Habitat associations of pool-breeding amphibians in eastern Massachusetts,USA

There is a pressing need to develop a sound conservation strategy for pool-breeding amphibians, which includes gaining a better understanding of the habitat and landscape-scale characteristics associated with populations. To investigate relationships between amphibian species richness and characteristics of breeding pools and surrounding landscapes, we surveyed 85 pools in eastern Massachusetts (USA) in 1996 and 1997. A total of 11 species was detected, with most pools having 2–5 species. Pools were typically small, 77.6% were <0.2 ha, but most pools (72%) had hydroperiods that persisted at least into August in most years. Based on linear regression analyses, species richness was positively associated with three within-pool variables (pool surface area, hydroperiod, and the amount of emergent vegetation), and a landscape-level variable (presence of another breeding pool within 1 km), while one within-pool variable (tree canopy cover) exhibited a significant negative association with species richness. These within-pool habitat variables and connectivity to other breeding pools are important characteristics to consider when attempting to identify breeding sites that could provide core habitat in conservation reserves designed for the conservation of pool-breeding amphibian species richness. Conservation reserves for pool-breeding amphibian populations should include pool complexes functioning as habitat for metapopulations. Core pool habitats within such reserves should be large (0.5–1.0 ha), with seasonal hydroperiods that persist into August or that dry in some years, and with sufficient emergent vegetation to provide diverse microhabitats and refugia.     

Taxonomic distinctness and aquatic Coleoptera: comparing a perennial and intermittent stream with differing geomorphologies in Hidalgo, Mexico

Taxonomic distinctness combines species richness and phylogenetic diversity to detect changes in taxonomic structure. Most studies have reported on changes due to marine impacts, with little emphasis on habitat influences or freshwater systems. The composition and organizational structure of aquatic Coleoptera assemblages are susceptible to local influence, yet their colonization capacities suggest greater assemblage similarity over larger spatial scales. Surveys were conducted in two contrasting local streams (approximately 20 km apart), one intermittent with multiple stair-step cascades and intervening pools during the rainy season (and only pools during the dry season), and the other perennial with low gradient, in Hidalgo, Mexico. Published information from these initial surveys and their associated collections of adults were examined and the data converted to monthly presence/absence data for analysis using taxonomic distinctness. Despite reported physicochemical differences between the streams, only the average monthly proportion of swimmer species was significantly higher in the intermittent stream where elmids and psephenids were largely missing due to the general absence of protective substrate and the presence of pools; higher taxonomic structure was not affected. Well-developed colonization capabilities and a widely distributed species pool likely reduced detectable differences between the stream assemblages. Although the average monthly value of Sorenson’s Similarity Index for aquatic Coleoptera between both streams was low, differentiation was not achieved using taxonomic distinctness and presence/absence data.     

California vernal pool endemic responses to hydroperiod,plant thatch,and nutrients

Many endemic large branchiopods inhabit ephemeral freshwater ecosystems, including California vernal pools. Hydroperiod, inundation length, has been well studied in these systems that cycle between aquatic and terrestrial phases, but species’ responses to other ecological processes are still poorly known. For example, temporal (plant thatch from the previous terrestrial phase) and spatial (nutrient runoff) factors may have strong effects on emergence and population densities during the aquatic phase. We examined the effects of hydroperiod stability, thatch, and nutrients on the emergence and density of 4 vernal pool endemic species: Branchinecta lynchi (Anostraca), Linderiella occidentalis (Anostraca), Lepidurus packardi (Notostraca), and Cyzicus californicus (Spinicaudata). A full factorial mesocosm experiment was conducted which measured species densities, along with water quality variables. Hydroperiod and thatch differentially affected 3 of the 4 species based on emergence timing and life cycle. Treatments had effects on many water quality variables, and these variables were correlated with densities. These results highlight how hydroperiod stability along with other processes can affect large branchiopod species in temporary freshwater ecosystems. California vernal pools are a greatly reduced habitat rich in endemic and endangered species (including Branchinecta lynchi and Lepidurus packardi), and therefore, these results have implications for conservation and management.     

