The origin of parachuting locomotion in gekkonid lizards (Reptilia: Gekkonidae)

Several recent studies have focused on the ability of the gekkonid Ptychozoon lionatum to parachute, utilizing its enlarged lateral body folds. Little attention has been paid, however, to the evolution of such behavious and here several aspects pertaining to the origin of parachuting are integrated. Behavioural shifts and morphological modifications are considered together and evaluated in the light of ecological information. It is apparent that certain behavioural shifts were the precursors of subsequent morphological changes. The structural design of the body folds is also considered in relation to parachuting behaviour and both the gross morphology and histology are shown to be significantly modified to permit effective parachuting. The absene of musculature in the lateral body flaps of geckos is confirmed and a model for the integration of the various factors involved in effective parachuting is presented. Here the importance of the "structure-function" and "habitat-behaviour" sets are emphasized together with their new interrelationships when a protoadaptation becomes functional.     

Mass and date at departure affect the survival of Ancient Murrelet Synthliboramphus antiquus chicks after leaving the colony

I compared the timing of colony departure and body mass of 53 Ancient Murrelet Synthliboramphus antiquus chicks that were retrapped as adults in Haida Gwaii, British Columbia, with those of 3992 chicks not retrapped. If the probability of recapture is a measure of survival, survival was related to both mass and date. Chicks that left the colony at 26 g or less had a lower chance of survival than heavier chicks, and those that left after the median date of departure survived better in some years than those that left earlier. The effect of date was not related to a seasonal change in departure mass because chick mass declined with departure date. I suggest that, because of heavy adult mortality during breeding, the timing of breeding in the Ancient Murrelet is based on a compromise between the optimum dates for chick and adult survival. This is in contrast to evidence from other, nonprecocial, seabirds.     

Population Estimation Techniques for Lekking Species

Abstract: With the decline of many lekking species, the need to develop a rigorous population estimation technique is critical for successful conservation and management. We employed mark—resight methods to estimate population size for 2 lekking species: greater sage-grouse (Centrocercus urophasianus) and Gunnison sage-grouse (Centrocercus minimus). We evaluated 2 different estimators: Bowden's estimator and the mixed logit-normal mark—resight model. We captured and marked 75 greater sage-grouse. We counted marked and unmarked birds as they attended 15 known leks. We used 36 and 37 marked Gunnison sage-grouse to estimate population size in 2003 and 2004, respectively. We observed marked and unmarked Gunnison sage-grouse daily as they attended 6 leks in 2003 and 3 leks in 2004. Based on our examination of the assumptions of each mark—resight estimator, relative to behavior and biology of these species, we concluded the mixed logit-normal mark—resight model is preferred. We recommend wildlife managers employ mark—resight approaches when statistically rigorous population estimates are required for management and conservation of lekking species.     

Spatial distribution and prediction of seed production by Eucalyptus microcarpa in a fragmented landscape

Woodlands worldwide have been greatly modified by clearing for agriculture, and their conservation and restoration requires understanding of tree recruitment processes. Seed production is one possible point of recruitment failure, and one that the spatial arrangement of trees may affect. We sampled 118 Eucalyptus microcarpa (Myrtaceae) trees to compare and analyse the determinants of seed production in this dominant tree of modified, fragmented temperate grassy woodlands, which extend over much of southeastern Australia. Fecundity was estimated as the seed crop measured on leaf mass and whole tree bases and was compared between categories of tree configuration. We also modelled fecundity using boosted regression trees, a new and flexible tool. Fecundity on a leaf mass basis was predominantly influenced by environmental factors (topographic ‘wetness’, slope, soil type), rather than by local tree density and configuration. Fewer seed per unit leaf mass were produced on flat and topographically wet sites, reflecting poor tolerance of waterlogging by E. microcarpa. By contrast, whole tree fecundity was little influenced by environmental factors. Local tree density and configuration did influence whole tree fecundity, which was high in solitary and woodland‐spaced trees and reduced under high local density. We found little evidence for reduced fecundity of E. microcarpa in solitary trees. This points to the importance of scattered trees as sources of seed for tree recruitment and for natural regeneration of landscape level tree cover. Considerable uncertainty remains in modelled seed supply, and may be reduced with sampling across multiple years and greater environmental and spatial domains.     

Fluctuations in circumpolar seabird populations linked to climate oscillations

We found that synchronous fluctuations of two congeneric seabird species across the entire Arctic and sub-Arctic regions were associated with changes in sea surface temperatures (SST) that were linked to two climate shifts, in 1977 and again in 1989. As the SST changes linked to climate shifts were congruent at the scale of ocean basins, fluctuations of these species occurred similarly at continental or basin scale. Changes in colony sizes were examined for a decade following climate shifts. The magnitude of the SST shift was more important than its direction in determining the subsequent rate of population change. Seabirds declined when the SST shift was large and increased when the shift was small, although the effect differed between the Arctic-breeding species and the more temperate-breeding congener. The Arctic species, Thick-billed Murre ( Uria lomvia ) increased most rapidly when SST warmed slightly, while the temperate species, Common Murre ( Uria aalge ) showed most rapid increase with moderate cooling. Both showed negative trends with large temperature shifts in either direction. This pattern was replicated during both climate oscillations. Negative population trends in seabirds presumably indicate the alteration of underlying food webs. Hence, similar widespread fluctuations in response to climate shifts are likely for other ecosystem components (marine mammals, fish, and invertebrates).     

Hyperparasitoid aggregation in response to variation in Aphidius ervi host density at three spatial scales

1. This article investigates the pattern of hyperparasitism of the host Aphidius ervi Haliday (Hymenoptera, Aphidiidae), a primary parasitoid of the pea aphid, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae) at three spatial scales.
2. In the laboratory, the hyperparasitoid Asaphes lucens (Provancher) (Hymenoptera: Pteromalidae) was introduced into cages containing sixteen alfalfa plants with varying numbers of A. ervi mummies (the stage susceptible to hyperparasitism). The pattern of hyperparasitism at the end of the 48-h trials showed no density-dependent hyperparasitoid aggregation, although there was strong density-independent hyperparasitoid aggregation.
3. In the field, the density of A. ervi mummies was manipulated in twelve 2 × 2-m plots containing 1309–1654 alfalfa stems. Variation in hyperparasitism among plots showed no density-dependent aggregation, although there was strong density-independent aggregation.
4. Finally, at the largest scale of the study, the distribution of hyperparasitism was sampled among twelve alfalfa fields within a 5 × 3-km area. At this scale there was both density-dependent and density-independent hyperparasitoid aggregation.
5. The natural variation in A. ervi mummy density is greatest at the larger scales of study. Therefore, density-dependent hyperparasitism occurs only when there is high natural variation in mummy density.