Egg Mass Abundance Research Articles

Egg-Mass Abundance and Within-Pool Characteristics for Three Species of Vernal Pool-Dependent Amphibians in a Massachusetts State Forest

Egg-Mass Abundance and Within-Pool Characteristics for Three Species of Vernal Pool-Dependent Amphibians in a Massachusetts State Forest

Facilitating the recovery of insect communities in restored streams by increasing oviposition habitat.

Recruitment limitation is known to influence species abundances and distributions. Recognition of how and why it occurs both in natural and in designed environments could improve restoration. Aquatic insects, for instance, rarely reestablish in restored streams to levels comparable to reference streams even years after restoration. We experimentally increased oviposition habitat in five out of 10 restored streams in western North Carolina to test whether insect egg-laying habitat was limiting insect populations in restored streams. A main goal was to test whether adding oviposition habitat in the form of rocks that partially protrude above the water surface could be used to increase the abundance and richness of stream insect eggs and larval insects in restored streams. Adding egg-laying habitat enhanced several response variables (e.g., protruding rocks, number of eggs, egg masses, egg morphotype richness, and oviposition habitat stability) to levels similar to those found in reference streams. Following the addition of protruding rocks, egg mass abundance increased by 186% and richness by 77% in restored-treated streams. Densities of larval insects that attached their eggs to protruding rocks showed an overall pattern consistent with treatment effects due to the combination of nonsignificant and significant increases of several taxa and not just one taxon. Our results indicate that these stream insect populations are limited by oviposition habitat and that adding egg-laying habitat alleviated this component of recruitment limitation. However, the weaker larval response indicates that additional post-recruitment factors, such as egg or larval mortality, may still be limiting a full recovery of larval insect abundances in these restored streams. This study shows the importance of integrating information from animal life histories, ecology, and geomorphology into restoration practices to improve the recovery of aquatic insects, which are commonly used to assess water quality and the biological efficacy of stream restoration.

An effective trap for spotted lanternfly egg masses.

Spotted lanternfly (SLF) (Lycorma delicatula (White)), an invasive planthopper discovered in Pennsylvania, USA in 2014, continues to spread and is now present in 14 states with substantial infestations present in seven states. Population projections using adult SLF trapping or visual counts are not reliable due to the transient, migratory behavior of the adults which make population forecasts difficult. Another approach to population monitoring is utilization of the stationary egg mass stage, but counting small cryptic egg masses throughout the canopy of large trees in dense woodlots is arduous and prone to error. After several field seasons testing various trapping configurations and materials, we have identified an efficient, simple, low-cost trap termed a 'lamp shade trap' that is attached to the lower trunk area of an SLF host tree. SLF females readily enter the trap and lay eggs on the thin, flexible trap surface. A vertical trap orientation was superior, and the most productive woodlots yielded an average of 47 and 54 egg masses per trap, and several traps had over 100 egg masses. There were 1,943 egg masses tallied from 105 traps placed at six locations in two states. Egg mass counts in the area above and below the traps and on nearby control trees yielded very few egg masses in comparison. Selection of trees 15 to 20 cm in diameter for trap placement is most efficient, yielding good egg mass abundance while minimizing the amount of trap material used. The lamp shade trap has potential as an effective tool to identify SLF in new areas, gauge SLF population levels in woodlots and can also be used to collect and monitor egg masses for research purposes.

Evaluating Chemical Cues Associated with Halyomorpha halys Toward Enhanced Sensitivity of Surveillance for Trissolcus japonicus.