Biomass, species composition and diversity of epipelic algae in mire pools

The biomass, species composition and diversity of epipelic algae in two small pools of contrasting physicochemical characteristics in Miyatoko Mire were studied in 1992 (pool 3 =site B4 and pool 50 =site D2). A total of 93 species and 67 species of epipelic algae occurred at sites B4 and D2, respectively. Considerable differences were observed between the two sites in the seasonal fluctuations of species number, biomass and dominant species. At site B4, little changed with species number during April–August and markedly increased in October, while biomass was largest in April and gradually decreased during June–October. Diatoms and desmids occupied 33–82% and 15–63% of total algal biomass, respectively. At site D2, species number and biomass were small in April just after the snow-thaw, and increased in June and decreased in August and October. Diatoms occupied 90–98% of total algal biomass. The species diversity was always higher at site D2 than B4. As a result of analyses of water chemistry in the two pools, pool B4 can be recognized as a habitat experiencing high disturbance frequency. It is predicted that pools experiencing frequent disturbance will have less epipelic algal biomass and diversity.     

Distribution of aquatic macroinvertebrates within peatland pool complexes in the Flow Country, Scotland

Stationary water traps were used to sample the aquatic invertebrates from both shallow, drought-sensitive pools and deeper, more permanent pools on blanket bog in the Flow Country, northern Scotland during 1994–1995, an area important for nature conservation. The differences in numbers of invertebrates trapped, and the differences in species composition and abundance of adult aquatic Coleoptera and Hemiptera (the two most abundant groups caught) between these two pool types, and spatially within the deeper pools, were investigated. Using the same trapping effort, seven times more invertebrates and five times more adult Coleoptera were taken in the deep (A4) pools compared to the shallow (A3) pools, and Hemiptera were almost exclusively trapped in the A4 pools (only 2% of the catch was from A3 pools). DECORANA showed that the Coleoptera species composition of the two pool types was different, although a small overlap existed, presumably because of the proximity of the pool types and of the continuous nature of the variation between them. There was little difference in the numbers taken or species composition of Coleoptera or Hemiptera from the edges or centre of the A4 pools. Smaller Coleoptera species were found in both pool types, although one species was more common in the centre of the larger pools. Larger Coleoptera with a body length of more than 11.6 mm were not found in the A3 pools, only in the deeper A4 type. The A4 pools were found to be more stable seasonally than the shallow pools with respect to invertebrate numbers trapped, and this may be linked to the chance of drying out of the latter in dry periods. The influence of pool stability (through water level) on invertebrate abundance, development and individual species size is discussed, as is the sampling method used, the significance of the peatland fauna and its importance to breeding bird life associated with peatland pool complexes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Emergence phenology and ecology of aquatic and semi-terrestrial insects on a boreal raised bog in Central Finland

Emergence of peatland insects was studied in Central Finland by sampling insects on a raised bog with tent traps from five different surfaces: muddy hollow without vegetation; hollow covered with Sphagnum ; deep (0.7–0.9 m) open-water pool; shallow (about 0.3 m) pool with bottom covered by Carex vegetation; shallow (about 0.3 m) pool with bare muddy bottom. The material was collected at two-days intervals from 13 May until 31 August in 1981.
Biomass emerging from the sites varied considerably. In general, aquatic sites were clearly more productive than semi-terrestrial sites. Corrected total biomass values for deep pools, shallow Carex pools, and shallow mud pools were 2.471, 1.066, and 0 514 g m⁻², respectively. The corresponding values for muddy and Sphagnum hollows were 0.208 and 0.236 g m⁻², respectively.
All chironomids, chaoborids and trichopterans from the aquatic sites were identified to species, and their emergence phenology and habitat preferences are discussed. 14 species were considered as eurytopic littoral species, 9 species showed strong preference for the bog pools or polyhumic lakes, and 8 species were of diverse origin. Differences in emergence patterns and habitat preferences are probably connected with species-specific resistances to freezing and oxygen and nutrient requirements. The role of emerging insects in the peatland food webs, especially as food for breeding birds, is briefly discussed.     

