Landscape context influences the abundance of amphibians and the strength of their food web interactions in small ponds

Many species, including most amphibians, undergo an ontogenetic niche shift (ONS) from an aquatic larval stage to a terrestrial adult stage. We use the ratio of aquatic to terrestrial habitat in a landscape as a tool to understand the influence of landscape context on the population growth of ONS species. The aquatic to terrestrial ratio (ATR) of habitats can be viewed as an analog to the influence of resource ratios on the population growth of consumers and depends on the degree to which each habitat type limits the growth of a given population. Population growth rates of shorter‐lived species tend to be more limited by demographic rates in early (aquatic) life stages. As a result, increasing the ATR should lead to a higher total population size in the landscape (and higher densities in the terrestrial habitat), but have little influence on the density of individuals in any given aquatic habitat. Alternatively, population growth rates of longer‐lived species tend to be more limited by demographic rates in later (terrestrial) life stages and increasing the ATR should have little influence on the total population size in the landscape, but decrease the density of individuals in any given aquatic habitat. We show that among‐landscape variation in the breeding‐pond densities of three widespread amphibians with contrasting life histories is consistent with this framework. Within‐pond densities of Pseudacris crucifer, a species with short‐lived adults, were not influenced by ATR, whereas within‐pond densities of Hyla versicolor, a longer‐lived member of the same family (Hylidae), declined as ATR increased. Ambystoma maculatum, a long‐lived salamander, also had lower densities in ponds with higher ATR. Because A. maculatum larvae are important predators in ponds, we use structural equation modeling to show that landscape context (ATR) can moderate community structure via direct (amphibian abundances) and indirect (prey species richness) effects.     

Fish assemblages in temporary ponds adjacent to 'terra-firme' streams in Central Amazonia

1. The effect of habitat structural features and physicochemical characteristics of the water on the composition and richness of fish assemblages in temporary ponds near streams were examined at three spatial scales: among ponds, among streams and between drainage basins, in a ‘terra‐firme’ (not subject to long‐term flooding) forest reserve in Central Amazonia. 2. The fish assemblage in temporary ponds was composed of subsets of 18 small‐bodied species widely distributed in the reserve. The assemblages had a nested subset structure, where smaller ponds contained subgroups of the species found in larger ponds. 3. Species composition and richness in temporary ponds were similar between drainage basins, although the fish assemblages in streams differed between basins. 4. Fish assemblage structure was influenced by local factors related to habitat structure, such as pond area and depth, canopy cover and hydroperiod. Physicochemical characteristics of the water in the ponds were similar between drainage basins and had little detectable effect on the structure of pond fish assemblages. 5. No correspondence was found between the composition, richness or abundance of fishes in the ponds and in stretches of the streams adjacent to the ponds. Therefore, it is not possible to predict the composition of these temporary pond fish assemblages from the fish assemblages found in adjacent streams.     

Are cladoceran diversity and community structure linked to spatial heterogeneity in urban landscapes and pond environments?

Biodiversity patterns in cladoceran communities were investigated in urban waterbodies in relation with residential land use, pond management, and waterbody environments. We evaluated species richness in the pelagic and littoral zones of eighteen waterbodies of a large Canadian city. Gamma diversity (26 species) observed at a small scale in the urban survey was important comparatively to large-scale surveys of lakes. Beta diversity ranged from 1 to 8 species among waterbodies. We tested if littoral species greatly contributed to regional diversity in urban waterbodies. Littoral species (Chydoridae, Ilyocryptidae, Macrothricidae, Polyphemidae) accounted for 58% of the total species pool. We distinguished five cladoceran assemblages associated to different waterbodies (temporary ponds, permanent lakes, and wetlands). Cladoceran communities were more diverse and variable in permanent lakes than in temporary ponds. Changes in cladoceran species assemblages among waterbodies were driven by variations in waterbody size and phosphorus enrichment, macrophyte and algal biomass, urban density, pond management practices, and the presence of potential predators as fish and macroinvertebrates. Our study indicates that both artificial ponds and lakes and natural wetlands are valuable habitats for the conservation of cladoceran biodiversity and rare endemic species in urban regions. Further research on pond management strategies promoting urban aquatic biodiversity should be undertaken.     