In Asia, Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae) is the predominant egg parasitoid of the brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae). Detections of adventive T. japonicus populations in North America since 2014, where invasive H. halys populations have impacted various specialty crops, spurred surveillance efforts to track T. japonicus, and yellow sticky cards (YSC) deployed in H. halys host trees have proven effective for this purpose. While T. japonicus exhibits positive behavioral responses to several olfactory stimuli associated with H. halys under laboratory conditions, these have not been evaluated for their potential utility to enhance surveillance of T. japonicus in the field. In northwestern Virginia, where both H. halys and T. japonicus are well-established, we examined the effect of baiting tree of heaven, Ailanthus altissima (Mill.) Swingle (Sapindales: Simaroubaceae), with lures containing the H. halys aggregation pheromone and pheromone synergist on the abundance of H. halys egg masses and captures of T. japonicus in YSC. We also assessed the effect of baiting YSC with newly-laid H. halys egg masses or n-tridecane, a component of H. halys tarsal prints, on T. japonicus captures. Destructive sampling of pheromone-baited and nonbaited trees revealed no significant differences in H. halys egg mass abundance on foliage. Similarly, YSC deployed in pheromone-baited and nonbaited trees showed no significant differences in T. japonicus captures. Moreover, YSC augmented with H. halys egg masses or n-tridecane showed no increase in T. japonicus captures compared with nonbaited controls. The implications for surveillance of adventive T. japonicus are discussed.

Augmentative biological control of Halyomorpha halys using the native European parasitoid Anastatus bifasciatus: Efficacy and ecological impact

We report the first large-scale augmentative biological control project carried out in Europe against Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) using the native egg parasitoid Anastatus bifasciatus (Geoffroy) (Hymenoptera: Eupelmidae). During summer 2020, a total of 325,000 adults of A. bifasciatus were released at a rate of 1000 individuals/ha of orchard in 11 sites in Trentino-Alto Adige (Northern Italy). Parasitism parameters were compared between release and control (no release) sites, in which at least three egg masses naturally laid by H. halys were collected (for a total of 262 egg masses). Anastatus bifasciatus and Trissolcus mitsukurii (Ashmead) (Hymenoptera: Scelionidae) were the dominant parasitoids, but parasitism by both species fluctuated widely among sites. At release sites, A. bifasciatus showed a significantly higher discovery efficiency (31.4%) and parasitism rate (16.7%) of H. halys egg masses than at control sites (1.7% and 1.2%, respectively). Parasitism by A. bifasciatus was not dependent on egg mass abundance at release sites, but at control sites a host density-dependent response was revealed by a positive relationship between parasitism and number of H. halys egg masses. On the other hand, parasitism by the adventive T. mitsukurii was not affected by either the releases of A. bifasciatus or by the abundance of H. halys egg masses per site. In conclusion, augmentative releases of A. bifasciatus contributed to increasing its parasitization of H. halys, without causing any negative effects on parasitization by naturally occurring species.

Regulation of open populations of a stream insect through larval density dependence.

In organisms with complex life cycles, the various stages occupy different habitats creating demographically open populations. The dynamics of these populations will depend on the occurrence and timing of stochastic influences relative to demographic density dependence, but understanding of these fundamentals, especially in the face of climate warming, has been hampered by the difficulty of empirical studies.Using a logically feasible organism, we conducted a replicated density‐perturbation experiment to manipulate late‐instar larvae of nine populations of a stream caddisfly, Zelandopsyche ingens, and measured the resulting abundance over 2 years covering the complete life cycle of one cohort to evaluate influences on dynamics.Negative density feedback occurred in the larval stage, and was sufficiently strong to counteract variation in abundance due to manipulation of larval density, adult caddis dispersal in the terrestrial environment as well as downstream drift of newly hatched and older larvae in the current. This supports theory indicating regulation of open populations must involve density dependence in local populations sufficient to offset variability associated with dispersal, especially during recruitment, and pinpoints the occurrence to late in the larval life cycle and driven by food resource abundance.There were large variations in adult, egg mass and early instar abundance that were not related to abundance in the previous stage, or the manipulation, pointing to large stochastic influences. Thus, the results also highlight the complementary nature of stochastic and deterministic influences on open populations. Such density dependence will enhance population persistence in situations where variable dispersal and transitioning between life stages frequently creates mismatches between abundance and the local availability of resources, such as might become more common with climate warming.