Hydrothermally generated aromatic compounds are consumed by bacteria colonizing in Atlantis II Deep of the Red Sea

Hydrothermal ecosystems have a wide distribution on Earth and many can be found in the basin of the Red Sea. Production of aromatic compounds occurs in a temperature window of ∼60–150 °C by utilizing organic debris. In the past 50 years, the temperature of the Atlantis II Deep brine pool in the Red Sea has increased from 56 to 68 °C, whereas the temperature at the nearby Discovery Deep brine pool has remained relatively stable at about 44 °C. In this report, we confirmed the presence of aromatic compounds in the Atlantis II brine pool as expected. The presence of the aromatic compounds might have disturbed the microbes in the Atlantis II. To show shifted microbial communities and their metabolisms, we sequenced the metagenomes of the microbes from both brine pools. Classification based on metareads and the 16S rRNA gene sequences from clones showed a strong divergence of dominant bacterial species between the pools. Bacteria capable of aromatic degradation were present in the Atlantis II brine pool. A comparison of the metabolic pathways showed that several aromatic degradation pathways were significantly enriched in the Atlantis II brine pool, suggesting the presence of aromatic compounds. Pathways utilizing metabolites derived from aromatic degradation were also significantly affected. In the Discovery brine pool, the most abundant genes from the microbes were related to sugar metabolism pathways and DNA synthesis and repair, suggesting a different strategy for the utilization of carbon and energy sources between the Discovery brine pool and the Atlantis II brine pool.     

The macro-invertebrate communities of temporary pools in an intermittent stream in tropical Queensland

Nine pools were studied in an intermittent stream. They were close to each other but differed in size, substratum, amount of shade and duration of water presence. Initial conditions were set by wet season flooding, following which each pool developed its own character. Cluster analysis showed that communities changed substantially with time in both species composition and abundance, and that some initially similar communities diverged while some initially dissimilar ones converged.Principal Components Analysis showed that these community changes were due largely to the drying of the pools, and to seasonal effects. Specialised drying communities developed in the pools of longer duration (up to 8 months), but not in the short-lived pools (3–4 months). Apparently similar numerical responses in different pools were often caused by different suites of predominant species.The diversity of the fauna (total of 78 species) was high in comparison with similar habitats in non-tropical regions.The pattern of development of the pools' communities was much as expected from island biogeography theory, except that there was no relationship between species richness and duration and size of pools. The species complements were largely opportunistic, being governed by extreme environmental disturbance.     

No quarter: Lack of refuge during flow intermittency results in catastrophic mortality of an imperiled minnow

1. Many once-perennial rivers have become intermittent. Channel drying can result in fish mortality if refuges are not available. Understanding where refuges occur and if fishes use these refuges can provide insight for species persistence and help stakeholders manage limited resources. Streamflow diversions in the Rio Grande of New Mexico can result in >60 km losses of aquatic habitat, affecting up to 30% of the range of imperiled Rio Grande silvery minnow (Hybognathus amarus). Potential refuges include areas with perennial flow below diversion dams, isolated pools, and irrigation return flows.
2. We examined spatial and temporal patterns of both adult and young-of-year Rio Grande silvery minnow collected in isolated pools that formed during streamflow intermittency from 2009 to 2019. We hypothesised that: (1) Rio Grande silvery minnow would be more numerous in pools that persisted longer; (2) they would be more numerous in isolated pools located closer to upstream areas of perennial flow, due to upstream movement to escape drying; and (3) increased rate of aquatic habitat loss each day would result in more Rio Grande silvery minnow in isolated pools.
3. During the 12 years of the study, we counted Rio Grande silvery minnow in 3,985 isolated pools that formed during streamflow intermittency. We related counts of Rio Grande silvery minnow in each pool to the maximum pool depth, rate of loss of aquatic habitat that occurred that day, and distance each pool was to an upstream barrier. In 2016, we examined persistence of 290 isolated pools until complete desiccation or reconnection with continuous flows occurred, and the factors that influenced pool persistence.
4. Deeper pools persisted for longer, but depth had a small positive effect on counts of adult Rio Grande silvery minnow and no effect on counts of young-of-year in isolated pools. Adults were more numerous in upstream isolated pools, whereas young-of-year were more numerous in downstream isolated pools. Rate of channel drying had little effect on the numbers of adult Rio Grande silvery minnow in isolated pools, but more young-of-year were stranded when the rate of drying was faster. On average, pools persisted <4 days and 263 of 290 dried completely before continuous flows returned. Only 66 of 4,749 Rio Grande silvery minnow occurred in pools that did not dry completely.
5. Rio Grande silvery minnow did not appear to escape channel intermittency; instead, they became stranded in shrinking isolated pools that did not persist long enough to act as refuges for fishes. Lack of refuge during channel intermittency would result in catastrophic mortality of fishes through complete desiccation of pools if there were no management actions, such as translocating fish. To increase persistence through streamflow intermittency, conservation actions should match the species response to intermittency by ensuring the availability of perennial-water refuges at the appropriate spatial and temporal scale.

