RADULAR PRODUCTION RATES IN TWO SPECIES OF LACUNA TURTON (GASTROPODA: LITTORINIDAE)

The molluscan radula is a dynamic organ, both in terms of itsuse and production. New rows of teeth are constantly producedat the posterior end of the radula, while older, worn teethare shed anteriorly, producing a dynamic equilibrium. We useda cold-shock to mark the radular ribbon and measure tooth rowproduction rates in two gastropod species, Lacuna vincta (Montagu)and L. vanegata Carpenter. We found that the average tooth rowproduction rate at 10–11°C did not differ betweenthese two species, and was 2.94 (SE = 0.002) rows per day forLacuna vincta and 2.97 (SE = 0 002) for L. vanegata Inter-individualvariability in production rate was very low, and was correlatedwith shell length, smaller individuals had slightly higher productionrates. The total length of the radular nbbon varied greatlyamong individuals, ranging from 47 to 94 (2.57 to 5.68 mm) rowsin L vincta and 53 to 99 rows (2.80 to 7.14 mm) in L vanegata,and was only somewhat correlated with the length of the shelLThis great variability will result in large differences amongindividuals in the time it takes to replace the radula totally,from 14.96 to 35.44 days in L vincta and from 17 43 to 39 69days in L. vanegata. (Received 1 September 1995; accepted 20 November 1995)     

Satellite tracking of the winter migration of Magellanic Penguins Spheniscus magellanicus breeding in the Falkland Islands

Magellanic penguin populations in the Falkland Islands may have decreased over the past decade. The post-breeding migration may be the period in which the birds are most vulnerable. To investigate this we equipped ten Magellanic Penguins after their moult at Seal Bay (51̀38'S, 58̀03'W), East Falkland, with satellite transmitters. The movements of the penguins were tracked for between 15 and 99 days until transmission ceased. All birds initially migrated to the northwest. However, four birds entered Argentinean coastal waters, then headed northeast following the coastline, The other penguins remained offshore, but also changed to a northeasterly course. Two birds migrated beyond 36̀S with a maximum distance to the colony of more than 1800 km, while the minimum distance travelled was up to 2700 km. Initially, the birds migrated quickly but their speed was reduced and became more variable as time progressed. A high concentration of positional fixes, associated with low travelling speeds, indicated at least four different areas where birds were assumed to forage efficiently. The relevance of these areas is discussed with respect to the diet of Magellanic Penguins and possible interactions with human activities.     

Replicability of physicochemistry and macroinvertebrate assemblages in stream mesocosms: implications for experimental research

1. The replicability of mesocosms is assessed in a case study of artificial streams (4 m²) flanking a lowland chalk river in southern U.K. Among‐mesocosm comparisons of physicochemistry and macroinvertebrate assemblage composition (in drift and benthos) were made during a 2‐year survey of 12 outdoor once‐through linear channels. 2. Mesocosm physicochemistry was highly replicable, with statistically significant congruence in temporal variation across the mesocosm series, low spatial variation and no significant blocking or positional effects arising from mesocosm layout. Parallel physicochemistry was attributed to the outdoor stream‐side location and short water residence times. 3. Mesocosms were colonized by 127 macroinvertebrate taxa from 15 taxonomic orders. Both benthic and drifting assemblages were comparable among mesocosms, with no significant effect of mesocosm layout. Small differences in taxonomic composition were, however, evident among particular mesocosms, with higher (e.g. Tinodes, Limnius and Elmis) or lower (e.g. Pisidium and Valvata) abundances observed for a minority (5%) of taxa. We conclude that large (4 m²) outdoor flow – through mesocosms can be replicable when located near to the source system and allowed to establish naturally.     

Identifying Sites for Elk Restoration in Arkansas

Abstract: We used spatial data to identify potential areas for elk (Cervus elaphus) restoration in Arkansas. To assess habitat, we used locations of 239 elk groups collected from helicopter surveys in the Buffalo National River area of northwestern Arkansas, USA, from 1992 to 2002. We calculated the Mahalanobis distance (D²) statistic based on the relationship between those elk-group locations and a suite of 9 landscape variables to evaluate winter habitat in Arkansas. We tested model performance in the Buffalo National River area by comparing the D² values of pixels representing areas with and without elk pellets along 19 fixed-width transects surveyed in March 2002. Pixels with elk scat had lower D² values than pixels in which we found no pellets (logistic regression: Wald χ² = 24.37, P < 0.001), indicating that habitat characteristics were similar to those selected by the aerially surveyed elk. Our D² model indicated that the best elk habitat primarily occurred in northern and western Arkansas and was associated with areas of high landscape heterogeneity, heavy forest cover, gently sloping ridge tops and valleys, low human population density, and low road densities. To assess the potential for elk-human conflicts in Arkansas, we used the analytical hierarchy process to rank the importance of 8 criteria based on expert opinion from biologists involved in elk management. The biologists ranked availability of forage on public lands as having the strongest influence on the potential for elk-human conflict (33%), followed by human population growth rate (22%) and the amount of private land in row crops (18%). We then applied those rankings in a weighted linear summation to map the relative potential for elk-human conflict. Finally, we used white-tailed deer (Odocoileus virginianus) densities to identify areas where success of elk restoration may be hampered due to meningeal worm (Parelaphostrongylus tenuis) transmission. By combining results of the 3 spatial data layers (i.e., habitat model, elk-human conflict model, deer density), our model indicated that restoration sites located in west-central and north-central Arkansas were most favorable for reintroduction.     