Hydrological controls on oviposition habitat are associated with egg‐laying phenology of some caddisflies

Abstract Seasonal variation in resource availability can have strong effects on life histories and population densities. Emergent rocks (ERs) are an essential oviposition resource for multiple species of stream insects. The availability of ERs depends upon water depth and clast size, which vary with discharge and river geomorphology, respectively. Recruitment success for populations may depend on whether peak egg‐laying periods occur at times when ERs are also abundant. For multiple species that oviposit on ERs, we tested whether seasonal fluctuations in ER abundance were concurrent with oviposition phenology. We also tested whether high discharge drowned ERs for sufficiently long periods to preclude egg laying, and whether this problem varied between rivers differing in channel morphology and particle size distribution. We obtained a continuous timeseries of water level (WL) measured every 30 min for 2 years at sites on three rivers in south‐eastern Australia with similar hydrology but different geomorphology. A relationship between WL and ER numbers was determined empirically at each site and these relationships were used to predict ER availability over the 2 years. Egg masses of 10 species of caddisflies were enumerated each month for a year in one river to establish oviposition phenology. Abundance of ERs was inversely related to discharge in all three rivers. ERs were most abundant during autumn and scarce during spring. Site‐specific geomorphology resulted in skewed or multimodal distributions of ER abundance each year. Between years, catchment‐scale hydrometeorology mediated patterns of ER availability, despite the close proximity of sites. Temporal variance in ER availability was not consistently correlated with mean WL or WL variance. ER variance increased with WL variance, when WL was below a threshold equivalent to mean annual WL. Above this threshold, most ERs were likely to be submerged. Oviposition phenology varied strongly among the 10 species of caddisflies, with egg‐laying ranging from 1–2 months to year‐round. Temporal variations in ER and egg mass abundance were not correlated for most species. Below a threshold minimum number of ERs, egg masses were highly crowded onto the few available ERs, which is evidence that ERs were in short supply. For five species, high egg mass abundance was positively associated with periods of the year when the time above the threshold number of ERs was high. Unusually, two species laid most egg masses during winter and when the time above this threshold was short. Three species showed no association between egg mass abundance and time above this threshold; two of these species laid eggs year‐round. Regional hydrometeorology controlled the availability of ERs, but between‐river differences were sufficient to deliver different outcomes in the availability of oviposition sites between years and seasons. Caddisflies were rarely prevented from laying eggs but periods when ERs were in short supply created crowding, which may be associated with negative fitness effects on hatching larvae. Geomorphological controls on availability of oviposition resources may have strong implications for the coexistence of species that overlap in egg‐laying phenology. ​

Oviposition Site Selection in Three Glass Frog Species

Oviposition site selection is critical for the reproductive success of oviparous organisms. We investigated oviposition site selection in three species of glass frogs—Espadarana prosoblepon, Hyalinobatrachium valerioi, and Teratohyla spinosa—in northeastern Costa Rica. We conducted nocturnal visual encounter surveys to estimate glass frog egg mass abundance and characterize oviposition site features in streams of three different habitats (pasture, secondary forest, and mature forest). Our results show differential oviposition site selection among all three species depending on vegetation and stream features. Hyalinobatrachium valerioi and T. spinosa, which oviposit almost exclusively on the underside of leaves, selected smooth leaves, while E. prosoblepon, which oviposits on the upper side of leaves or in moss, used moss eight times more than expected on the basis of availability. Hyalinobatrachium valerioi was found on larger leaves than T. spinosa and E. prosoblepon. Teratohyla spinosa and E. prosoblepon both oviposited most frequently above slow-moving water, while H. valerioi oviposited most frequently above fast-moving water. Espadarana prosoblepon was the only species affected by habitat type and had higher abundances of egg masses in mature forest than in secondary forest and pasture. Our results suggest that microhabitat plays a larger role in oviposition site selection than larger habitat classification. We propose that appropriate riparian microhabitat is a critical factor in sustaining glass frog populations in modified habitats and highlight the importance of preserving riparian corridors in altered landscapes.