     

The large Branchiopoda (Crustacea) from temporary habitats of the Drakensberg region,South Africa

The Drakensberg forms part of the Escarpment which separates the coastal plain from the inland plateau in southern Africa. This mountain range runs for about 400 km along the KwaZulu-Natal/Lesotho border and into the Eastern Cape province of South Africa. Altitude ranges from 1500 to 3000 masl. Rock pools and tarns are the main type of temporary pool habitat in the Drakensberg. 90 different habitats were sampled over a four-year period and various physical and chemical characteristics of these pools are presented. Large branchiopods occurred in 26 of these habitats. Five Branchipodopsis and two Streptocephalus species composed the anostracan fauna, while Triops granarius was collected only from the summit of the Escarpment at one locality. Four genera of Spinicaudata are represented in the Drakensberg but the current state of the taxonomy of this group does not allow identification to species level. Absence of large branchiopods from a high percentage of temporary habitats could be attributed to predation or many pools may not be sufficiently ephemeral. Most pools were inhabited by a single species of large branchiopod. This could be a result of low levels of food resources in pools, as indicated by extremely low conductivities. Restricted food resources could also be the limiting factor in the distribution of Streptocephalus and Triops which are only found in pools with higher conductivities. Four of the five Branchipodopsis species are endemic to the Drakensberg pools. These habitats are also inhabited by a high diversity of ostracods and other micro-crustaceans. Most of the KwaZulu-Natal Drakensberg falls within conservation areas but the Lesotho and Free State localities could be threatened by future development.     

Predator–prey relationships within natural,restored, and created vernal pools

We performed a multiyear monitoring study to compare amphibian habitat quality among four natural, four restored, and six created pools. We used successful reproduction and metamorphosis of two vernal pool indicator species, the wood frog and spotted salamander, to represent desired outcomes. Ordination techniques were used to identify the aspects of habitat quality that were most correlated with desired outcomes. Previously published results indicated that pool depth, volume, and hydroperiod were among the best predictors of success, regardless of pool type. Observations in the first few years of monitoring also suggested that pools with longer hydroperiods had a greater abundance of aquatic predators of eggs and larvae of indicator species. This follow‐up study further explores and compares predator–prey relationships among pool types. We quantified within‐pool predator and prey abundance and diversity and collected another year of data on the reproductive success of indicator species. Our results confirmed that mean predator abundance was eight times higher in pools with longer hydroperiods. We documented a 96% decrease in wood frog survival rates in a semi‐permanent, natural pool following a 41% decrease in overhead canopy cover and an increase in green frog abundance. At the same time, wood frog reproductive success increased in nearby restored pools with lower predator abundance. Pools with the highest mean survival rates for the two indicator species combined were short‐ or long‐cycle pools (i.e. hydroperiod of 12–35 weeks) with low predator abundance (i.e. <1 organism L^?1) and greater proportions of arthropod prey relative to other food items.     

Short-term effects of a catastrophic beaver dam collapse on a stream fish community

Synopsis We examined the short-term effects of the natural catastrophic collapse of a beaver dam on downstream benthic insect density and fish community structure in a headwater tributary of the Mississippi River. The catastrophic collapse of the dam and ensuing flash flood resulted in a dramatic (< 90%) decrease in benthic insect density in riffle and pool habitats. Sixty days after collapse of the dam, insect densities in riffles were 62% of pre-collapse densities. Insect recolonization of pools was slower than for riffles; 60 days after collapse of the dam insect densities in pools were 8% of pre-collapse levels. Collapse of the beaver dam altered the structure of the downstream fish community by causing a short-term (2–4 days) influx of pond species, resulting in a brief increase in species richness and abundance. Fish species richness and abundance then decreased for 4–60 days to levels below those prior to the collapse.     

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.     