Factors driving extreme sexual size dimorphism of a sit-and-wait predator under low density

Sexual size dimorphism is often a likely outcome of the interplay between natural selection and sexual selection, with female size dictated primarily by natural selection that maximizes fecundity and male size by sexual selection that maximizes reproductive opportunities. Attention to male fitness has focused heavily on direct male-male conflict selecting for superior male size and/or fighting ability, although male reproductive traits vary immensely among animals. An alternative, advanced by Michael Ghiselin, posits highly mobile dwarf males as a strategy for finding relatively immobile females in low-density populations. Adult male crab spiders Misumena vatia , sit-and-wait predators, are strikingly smaller, much more active, and relatively longer-legged than their females. This size difference results largely from males having two fewer instars than females, which simultaneously results in marked protandry. Populations of M. vatia often were small and of low density, with a female-biased sex ratio and an operational sex ratio that changed strikingly over the season. Sexual selection through scramble competition (locating the female first) should favour this suite of characters in males of low-density populations. Although direct male-male contests favoured large males, the low densities of adult males and the dispersed, relatively immobile females led to low levels of direct intrasexual contest. Females exaggerated the problem of males in finding them by providing few cues to their presence, a pattern consistent with indirect mate choice. In addition to favouring high mobility, scramble competition favoured males that selected flowers attracting many prey, the sites most often occupied by females.     

A quantitative analysis of the abundance and demography of European hares Lepus europaeus in relation to habitat type, intensity of agriculture and climate

1. European hares Lepus europaeus have declined throughout Europe since the 1960s. Possible reasons for this include agricultural intensification and changes in climate and predator numbers, but no clear consensus has been reached as to the relative importance of each of these. We aimed to identify factors associated with high and low hare numbers throughout Europe, to determine which could have caused population declines. 2. Results of 77 research papers from 12 European countries were summarized. Relationships between hare density and demographics and habitat, climate, hunting and predator variables were examined and quantified where possible. Temporal changes in factors identified as being associated with high or low numbers of hares were then examined to see if they could explain population declines. 3. Data from pastural habitats were limited, but densities of hares were low. Arable habitats had higher densities than mixed areas in spring, unless farming was intensive in which case densities were similar. In autumn the two habitats had similar densities. Field size, temperature, precipitation and hunting had no effect on density throughout Europe. Fecundity was affected by climate. 4. Arable land, various crops, fallow habitat and temperature were positively associated, and monoculture, precipitation and predators negatively associated with hare abundance. The relationship of field size, pasture and woodland with abundance depended on spatial scale. 5. Habitat changes caused by agricultural intensification are the ultimate cause of hare population declines. Effects of changes in climate or predator numbers are magnified by the loss of high-quality year-round forage and cover. Further research is required on how habitat changes affect fecundity and survival, and to identify which parameters have the greatest impact on population numbers. Farmland management policies that target the re-establishment of some of the habitat diversity lost within fields, farms and landscapes will help to reverse the decline of the European hare.     

Tracking palustrine water seasonal and annual variability in agricultural wetland landscapes using Landsat from 1997 to 2005

Wetlands densely populate the ecoregion transecting the center of the Prairie Pothole Region (PPR) known as the Missouri Coteau and epicenter to the most productive waterfowl‐breeding habitat in North America. These palustrine, depressional basin waters vacillate with regional drought and deluge, so surface water fluctuations over time modulate wetland productivity, habitat, and water quality functions. Models predict formidable effects of climate change on glacial basin surface waters, yet large‐scale, long‐term observation data are lacking to compare against predicted changes. Current, optical‐based water detection models do not delineate marsh vegetation from shallow, turbid, high‐chlorophyll waters common to the region. We developed a palustrine wetland spectral model for tracking open surface waters using Landsat imagery, which we evaluated for a 2500 km² landscape that estimates seasonal and annual open water variability for thousands of individual wetlands in the Missouri Coteau ecoregion. Detection accuracy of 96% was achieved for water bodies greater than a half‐pixel in size. We identified shifts in the distribution of water permanence classes within and between years for waters emerging in spring, mid‐summer, and late summer from 1997 to 2005 and identified a maximum of 19 047 basins with open water (12% of the landscape) populating 2500 km². For the 2005 growing season, we observed only 8757 basins with open water (6% of the landscape) for the same area. Declines were greatest for water bodies detected only in spring, suggesting a loss of those wetlands functioning to recharge groundwater stores early in the season and a high sensitivity to observed reductions in snowfall. If landscape factors driving open water coverage and wetland density are similar for the entire Missouri Coteau, we estimate the number of basins containing at least a pixel of water for this region declined from 577 600 to 266 000 between 1997 and 2005.     

Isolation and characterization of di‐ and tetranucleotide microsatellite loci in the yellow‐spotted night lizard Lepidophyma flavimaculatum (Squamata: Xantusiidae)

We report the development of 17 di‐ and tetranucleotide microsatellite markers in the Yellow‐Spotted Night Lizard Lepidophyma flavimaculatum. Levels of heterozygosity ranged from 0 to 100%. Several loci also amplify in other Lepidophyma species and several species of the sister genus Xantusia. High levels of variation at some loci indicate that they will be useful for parentage assessment and population genetic studies, whereas the 15 loci that amplify across multiple Lepidophyma species suggest these will be useful in determining the origin of parthenogenetic populations.