Selection of macrophytes by a generalist invertebrate herbivore and potential impacts for stream rehabilitation

Macrophytes play an important role as resource for herbivores. When they are introduced into streams by, rehabilitation projects herbivores might be attracted to this new food source. Thus, it is important to know the palatability of macrophytes, especially when high densities of herbivores with a high relative consumption rate (RCR) are present. Plant traits influencing herbivory could be an indicator for macrophyte selection in rehabilitation projects. In the laboratory, we assessed the RCR and preference of Pomacea canaliculata for Ludwigia peploides, Gymnocoronis spilanthoides, and Egeria densa, and linked it to plant chemical and structural traits. We also analysed the use of these macrophytes by the snail in plants transplanted into a recently dredged stream. The macrophyte beds transplanted were the only plants present in the stream. Plants and snails were sampled and snail egg masses quantified. In the laboratory, the RCR of E. densa was significantly lower than that of the other species, and the snails did not show any preference among macrophytes. The only trait related to palatability was dry matter content. The abundance of snails in transplanted beds was higher in E. densa and G. spilanthoides, and lower on L. peploides despite its highest coverage. The abundance of egg masses was the highest on G. spilanthoides. This indicates that Pomacea canaliculata exhibited active selection and differential use of transplanted macrophytes. In conclusion, L. peploides would be less affected by a generalist invertebrate herbivore and a suitable option to transplant into stream channels for rehabilitation projects.

Early Spring and Early Vanishing Wetlands as Harbingers of the Future? The Climate Change Trap for Ephemeral Pond-Breeding Frogs

The decline of the northern red-legged frog, Rana aurora, in the Pacific Northwest has been attributed to invasive species, habitat loss, and climate change. Rana aurora lay eggs on emergent vegetation, and larval development occurs in shallow, often ephemeral wetlands. In 2015 and 2016 we investigated how habitat and water quality parameters influence breeding productivity and development of R. aurora. Early season temperatures in southwestern British Columbia during both years were warmer than in the previous two decades and egg-laying occurred much earlier than any previous records, allowing us to follow the development of R. aurora under unusual climatic conditions. We monitored 43 wetlands in the Little Campbell River Watershed and nearby areas in 2015 and selected six sites to monitor tadpole metamorphosis. Peak egg mass abundance was inversely proportional to concentrations of nitrates and orthophosphates, and colder water appeared to support greater egg mass abundance. Although warmer ambient temperatures facilitated earlier onset of R. aurora breeding, we observed some egg mortality due to subsequent frost. Sites with earlier peak egg mass abundance dates did not exhibit earlier peak metamorph dates, nor did warmer water appear to facilitate quicker larval development. In 2015, one wetland dried up before tadpoles completed metamorphosis. The frog's reproductive cycle may adapt to warmer temperatures to some degree, but erratic precipitation or frost events could reduce R. aurora survivorship beyond recovery. The disruption of larval development we observed under unusually warm spring conditions provides a useful vantage point for predicting future impacts of climate change.

Predicting Anuran Abundance Using an Automated Acoustics Approach

Abstract Estimating abundance is critical in many areas of ecology and conservation biology. Despite this, methodological limitations prevent population monitoring at large spatial scales. Automated acoustic methods, such as recording devices and sound recognition models, can determine occupancy and phenology but have not been utilized to estimate abundance in amphibians. Here we evaluate a method to estimate the number of breeding female Wood Frogs (Lithobates sylvaticus) on the basis of the relationship between egg mass abundance and the acoustic activity of males, using an automated recognizer to count and quantify their vocalizations. We collected egg mass abundance data and recorded acoustic activity at sites in New Brunswick, Canada and the northern United States in 2015 and 2016. Egg mass abundance at a site was best predicted by the maximum daily number of calls on the basis of a model selection approach and the predictive ability of models (root mean square error ± 16–19 egg masses or 59–70%). Th...

