An Examination of Scale-Dependent Resource Use by Eastern Hognose Snakes in Southcentral New Hampshire

ABSTRACT The decline of many snake populations is attributable to habitat loss, and knowledge of habitat use is critical to their conservation. Resource characteristics (e.g., relative availability of different habitat types, soils, and slopes) within a landscape are scale-dependent and may not be equal across multiple spatial scales. Thus, it is important to identify the relevant spatial scales at which resource selection occurs. We conducted a radiotelemetry study of eastern hognose snake (Heterodon platirhinos) home range size and resource use at different hierarchical spatial scales. We present the results for 8 snakes radiotracked during a 2-year study at New Boston Air Force Station (NBAFS) in southern New Hampshire, USA, where the species is listed by the state as endangered. Mean home range size (minimum convex polygon) at NBAFS (51.7 ± 14.7 ha) was similar to that reported in other parts of the species’ range. Radiotracked snakes exhibited different patterns of resource use at different spatial scales. At the landscape scale (selection of locations within the landscape), snakes overutilized old-field and forest edge habitats and underutilized forested habitats and wetlands relative to availability. At this scale, snakes also overutilized areas containing sandy loam soils and areas with lower slope (mean slope = 5.2% at snake locations vs. 6.7% at random locations). We failed to detect some of these patterns of resource use at the home range scale (i.e., within the home range). Our ability to detect resource selection by the snakes only at the landscape scale is likely the result of greater heterogeneity in macrohabitat features at the broader landscape scale. From a management perspective, future studies of habitat selection for rare species should include measurement of available habitat at spatial scales larger than the home range. We suggest that the maintenance of open early successional habitats as a component of forested landscapes will be critical for the persistence of eastern hognose snake populations in the northeastern United States.     

Herbivory,current velocity and algal regrowth: how does periphyton grow when the grazers have gone?

1. An experiment conducted in streamside channels was used to document the regrowth of grazed periphyton. Our objective was to determine the relative importance of current velocity, grazing duration, and grazer type in shaping the trajectory of algal and periphytic regrowth. 2. The grazing mayflies Baetis bicaudatus and Epeorus longimanus were used alone and in combination to create three grazing treatments at slow, medium and fast current (2–5, 15–20 and 30–40 cm s^?1, respectively). Duration treatments consisted of 2, 4, 6, 8, 10 days of grazing. Chlorophyll a and ash‐free dry mass (AFDM) accumulation on grazed tiles was measured (as periphytic AFDM and chlorophyll a, respectively) at 2, 4, 6, 8 and 10 days following the removal of grazers. 3. Chlorophyll a and AFDM was best predicted by interactions between current velocity, grazing duration and regrowth time. 4. The two grazer species did not differ in their effect on Chlorophyll a and AFDM during the period of periphytic regrowth that followed grazing. 5. Longer grazing duration reduced periphytic biomass, but also accelerated algal regrowth, and this growth enhancement was more pronounced at slower current velocities. 6. Data from this study suggest that herbivory can have important historical effects on periphytic accrual.     

Evolution of the population structure of Venturia inaequalis,the apple scab fungus,associated with the domestication of its host

Evaluating the impact of plant domestication on the population structure of the associated pathogens provides an opportunity to increase our understanding of how and why diseases emerge. Here, we investigated the evolution of the population structure of the apple scab fungus Venturia inaequalis in response to the domestication of its host. Inferences were drawn from multilocus microsatellite data obtained from samples collected on (i) the Central Asian Malus sieversii, the main progenitor of apple, (ii) the European crabapple, Malus sylvestris, a secondary progenitor of apple, and (iii) the cultivated apple, Malus×domestica, in orchards from Europe and Central Asia. Using clustering methods, we identified three distinct populations: (i) a large European population on domesticated and wild apples, (ii) a large Central Asian population on domesticated and wild apples in urban and agricultural areas, and (iii) a more geographically restricted population in M. sieversii forests growing in the eastern mountains of Kazakhstan. Unique allele richness and divergence time estimates supported a host‐tracking co‐evolutionary scenario in which this latter population represents a relict of the ancestral populations from which current populations found in human‐managed habitats were derived. Our analyses indicated that the domestication of apple induced a significant change in the genetic differentiation of populations of V. inaequalis in its centre of origin, but had little impact on its population dynamics and mating system. We discuss how the structure of the apple‐based agrosystem may have restricted changes in the population structure of the fungus in response to the domestication of its host.     

FACTORS AFFECTING PUNGENCY OF MALT DISTILLATES AND ETHANOL-WATER MIXTURES

paungency is a physical sensation usually perceived as a component of flavor. Foods and beverages which are described as pungent often impart unpalatable sensations to those uninitiated in the experience. Variations in pungency were examined in whiskies, ethanol-water mixtures, and whisky model systems. Effects on sensory pungency of changes in composition showed that pungency in whisky is not only dependent on the concentration of ethanol in the headspace, but also on a complex of other effects.     

Litter quality, stream characteristics and litter diversity influence decomposition rates and macroinvertebrates

1. We examined the relative importance of litter quality and stream characteristics in determining decomposition rate and the macroinvertebrate assemblage living on autumn‐shed leaves. 2. We compared the decomposition rates of five native riparian tree species (Populus fremontii, Alnus oblongifolia, Platanus wrightii, Fraxinus velutina and Quercus gambelii) across three south‐western streams in the Verde River catchment (Arizona, U.S.A.). We also compared the decomposition of three‐ and five‐species mixtures to that of single species to test whether plant species diversity affects rate. 3. Decomposition rate was affected by both litter quality and stream. However, litter quality accounted for most of the variation in decomposition rates. The relative importance of litter quality decreased through time, explaining 97% of the variation in the first week but only 45% by week 8. We also found that leaf mixtures decomposed more quickly than expected, when all the species included were highly labile or when the stream environment led to relatively fast decomposition. 4. In contrast to decomposition rate, differences in the invertebrate assemblage were more pronounced across streams than across leaf litter species within a stream. We also found significant differences between the invertebrate assemblage colonising leaf mixtures compared with that colonising pure species litter, indicating non‐additive properties of litter diversity on stream invertebrates. 5. This study shows that leaf litter diversity has the capacity to affect in‐stream decomposition rates and stream invertebrates, but that these effects depend on both litter quality and stream characteristics.     

Interference with Deposition of Minerals in a Coccolithophorid Protozoon

Laboratory studies with axenic culture of the coccolithophorid,Hymenomonas MP 156, in chemically defined media have establishedthat this primitive protist deposits its minerals in essentiallythe same manner as multicellular organisms. An appreciable numberof inhibitors and natural compounds prevent deposition of mineralsin laboratory experiments. Among these cations other than Ca⁺²,certain amino acids, select intermediates of carbohydrate metabolism,and inhibitors of enzymes occupy a prominent place. Interferencewith deposition of minerals does not necessarily abolish proliferationof the coccolithophorid. However, electron-microscopic, autoradiographic,histological, and analytical studies of the various modes ofinterference reveal a profound alteration of organelles andphysiological activities. The ability of the protist to useits own extracellular, mineralized, calcareous structures asa source of Ca⁺² for growth under conditions of reduced cationsin the environment suggests a possible role for these microorganismsin cation equilibria of natural waters.