Fish species richness and incidence patterns in isolated and connected stream pools: effects of pool volume and spatial position

I tested the effects of pool size and spatial position (upstream or downstream) on fish assemblage attributes in isolated and connected pools in an upland Oklahoma stream, United States. I hypothesized that there would be fundamental differences between assemblages in these two pool types due to the presence or absence of colonization opportunities. Analyses were carried out at three ecological scales: (1) the species richness of pool assemblages, (2) the species composition of pool assemblages, and (3) the responses of individual species. There were significant species-volume relationships for isolated and connected pools. However, the relationship was weaker and there were fewer species, on average, in isolated pools. For both pool types, species incidences were significantly nested such that species-poor pools tended to be subsets of species-rich pools, a common pattern that ultimately results from species-specific differences in colonization ability and/or extinction susceptibility. To examine the potential importance of these two processes in nestedness patterns in both pool types, I made the following two assumptions: (1) probability of extinction should decline with increasing pool size, and (2) probability of immigration should decline in an upstream direction (increasing isolation). When ordered by pool volume, only isolated pools were significantly nested suggesting that these assemblages were extinction-driven. When ordered by spatial position, only connected pools were significantly nested (more species downstream) suggesting that differences in species-specific dispersal abilities were important in structuring these assemblages. At the individual-species level, volume was a significant predictor of occurrence for three species in isolated pools. In connected pools, two species showed significant position effects, one species showed a pool volume effect, and one species showed pool volume and position effects. These results demonstrate that pool size and position within a watershed are important determinants of fish species assemblage structure, but their importance varies with the colonization potential of the pools. Isolated pool assemblages are similar to the presumed relaxed faunas of montane forest fragments and land bridge islands, but at much smaller space and time scales. Received: 6 December 1996 / Accepted: 10 December 1996     

Assemblages of dytiscid predators and culicid prey in relation to environmental factors in natural and clear-cut boreal swamp forest pools

Assemblages of diving beetles (Dytiscidae) and mosquito immatures (Culicidae) were studied during 1987–1988 in 40 small, more or less temporary, snowmelt pools in spruce swamp forest and clearings at the Arctic Circle in Sweden. Larger pools were warmer than smaller ones, and clearing pools were warmer than forest pools. Temperature differences between pools remained high until late July. Twenty-one dytiscid species, representing three guilds, occurred in the pools, and individual pools had 1–13 species. Ten species occurred in both habitats. A few stenotopic species of boreal swamp forests had in clearing pools apparently been replaced by some species with a preference for more productive, often man-made habitats. Six Aedes species were collected in the clearing pools. Five of these were found in the forest pools, of which three had no mosquito larvae. Dytiscid assemblages in both habitats and culicid assemblages in clearing pools showed strong nested patterns.Abundance and species richness of both culicids and dytiscids were higher in clearing than in forest pools with an area >2 m² after that the effects of pool area had been accounted for (MANCOVA). In both habitats, abundance and species richness of both culicids and dytiscids were strongly and positively correlated with a linear combination of pool area, depth and temperature (Canonical Correlation). Increasing drought frequency of pools had a negative, less significant effect on the biota. In the clearing, the abiotic correlations with abundance were somewhat weakened chiefly by the relatively low abundance values from the largest pool.Distribution and mean abundance of individual dytiscid species were positively related in the clearing pools. Flying dytiscids were trapped in the larger (1.6 m²), but not in the smaller (0.07 m²) artificial pools, and the immigration rate was markedly higher on clearings than in forest. Dug pools were colonized faster on clearings than in forest. Even the flightless Hydroporus melanarius colonized dug pools during the first year.     

Recovery of conservation values in Central African rain forest after logging and shifting cultivation

Secondary forests in Central Africa are increasing in importance for biodiversity conservation as old growth forests outside the few protected areas are disappearing rapidly. We examined vegetation recovery in a lowland rain forest area in Cameroon based on a detailed botanical survey of old growth forest and different-aged logging gaps (5–27 years) and shifting cultivation fields (10–60 years). Our analysis focuses on the long-term recovery of botanical conservation values by analysing trends in vegetation structure, species composition, species diversity and levels of endemism and rarity. In the total survey (4.25 ha), we recorded 834 species of which 23% were endemic to the Lower Guinea forest region. The proportion of endemic species was high in shrubs and low in herbs. Geographic range and (local) rarity were not significantly associated. The proportion of rare species (relative frequency <10%) was high in woody climbers and low in trees. In logging gaps, recovery of all vegetation characteristics was relatively quick (5–14 years). Recovery in shifting cultivation sites took longer (30–60 years). Endemic species were found to be highly sensitive to shifting cultivation practices and even after 50–60 years the level of endemism was still significantly lower compared to old growth forest. The proportion of rare species was not significantly different between disturbed sites and old growth forest. We conclude that secondary forests can contribute to biodiversity conservation, e.g. as buffer zones around protected areas. However, this contribution should be assessed differently between land use types and widespread versus endemic species.     