Buffer-Mediated Effects of Clearcutting on In-Pool Amphibian Productivity: Can Aquatic Processes Compensate for Terrestrial Habitat Disturbance?

Natural resource extraction and wildlife conservation are often perceived as incompatible. For wetland-dependent amphibians, forested buffers may mitigate timber-harvest impacts, but little empirical research has focused on buffers around lentic habitats. We conducted a landscape experiment to examine how spotted salamander and wood frog reproductive output (i.e., eggmass and metamorph production) respond to clearcutting mediated by buffers of different widths (i.e., uncut, 30 m buffer, 100 m buffer) at ephemeral pools in an industrial forest. We found complex interactions between buffer treatment and reproductive output, which were strongly mediated by hydroperiod. Overall, reproductive output was most sensitive at 30 m-buffer pools and for salamanders, but responses diverged across productivity metrics even within these categories. Notably, for both cut treatments over time, while salamander eggmass abundance decreased, metamorph productivity (i.e., snout-vent length [SVL] and abundance) tended to increase. For example, average metamorph SVLs were predicted to lengthen between 0.2 and 0.4 mm per year post-cut. Additionally, typical relationships between reproductive output and hydroperiod (as indicated by the reference treatment) were disrupted for both species in both cut treatments. For example, long-hydroperiod pools produced more salamander metamorphs than short-hydroperiod pools in both the reference and 30 m-buffer treatments, but the rate of increase was lower in the 30 m-buffer treatment such that a long-hydroperiod pool in the reference treatment was predicted to produce, on average, 24 more metamorphs than a similar pool in the 30 m-buffer treatment. From a conservation perspective, our results highlight the importance of evaluating both terrestrial and aquatic responses to terrestrial habitat disturbance, since responses may be reinforcing (i.e., exert similarly positive or negative effects, with the potential for amplification in the aquatic habitat) or decoupled (i.e., operate independently or be negatively correlated, with responses in the aquatic habitat potentially dampening or counteracting responses in the terrestrial habitat).

Eventos reproductivos del caracol Pomacea flagellata (Mollusca: Ampullaridae) en la laguna de Bacalar, Quintana Roo, México

The freshwater snail Pomacea flagellata is native from Southeastern Mexico. Studies about this species are scarce and none has treated their reproduction. This snail has been exploited at Bacalar lagoon for many years, leading to a significant decrease in their abundance and currently, a permanent ban was proposed by the government. This work aimed to assess the temporal variations of mating frequency and the abundance of egg clutches of P. flagellata at Bacalar lagoon, as well as their relation with snails density and environmental variables. Sampling was done during the three climatic seasons: Rainy (July, August and September/2012), North or Cold fronts (December/2012 and January and February/2013) and Dry (March, April and May/2013) in 12 sampling stations located along the Bacalar lagoon. On each station a transect of 100 m length was set parallel to the edge, and the number of fresh egg clutches (pink color) laid over vegetation, rocks or manmade structures, were counted. In the water, three 50 x 2 m transects were set and the number of snails were counted as well as the mating frequency. Density of snails varied significantly among seasons, decreasing from the rainy to the dry season. There were no significant differences of snail abundance among months, nested in climatic seasons (ANOVA, p>0.05). During the rainy season the mating frequency was significantly higher than in the Norths, meanwhile in the dry season no mating were registered (Kruskal-Wallis, p˂0.05). Eggs clutches appeared from July to March. Density of egg clutches presented no differences between the Rainy and the North seasons (2.72 and 2.93 clutches/m, respectively), nonetheless during the dry season abundance of egg masses was significantly lower (0.1 clutches/m) (H, p˂0.05). Mating frequency was related with snail abundance (rs= 0.26; p<0.05) and water temperature (rs= 0.34; p<0.05) and the abundance of egg masses is related with snail abundance (rs= 0.46; p<0.05). In general, we observed that reproductive activity of P. flagellata at Bacalar lagoon is related with the warmer months and with higher rainfall. This finding is relevant to support the management of this resource in the region, so that to implement any management arrangement they must be aware that a temporal ban is necessary during the reproductive season at least.