Leaf litter input mediates tadpole performance across forest canopy treatments

Understanding the mechanisms limiting the distributions of organisms is necessary for predicting changes in community composition along habitat gradients. In many areas of the USA, land originally cleared for agriculture has been undergoing a process of reforestation, creating a gradient of canopy cover. For small temporary wetlands, this gradient can alter abiotic conditions and influence the resource base of wetland food webs by affecting litter inputs. As distributions of amphibians and many other temporary wetland taxa correlate with canopy cover, we experimentally manipulated shade levels and litter types in pond mesocosms to explore mechanisms limiting species performance in wetlands with canopy cover. Most differences between ponds were mediated by litter type rather than direct effects of shading. Although all three amphibian species tested are open-canopy specialists, spring peepers were the only species to show decreased survival in shaded ponds. Pond litter type generally had strong effects on growth and development rates, with tadpoles of two species in grass litter ponds growing to twice the size of, and metamorphosing 7 days earlier than, those in leaf litter ponds. Contrary to our initial hypothesis, shade level and litter type showed very few significant interactions. Our results indicate that the effects of shading cannot be considered in isolation of vegetation changes in pond basins when evaluating the effects of forest succession on temporary pond communities.     

Macroinvertebrate distributions and the conservation value of aquatic Coleoptera, Mollusca and Odonata in the ditches of traditionally managed and grazing fen at Wicken Fen, UK

1. Water-filled ditches are an important ecological feature of lowland Britain. Originally dug to facilitate wetland drainage, ditches often provide refuges for aquatic flora and fauna of high conservation value.
2. The ditches, ponds and major waterways of a traditionally managed undrained fen and the ditches of a previously drained cattle-grazed fen meadow were sampled at Wicken Fen National Nature Reserve for Coleoptera, Mollusca and Odonata, and for physical, chemical and biological variables.
3. Multivariate analysis showed a clear division between ditches on the two fens, and between larger and smaller waterbodies.
4. Individual ditches possessed distinctive faunas. Ditch age and bank profile were important factors influencing faunal species composition.
5. Invertebrate distributions were shown to be significantly correlated with macrophyte distribution.
6. Waterbodies were ranked in terms of their species quality, using a point-scoring system; there was no correlation between rankings for the three invertebrate groups; only ditch age and detritus levels were correlated with species quality score (for Coleoptera).
7. Ditch management recommendations are discussed in the light of these results.     

An expert-based landscape permeability model for assessing the impact of agricultural management on amphibian migration

The persistence of pond-breeding amphibian populations is influenced on different spatial scales ranging from the individual breeding pond to surrounding habitat patches to landscape clusters of breeding pond populations. The connectivity among breeding ponds as well as the availability of suitable terrestrial habitats surrounding the ponds plays a major role in long-term viability of amphibian species. Besides road traffic and urban structures agricultural land activity can disrupt landscape connectivity through the use of pesticides, fertilizers and physical activity such as tillage. We developed an expert-based model to assess the impact of agricultural management measures on the migration area and terrestrial habitat availability for seven amphibian species. The model is based on a Habitat Suitability Index to identify suitable terrestrial habitats and includes a landscape permeability approach. Size of migration areas, connectivity of breeding ponds and number of reachable terrestrial habitats were modeled considering species-specific migration ranges and habitat preferences. We consider how pesticides application might lead to fragmentation and isolation of amphibian breeding pond populations. Therefore the potential disrupting impact of pesticides was simulated by inflating landscape resistance to medium and high migration cost. One amphibian species showed a decrease of migration area by 48.3% and a decrease of reachable terrestrial habitats by 41.5% at high migration costs. Three additional species showed a decrease of their migration areas between 31.5 and 35.7%. At increased migration cost, some of the investigated populations were isolated at breeding pond level or restricted to pond clusters. Our model could be used to prioritize conservation efforts for pond-breeding amphibians with adequate consideration of agricultural land use and its impact on amphibian migration.     