Nitrogen mineralization dynamics in grass monocultures

Although Wedin and Tilman (1990) observed large differences in in situ N mineralization among monocultures of five grass species, the mechanisms responsible were unclear. In this study, we found that the species did not change total soil C or N, and soil C: N ratio (range 12.9–14.1) was only slightly, but significantly, changed after four years. Nor did the species significantly affect the total amount of N mineralized (per g soil N) in year-long aerobic laboratory incubations. However, short-term N mineralization rates in the incubations (day 1–day 17) differed significantly among species and were significantly correlated with annual in situ mineralization. When pool sizes and turnover rates of potentially mineralizable N (N_o) were estimated, the best model treated N_o as two pools: a labile pool, which differed among species in size (N_l, range 2–3% of total N) and rate constant (h, range 0.04–0.26 wk^–1), and a larger recalcitrant pool with a constant mineralization rate across species. The rate constant of the labile pool (h) was highly correlated with annual in situ N mineralization (+0.96). Therefore, plant species need only change the dynamics of a small fraction of soil organic matter, in this case estimated to be less than 3%, to have large effects on overall system N dynamics.     

Breeding habitat selection and larval performance of two anurans in freshwater rock-pools

I studied breeding habitat choice of common toad Bufo bufo and common frog Rana temporaria in 221 freshwater rock-pools on 15 small islands in the southwestern coast of Finland. I monitored tadpole growth rate in a number of rock-pools differing in size, competitors and predator regime. Furthermore, I carried out a short-term field experiment to investigate the effects of different predators on larval survival. Rana bred in pools of virtually all sizes, although the very smallest ones were usually avoided. A logistic regression analysis showed that the amount of aquatic macrophyte vegetation and pool surface area were the most important pool characters for Rana. Bufo preferred the largest pools, and pool surface area was by far the most important habitat variable. Rana avoided pools with the lowest pH. but was more common than expected at pools with pH around 6. In Bufo such an effect was not found, but this may be due to relatively low number of pools occupied by Bufo. In Rana there was a positive correlation between pool area and tadpole body length in early June, but two weeks later this relationship was not significant. In Bufo tadpole body size was not significantly affected by pool area. Presence of predators or presence of the other tadpole species did not affect growth or tadpole body size in either Rana or Bufo. A short-term experiment in wading pools indicated that both species suffered heavy mortality in the presence of a diving beetle larva. In the presence of predatory fish, mortality of Bufo did not differ from controls, whereas mortality was high among Rana tadpoles. It appears that although predators prey heavily on Rana tadpoles, they do not exclude Rana from larger rock-pools. However, it is not evident from this study why Bufo avoids smaller pools.     

Livestock grazing affects vernal pool specialists more than habitat generalists in montane vernal pools

Questions

Do livestock grazing and seasonal precipitation structure species composition in montane vernal pools? Which grazing and precipitation variables best predict cover of vernal pool specialists and species with broader habitat requirements? Is vernal pool species diversity correlated with livestock exclosure, and at what spatial scales?

Location

Montane vernal pools, northeast California, USA.

Methods

Vegetation was sampled in 20 vernal pools, including pools where livestock had been excluded for up to 20 years We compared plant species composition, functional group composition and species diversity among sites that varied in grazing history and seasonal precipitation using CCA and LMM.

Results

Although vernal pool specialists were dominant in montane vernal pools, over a third of plant cover was comprised of species that occur over a broad range of wetland or upland environments. The species composition of vernal pool plant communities was influenced by both livestock grazing and precipitation patterns, however the relative effects of these environmental variables differed by functional group. Livestock exclosures favoured perennial vernal pool specialists over annual vernal pool specialists. In contrast, the cover of habitat generalists was more strongly influenced by seasonal precipitation than livestock grazing. At small spatial scales, species richness and diversity decreased as the number of years a pool had been fenced increased, but this relationship was not significant at a larger spatial scale.

Conclusions

Both livestock grazing and seasonal precipitation structure the montane vernal pool plant community. We found that livestock grazing promotes the cover of annual vernal pool specialists, but at the expense of perennial vernal pool specialists. Wetter vernal pools, however, support higher cover of wetland generalist species regardless of whether pools are grazed.