Host Plant Use by the Invasive Halyomorpha halys (Stål) on Woody Ornamental Trees and Shrubs.

The brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) is an invasive plant-feeding insect native to eastern Asia. This herbivore is highly polyphagous, feeding on and damaging diverse plants, including field crops, vegetables, tree fruits, and ornamentals. Woody ornamental plants provide early- and late-season resources for adults emerging from and returning to overwintering sites, as well as feeding and breeding sites for H. halys throughout the growing season. In this study, we quantify the use of diverse plants by H. halys in two commercial nurseries in Maryland, recording data on the abundance of egg masses, early and late instar nymphs, and adults over a three-year study period. Our specific goals were to provide a quantitative comparison of the use of diverse plant species and cultivated varieties, identify non-hosts that could be used to create landscapes refractory to H. halys, and determine whether the use of plants varied across life stages of H. halys or the taxonomic status of plants. We found broad use of diverse plants in this study, identifying 88 host plants used by all life stages of H. halys. We also highlight the 43 plant taxa that did not support any life stage of H. halys and are thus classified as non-hosts. Interestingly, some of these plants were congeners of highly-used plants, underscoring high intrageneric and intraspecific variation in the use of plants by this polyphagous herbivore. We discuss how the selective planting of non-hosts, especially gymnosperms, may aid in reducing the agricultural and nuisance pest status of this invasive insect.

Effect of Road Proximity on Reproductive Effort and Movement Patterns of the Wood Frog (Rana sylvatica)

ABSTRACT Nearly half of the amphibian species in northeastern North America rely on vernal pools as their primary breeding habitat. The problem is that, because vernal pools are small and isolated, they are often left unmonitored and unprotected. A primary threat to both amphibians and vernal pools is habitat destruction and fragmentation, but our knowledge of the species-specific impacts of habitat loss and fragmentation on all phases of the amphibian life cycle are still rudimentary. The wood frog (Lithobates sylvaticus) was the focus of this research because it is considered the most common vernal pool indicator in Pennsylvania. The objectives of this study were to investigate the effect of road proximity on vernal pool hydrology and water chemistry, reproductive effort of wood frogs (i.e., numbers of egg masses deposited), and upland movement patterns of wood frogs. These parameters were compared between three isolated pools (&amp;gt; 1000 m from the nearest road) and two pools in a fragmented habitat (&amp;lt; 100 m from two roads) within a Pennsylvania state park. This study indicates that, although road proximity did not have a significant effect on vernal pool water chemistry and egg mass abundance was greater in the fragmented location, habitat fragmentation by roads did have a significant effect on the movement patterns of wood frogs in surrounding terrestrial habitat. At the isolated site where there were no barriers to movement, wood frogs were distributed randomly around the pools. However, wood frogs in the fragmented location were trapped at a lower frequency near roads than expected by chance, indicating that the presence of roads may reduce the amount of upland habitat utilized by adult wood frogs. Although this was a small and localized study, the results indicate the challenging nature of conserving species with complex life cycles in human dominated landscapes and highlight the importance of considering life-cycle and species-specific habitat requirements when designing vernal pool conservation plans.