The role of emergent vegetation in structuring aquatic insect communities in peatland drainage ditches

Availability of macrophyte habitat is recognized as an important driver of aquatic insect communities in peatland drainage ditches; however, eutrophication can lead to the decline of submerged vegetation. While emergent vegetation is able to persist in eutrophicated ditches, vegetation removal, carried out during ditch maintenance, can reduce the availability of this habitat. In this study, we applied the landscape filtering approach to determine whether the absence of emergent vegetation is a habitat filter which structures aquatic insect communities in peatland drainage ditches under different trophic conditions. To this end, a field study was carried out in one mesotrophic (Naardermeer) and one eutrophic (Wormer and Jisperveld) peatland in the province of North Holland, The Netherlands. We assigned life history strategies to insect species and applied linear mixed models and redundancy analyses to taxonomic and functional aquatic insect community data. Our results indicate that while differences between peatlands primarily determine the species pool within each wetland, emergent vegetation acted as a secondary filter by structuring functional community composition within ditches. The eutrophic peatland was dominated by insects adapted to abiotic extremes, while species with good dispersal abilities were strongly related to emergent vegetation cover. This study demonstrates the applicability of life history strategies to provide insight into the filtering of species due to availability of emergent macrophyte habitat. To ensure greater diversity of insect communities in ditch habitats, it is recommended that some vegetation be spared during maintenance to leave patches from which insect recolonization can occur.     

The response of amphibian communities to fish and habitat features in Mediterranean permanent ponds

Generalized linear models were used to test the effect of fish, using ponds with and without fish and habitat features as covariates, on richness and abundance of amphibian species. Five fish species and six amphibian species were recorded in 60 permanent ponds located in central Italy. The choice of covariates (macrophyte cover and pond surface area) was made after studying the correlations. The richness of amphibian species was not significantly affected by fish presence or macrophyte cover, in line with previous studies, since almost all the fish species were non-predatory. However, abundance of urodeles (newts) was negatively affected by fish and positively affected by macrophyte cover. Although fish may strongly influence the abundance and composition of amphibian communities, the results indicate that the cover of aquatic macrophytes may increase the available habitat for amphibians and therefore their abundance. Anuran species preferred ponds where fish were present, since both groups preferred larger ponds. Concordance between fish and amphibian species composition was not found by the Mantel and Partial Mantel tests. This indicates that the fish assemblages do not predict which amphibian species occur in the pond.     

Breeding phenology and larval distribution of amphibians in a Mediterranean pond network with unpredictable hydrology

Understanding spatial and temporal breeding patterns in Mediterranean amphibian communities is urgent considering the rate of habitat loss. Breeding phenology and breeding habitat selection by amphibians were analysed through the monthly occurrence of larvae in a mosaic of 198 Mediterranean temporary ponds during three years. A generalized linear model (GLM) coupled with principal component analysis showed that, for almost all species, occurrence was significantly positively correlated to pond depth. In addition, pond openness negatively affected the presence of some species. Temporal breeding patterns varied among species. Some species exhibited flexibility in their breeding date (Pelobates cultripes, Pelodytes punctatus, Hyla meridionalis, Rana perezi), while others did not (Triturus marmoratus, Triturus helveticus, Bufo calamita). When faced with inter-annual hydrological variability, the first group had a more constant breeding success than the second. Variable hydrological conditions caused differential larval occurrence of species between years. These fluctuations might favour long-term persistence of the whole amphibian community. We finally discuss the implications of our results for the management of amphibian habitats in the Mediterranean region.     

