a source of disease when plants were emerging, secondary inoculum on basal leaves was the main source of disease at stem extension, especially on early-sown crops.