Comparative influence of isolation, landscape, and wetland characteristics on egg-mass abundance of two pool-breeding amphibian species

The distribution and abundance of species are shaped by local and landscape processes, but the dominant processes may differ with scale and increasing human disturbance. We investigated population responses of two pool-breeding amphibian species to differences in local and landscape characteristics in suburbanizing, southeastern New Hampshire, USA. In 2003 and 2004, we sampled 49 vernal pools for spotted salamander (Ambystoma maculatum) and wood frog (Lithobates sylvaticus) egg masses. Using egg masses as a proxy for breeding-female population size, we examined the relative influence of five land-use and three isolation variables at two scales (300 and 1000 m) and five wetland variables on egg-mass abundance. For both species, road density at the landscape scale (1000 m) and hydroperiod most strongly predicted egg-mass abundance, with abundance decreasing as roads became denser and hydroperiods shortened. Wetland isolation was also an important predictor, with abundance greatest at more isolated pools, suggesting that both species concentrate at isolated pools when alternative breeding sites are scarce. Surprisingly, no 300-m parameters were strongly associated with salamander egg-mass abundance, whereas several landscape parameters were. In suburbanizing areas, it is at least as important to consider landscape-scale road density as to consider hydroperiod when designing conservation plans for these species. Furthermore, both isolated and clustered pools provide these species important habitat and may require protection. Finally, the conceptual framework for spotted-salamander management must be expanded so that spatial configuration at the landscape scale becomes a regular, integrated component of conservation planning for this species.

Oviposition site selectivity of some stream-dwelling caddisflies

Population dynamics depends upon the spatial distribution of individuals in heterogeneous environments. The various processes surrounding insect oviposition are central to understanding their population dynamics because the choice of oviposition site ultimately influences the survivorship and spatial distribution of their progeny. Aquatic insects are often assumed to have non-selective oviposition habits, but empirical data are scarce and selective oviposition may be quite common. We quantitatively sampled egg masses of stream-dwelling caddisflies (Trichoptera) that specialise in egg-laying on hard substrata underwater, in order to characterise oviposition site selectivity and test for communal oviposition. In a field survey of two Scottish streams, we sampled egg masses of three species, Polycentropus flavomaculatus, Hydropsyche siltalai, Rhyacophila dorsalis, with the aim of testing whether egg mass abundance varied with current (riffles vs. pools), location within the channel (margins vs. centre) and rock exposure (emergent vs. fully submerged). In one stream, we captured adults landing on emergent rocks and assessed whether females were modified morphologically for swimming. The egg masses of two species (P. flavomaculatus, H. siltalai) occurred primarily on submerged rocks in pool margins, and adult females had legs modified for swimming. In contrast, egg masses of R. dorsalis were most abundant on the underside of emergent rocks in riffles, and females were not modified for swimming. Communal oviposition was evident for all three species, with most egg masses aggregated on the minority of potential rocks. How females locate oviposition sites and the consequences of these highly specialised oviposition behaviours to the survival and spatial distribution of larvae now require investigation. The effects of these behaviours on population dynamics are likely to differ from terrestrial herbivores because oviposition sites are not food resources for these aquatic species.

Spatial analysis of gypsy moth populations in Sardinia using geostatistical and climate models

Spatial fluctuations of the Sardinian population of the gypsy moth Lymantria dispar (L.) (Lepidoptera: Lymantriidae) were characterized using geostatistical and climate models. Data on gypsy moth egg mass abundance recorded at 282 permanent monitoring sites from 1980 to 2004 were incorporated in a geographic information system with the vegetational, geomorphological and pedological features of the sites. Statistical analyses revealed that the relative outbreak frequency was related to the predominant host tree, slope and elevation of the monitoring sites, whereas there was no correlation between outbreak frequency and exposure and soil type. By using bioclimatic modelling, probability maps of gypsy moth outbreaks were generated. The model identified a probability surface with climatic conditions favourable to gypsy moth outbreaks and thus potentially subject to defoliation. The maps included 92 sites where outbreaks never occurred, suggesting that the Sardinian climate may not be a determinant factor for gypsy moth outbreaks. The geostatistical method cokriging with outbreak frequency as a covariate was found to be the most suitable technique to estimate gypsy moth egg mass abundance. Semivariograms showed spatial correlation of egg mass abundance within the range 18.5–53 km. The results obtained were used to create regional gypsy moth distribution maps by cokriging, which demonstrated the outbreak foci and different infestation levels at each monitoring area. These results can help to delimit the treatment areas and develop rational gypsy moth management programmes.