The effect of fish and aquatic habitat complexity on amphibians

Fish introductions are considered one of the most widespread anthropogenic threats to aquatic ecosystems. Their negative impact on native amphibian communities has received increasing attention in recent years. We investigated the relationship between the introduced fish, emergent vegetation cover and native amphibians in man-made ponds generated by regulation and dam building along the Tarnava Mare Valley (Romania) during the last 40 years. We inventoried amphibians and fish inhabiting 85 permanent ponds and estimated habitat complexity focusing on emergent vegetation cover. Four amphibian species were found to be negatively associated with the presence of predatory fish. Species richness of ponds without fish and ponds without predatory fish did not differ significantly, whereas ponds containing only predatory fish had significantly lower amphibian richness. A significant positive relationship was found between the emergent vegetation cover and pond occupancy of six amphibian species and amphibian species richness. As a management recommendation, we suggest the restriction of fish introductions to non predatory fish and the maintenance of high emergent vegetation cover in the ponds. Handling editor: S. Declerck     

Size-structured effects of common carp on reproduction of pond-breeding amphibians

The role of fish in driving amphibian communities has been widely recognized. However, little is known about size-structured interactions between amphibian and fish populations. This study compared the taxonomic occurrence and densities of larval amphibians between unstocked ponds and ponds stocked with different age cohorts of common carp Cyprinus carpio differing in average body size. The average total densities of early and late breeding anurans known to be vulnerable to fish were by 1–2 orders of magnitude greater in the presence of young-of-the-year carp than that of older cohorts. The probabilities of occurrence of the most common taxa did not differ between ponds stocked with young-of-the-year fish and ponds free of carp, but were significantly larger in those ponds than in ponds stocked with large-size cohorts. No significant differences between pond categories were found for densities of unpalatable Bufo bufo larvae. In aquatic systems harbouring size-structured fish populations, a fish age/size gradient may explain differential habitat suitability for breeding amphibians better than the fish presence/absence dichotomy. When dominated by young cohorts incapable of predation or of adverse habitat alteration, fish-abundant waters are suitable for amphibian reproduction. Conversely, even a ‘non-predatory’ fish, after attaining large body size, may exert a detrimental impact on amphibian breeding success. These findings may be particularly important for amphibian conservation at pond fisheries characterized by spatial separation of age/size distributed stocks.     

Niche position, but not niche breadth, differs in two coexisting amphibians having contrasting trends in Europe

Aim We explored general habitat‐related explanations (niche breadth and niche position) to the contrasting status of two amphibian species that have largely overlapping ranges and habitats – the rare and declining crested newt (Triturus cristatus), and the more common smooth newt (Triturus vulgaris). These closely related and ecologically similar species provide an excellent opportunity to study those methodologically challenging hypotheses, and this is the first such study on amphibians. Location Denmark. Methods We derived multivariate habitat models from 27 characteristics of 210 ponds and their surroundings, and their occupation by newts. In addition to the model performance, niche breadths were compared using the mean beta diversity of amphibian communities in the presence of each newt species. Results For each newt species, the habitat models comprised three variables and correctly classified 74% of observations. Diverse invertebrate fauna (prey base) and shorter distances to other ponds inhabited by conspecifics were positive for both species, while the surrounding habitat (notably dry grasslands with forests) was important for the crested newt and the sediment type of the pond for the smooth newt only. Beta diversity of the amphibian communities of occupied ponds did not differ between the two newt species. Hence, in an area of frequent coexistence, habitat requirements of the species differed in key variables, not in the extent of specialization. Main conclusions Our study supported the niche position rather than the niche‐breadth hypothesis of rarity. We suggest that the rarity and/or continuing decline of the crested newt is related to the degradation of (semi)natural terrestrial habitats around suitable water bodies in Europe. Consequently, special restoration of such habitats has a high potential for the recovery of this rare species, while general pond management appeared more beneficial for the common smooth newt.     

Restoration of lost aquatic plant communities: New habitats forChara

In the Netherlands peat was excavated for fuel until 1950. This gave rise to waterbodies (called turf ponds) which were then colonized by aquatic plants. Succession resulted in different aquatic plant communities and more terrestrialized stages such as floating fens. Nature conservation authorities started to excavate new turf ponds in 1990(ca. 2 ha y^–1) with the aim to restore calcareous, mesotraphent ecosystems by totally setting back succession. A sequence of new species was revealed by mapping the aquatic vegetation from 1990 onwards.Chara spp. proved early colonizers, which was not expected because they have not been present in ditches and ponds in the area for the last 20 years. The denseChara vegetation prevents the resuspension of organic soil and contributes to keep the water column nutrient-poor and clear. ability of species such asStratiotes aloides to colonise the ponds from adjacent waterbodies is not possible because no open contact exists between a turf pond and a ditch. Management measures, such as re-introduction, have to be considered if the full-range of aquatic plant communities remains the goal.     

Effects of terrestrial buffer zones on amphibians on golf courses

A major cause of amphibian declines worldwide is habitat destruction or alteration. Public green spaces, such as golf courses and parks, could serve as safe havens to curb the effects of habitat loss if managed in ways to bolster local amphibian communities. We reared larval Blanchard's cricket frogs (Acris blanchardi) and green frogs (Rana clamitans) in golf course ponds with and without 1 m terrestrial buffer zones, and released marked cricket frog metamorphs at the golf course ponds they were reared in. Larval survival of both species was affected by the presence of a buffer zone, with increased survival for cricket frogs and decreased survival for green frogs when reared in ponds with buffer zones. No marked cricket frog juveniles were recovered at any golf course pond in the following year, suggesting that most animals died or migrated. In a separate study, we released cricket frogs in a terrestrial pen and allowed them to choose between mown and unmown grass. Cricket frogs had a greater probability of using unmown versus mown grass. Our results suggest that incorporating buffer zones around ponds can offer suitable habitat for some amphibian species and can improve the quality of the aquatic environment for some sensitive local amphibians.     

Amphibian‐mediated nutrient fluxes across aquatic–terrestrial boundaries of temporary wetlands

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Pond-Breeding Amphibian Species Richness and Habitat Selection in a Beaver-Modified Landscape

ABSTRACT Beaver (Castor canadensis) activity creates wetland habitats with varying hydroperiods important in maintaining habitat diversity for pond-breeding amphibians with significantly different breeding habitat requirements. We documented pond-breeding amphibian assemblages in 71 freshwater wetlands in Acadia National Park, Maine, USA. Using 15 variables describing local pond conditions and wetland landscape characteristics, we developed a priori models to predict sites with high amphibian species richness and used model selection with Akaike's Information Criterion to judge the strength of evidence supporting each model. We developed single-species models to predict wood frog (Rana sylvatica), bullfrog (R. catesbeiana), and pickerel frog (R. palustris) breeding site selection. Sites with high species richness were best predicted by 1) connectivity of wetlands in the landscape through stream corridors and 2) wetland modification by beaver. Wood frog breeding habitat was best predicted by temporary hydroperiod, lack of fish, and absence of current beaver activity. Wood frog breeding was present in abandoned beaver wetlands nearly as often as in nonbeaver wetlands. Bullfrog breeding was limited to active beaver wetlands with fish and permanent water. Pickerel frog breeding sites were best predicted by connectivity through stream corridors within the landscape. As beavers have recolonized areas of their former range in North America, they have increased the number and diversity of available breeding sites in the landscape for pond-breeding amphibians. The resulting mosaic of active and abandoned beaver wetlands both supports rich amphibian assemblages and provides suitable breeding habitat for species with differing habitat requirements. Land managers should consider the potential benefits of minimal management of beavers in promoting and conserving amphibian and wetland diversity at a landscape scale.     