Differential Responses of Postmetamorphic Amphibians to Cattle Grazing in Wetlands

ABSTRACT Global amphibian declines have been linked to various anthropogenic land uses. Recent studies have documented negative impacts of cropland agriculture and deforestation on amphibians; however, few have examined potential impacts of cattle grazing in wetlands on resident amphibians. Therefore, we measured differences in number of captures and body size of postmetamorphic amphibians, egg mass abundance, and shoreline vegetation structure and composition between 4 wetlands with direct cattle access and 4 wetlands from which cattle were excluded on the Cumberland Plateau in Tennessee, USA. We captured amphibians at wetlands from March to August 2005 and 2006 using pitfall traps. Number of green frog (Rana clamitans) metamorphs captured at nonaccess wetlands was 2.5 times and 9.8 times greater than at wetlands with cattle access in 2005 and 2006, respectively. However, number of American toads (Bufo americanus) captured was 68 times and 76 times greater at cattle‐access wetlands in 2005 and 2006, respectively. In general, metamorph body size was negatively correlated with species‐specific capture rate. We detected no differences in egg mass abundance between cattle land‐use types. Height, percent horizontal cover, and percent vertical cover of shoreline vegetation were 74%,25%, and 84% greater, respectively, in nonaccess wetlands in 2005; vegetation trends were similar in 2006. Our results suggest that cattle impact amphibian populations but effects vary by species. Differences in postmetamorphic capture rate may be related to less emergent vegetation at cattle‐access wetlands. Although body size differed between land uses for metamorphs, these trends probably were short‐lived, because we did not detect differences in juvenile and adult body size between land uses for most species. Based on our findings, we suggest that fencing cattle from wetlands may be a prudent conservation strategy for some amphibian species (e.g., ranids), whereas other species (e.g., bufonids) may benefit from controlled grazing.

Conserving pool-breeding amphibians in human-dominated landscapes through local implementation of Best Development Practices

Seasonal forest pools in the northeastern USA are unique ecosystems whose functions are intimately associated with adjacent upland habitats. This connection, coupled with their small size and ephemeral surface water, has made conservation of pool resources challenging. Seasonal pools provide optimal breeding habitat for animals adapted to temporary waters including ambystomatid salamanders (Ambystoma spp.), wood frogs (Rana sylvatica LeConte), and some invertebrates and plants. To date, wetland conservation efforts have been primarily limited to 2 pathways: land use regulation and preservation. Although both of these pathways have the potential to conserve some pool resources, they are often insufficient to maintain an array of pools in the landscape that support local population dynamics of amphibians. We propose a third pathway – local land-use planning – that can complement regulatory and preservation efforts. This suite of strategies, embodied in our Best Development Practices (BDPs), recognizes that not all pools will be conserved; local governances will need to develop priorities for conservation. The BDPs encourage local governances to (1) proactively identify their pool resources, (2) rank those pools according to their relative ecological value, and (3) establish management procedures and apply recommended guidelines in accordance with the relative rankings. We recommend that pools be ranked using biological criteria (e.g., presence of listed species, presence of breeding species, and egg mass abundance) and on the availability and quality of adjacent terrestrial habitat. We recommend 3 management zones: the pool depression, the pool envelope (i.e., land within 30 m of the pool), and the critical terrestrial habitat (i.e., 30–230 m from the pool). Residential, industrial, and commercial development, which may compromise pool habitat (e.g., through building and road construction, site clearing, stormwater management, and lighting), should follow the recommended guidelines presented in Appendix 1 of this paper. Planning at the watershed level, using such tools as overlay zones, wetland ordinances, and easements, should lead to more effective, long-term management of, at a minimum, the most ecologically important seasonal forest pool resources and will provide developers with clear development guidelines. This process is already being successfully implemented in a number of New England towns.