黄河下游平原农业景观异质性对两栖类生物栖息地可用性的影响

以黄河下游典型平原农业景观封丘县为研究区,基于图论的分析方法,采用概率连通性指数(PC)和斑块重要值(dPC_k)表征池塘栖息地可用性程度,在地理信息系统和R软件的支持下,分析了两栖类物种在250、500、1000和2000 m不同扩散能力下,反映池塘栖息地组成和构型的池塘平均面积(MS)以及池塘数量(NP)、至道路的最近距离(DR)组合作用对池塘栖息地可用性的影响.结果表明: 两栖类栖息地的可利用性与池塘数量、池塘平均面积和至道路的最近距离关系密切.在250 m扩散能力下,池塘平均面积和池塘数量是决定池塘可利用程度高低的重要影响因素;在500 m扩散能力下,池塘平均面积和至道路的最近距离对栖息地可用性的影响最为显著;在物种相对较高扩散能力下(1000和2000 m),池塘平均面积和池塘数量是最主要的影响因素.在平原农业景观中,两栖类生物及其栖息地的保护要充分考虑池塘斑块的数量、平均面积以及至道路的最近距离.     

The impact of roadside ditches on juvenile and sub-adult Bufo melanostictus migration

The amphibian species play an important role in much ecosystem functioning. However, it is severely impacted by civil engineering, which causes a high level of amphibian mortality. This is partly because roads isolate the amphibians’ habitats, causing the amphibians to cross them, during which time they can be killed by vehicles. However, secondly, roadside ditches can also have a fatal impact on the amphibians when they fall into them. This study focuses on this second issue and comprises two parts: field experiments and control experiments in the laboratory. In the field experiments, research into the roadside ditch impact on juvenile/sub-adult Bufo melanostictus migration was carried out by looking at different combinations of the ditch's angle, construction material and depth, and amount of plant growth. In the control experiments in the laboratory, the main focus of the study was the relationship between the body length of the juvenile/sub-adult Bufo melanostictus and its maximum jumping distance and jumping height, and the maximum gradient that Bufo melanostictus could climb.This research indicates that amphibian migration should be taken into account when roadside ditches are being planned. Civil engineering should consider the needs of the amphibians’ living space and thereby reduce its impact on the amphibians’ original habitat, so that human beings live in harmony with nature.     

The dispersal and deposition of hydrochorous plant seeds in drainage ditches

1. Surface water is an important dispersal vector for wetland plant species. However, most previous studies on hydrochory (i.e. water dispersal) have focused on ecosystems with relatively rapid water flow. Therefore, there is a need to study such dispersal in slow‐flowing or stagnant waterbodies, such as drainage ditches, which might act as dispersal corridors between habitat patches. 2. To gain insight into the mechanisms by which seeds are transported in drainage ditches, the effect of the velocity of wind and water on the rate of transport of floating seeds of three wetland species (Carex pseudocyperus L., Iris pseudacorus L. and Sparganium erectum L.) was investigated. Furthermore, in release and retrace experiments with painted C. pseudocyperus seeds, a number of factors potentially determining the probability of seed deposition were investigated. 3. Net wind speed was found to be the main factor determining the rate at which seeds are transported in drainage ditches. No relation between water flow at middepth in the ditches and seed transport was found. Wind speed and flow at the water surface were positively related. The effect of wind speed on the rate of transport of floating seeds was greater for S. erectum seeds, because a greater ratio of their volume protrudes from the water, than for C. pseudocyperus and I. pseudacorus seeds. 4. The principal factors that determine seed deposition were aquatic plant cover, ditch slope and indentations in the ditch bank. Seeds changed direction if the wind direction changed, or if there was a bend in the ditch. The final pattern of deposition was related to mean net wind speed. Mean transport distance after 2 days varied between 34 and 451 m. 5. Unlike in rivers, seed transport in ditches was determined by wind speed and direction, enabling multidirectional seed dispersal. We conclude that in slow‐flowing waters, wind is a more important driver for hydrochorous seed transport than the flow of water. This sheds a new light on hydrochory and has important consequences for the management of otherwise fragmented wetland remnants.     

Livestock disturbances in Mediterranean temporary ponds: A mesocosm experiment with sheep manure and simulated trampling

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