Hydroperiod Length Research Articles

Which variables influence the structure and abundance of aquatic herbivorous assemblages in small forested Patagonian wetlands?

ABSTRACT Herbivores in wetlands are key organisms that shape the structure and composition of wetland plant communities (algae and vascular plants). The detritus produced by herbivory contributes to nutrient cycling and provides important resources for other organisms in the ecosystem. Due to their importance, we decided to survey a set of 12 seasonal wetlands located in Andean Patagonian forests. We registered the biotic and abiotic variables of each wetland and the diversity and abundance of herbivores. We found two groups of wetlands: short hydroperiod and long hydroperiod. Despite this, the structure of the communities was not related to the hydroperiod length, abundance, or species composition. In particular, the abundance of herbivores was explained by chlorophyll, pH and dissolved oxygen, among others. Their diversity and abundance were (in decreasing order): rotifers, copepods, cladocerans, caddisflies, and amphibians. Probably, the species found in these wetlands are well adapted to different hydroperiod regimens and, even in short hydroperiods, can complete their life cycle. The results found here do not match with the model of hydroperiod gradient; however, other variables not measured here, such as diversity and abundance of aquatic plants or predation by invertebrates, could impact the composition and abundance of herbivores in these wetlands.

Pond basin colonization by terrestrial vegetation indicates wetland deterioration

Abstract Efforts to conserve the pond network in the Doñana National Park are being threatened by groundwater overexploitation. The dramatic expansion of farming and tourism in nearby areas has caused a severe lowering of the water table, reducing pond hydroperiod length or even instigating pond desiccation. It is important to document the link between groundwater abstraction and pond deterioration with a view to decreasing human pressures on the park and preserving the pond network's singular biodiversity. Here, the gradual deterioration of one of the network's main ponds is described in detail by characterizing vegetation patterns within the pond's basin using orthophotos taken between 1956 and 2019. In the earliest images, the pond contained a wide central area of bare soil during its dry phase. This area was surrounded by reeds and had a line of Tamarix canariensis trees along its southern edge. Starting in 2000, the orthophotos showed the pond's gradual colonization by terrestrial vegetation. In tandem, pond hydroperiod decreased, as did the length of time the pond retained certain depths of water. In recent years, Tamarix trees finally fully invaded the pond's central area, which is surrounded by reeds and has scattered terrestrial bushes and pines. This invasion resulted from the pond's sparse inundation over recent decades, being the cover of trees related to the depth of groundwater, and is a clear sign of pond deterioration. More broadly, colonization by terrestrial vegetation has been observed in approximately 60% of the network's ponds. Colonization of temporary pond basins by terrestrial vegetation can be used as an indicator of deterioration and highlights the need for active restoration and management.

Carryover effects of pesticide exposure and pond drying on performance, behavior, and sex ratios in a pool breeding amphibian

AbstractNeonicotinoid pesticides are widely used to combat agricultural and forest pests, yet the extent of their biological effects and synergies with other stressors is not well understood, particularly for species with complex life cycles such as amphibians. While there is extensive research on the impacts of agricultural chemicals on amphibians (particularly larval stage), research on the effects of the new class of widely used neonicotinoid pesticides across life stages is lacking. In this study, we used aquatic mesocosm manipulations and terrestrial locomotor and behavior trials to evaluate demographic, behavioral, and fitness carryover effects of sublethal neonicotinoid pesticide (imidacloprid) exposure and hydroperiod length on the wood frog (Rana sylvatica), a model organism. We found that the interaction of imidacloprid exposure and shorter hydroperiod led to decreased larval survival to metamorphosis (0.54 ± 0.14, compared to control 0.75 ± 0.04). When exposed to their thermal optimum (18°C), individuals exposed to imidacloprid as larvae had higher terrestrial locomotor performance (284.08 ± 28.62 body lengths traveled) but also experienced the largest decreases in performance (147.88 ± 19.27 fewer body lengths traveled) after terrestrial imidacloprid exposure. In a 48‐h substrate choice experiment, post‐metamorphic frogs did not show behavioral avoidance of imidacloprid‐treated substrates. Finally, we observed a skewed juvenile sex ratio from imidacloprid treatments (~10% fewer males compared to control), and we were not able to assign 15.7% of individuals from imidacloprid treatments to either sex due to ambiguous reproductive organ morphology. Our empirical assessment of carryover effects of chemical exposure and pond drying provides insights into the physiological capacity of taxa with complex lifecycles to respond to contaminants experienced at multiple life stages and informs best practices for neonicotinoid pesticide use in forest settings and conservation strategies for pond‐breeding amphibians.

Population structure and genetic diversity of the threatened pygmy newt Triturus pygmaeus in a network of natural and artificial ponds

Pond physical characteristics (connectivity, hydroperiod) have shown to be highly relevant in explaining species presence, reproductive success, and survival in breeding-pond amphibians. However, few studies have addressed the influence that these factors may have on the genetic variability of pond populations. We examined genetic variation at 11 microsatellite loci in Iberian endemic, the pygmy newt (Triturus pygmaeus), from 58 breeding ponds in the Doñana National Park (Andalusia), including both temporary ponds and artificially deepened ponds that remain wet during the whole year. Temporary ponds are located in the North part of the region where the surrounding habitat-wet meadows-facilitates the connectivity among populations, whereas the deepest ponds (‘zacallones’) are located in the southern edge embedded in a matrix of unsuitable habitat (thickets and dry underbrush). We investigated genetic diversity and structure within and among ponds. Our results show that both regions (Doñana-North and Doñana-South) are well-differentiated and form two main clusters. We found higher genetic diversity within ponds from the North region, which also exhibited a higher degree of genetic admixture in comparison with populations from the southern edge. Although we found an isolation-by-distance pattern within each cluster, it arose due to the effect of a few isolated ponds located on the edge of each zone, suggesting the existence of substantial gene flow between ponds in the core area. According to our findings, landscape’s permeability to movement (pond connectivity) may constitute a more important factor than hydroperiod length in determining the genetic diversity and viability of pygmy newt populations in this area. Although Doñana populations show a good state, more peripheral and isolated populations present a more worrisome condition as a result of fragmentation and thus, require conservation efforts. Our study provides key insights that could help guide management practices of this threatened and poorly-studied salamander.

Ecology of Aedes vittatus (Diptera: Culicidae) in rock pools across agroecosystem in Northern Savanna, Nigeria.

This study focuses on modulating dexterity of some ecological variables of Aedes vittatus classically breeding in rocky habitats. The study provides a useful insight into ecological variables that underpin or hinder profuse breeding of Ae. vittatus in rock pools and its probable role in disease transmission. HANNA HI98129 pH/EC/TDS/TEMP meter was used in situ while standard protocols were used to determine other hydro-chemical variables. Aedes vittatus larvae were obtained with soup ladle and modified ladle dippers. D-frame net was used to capture macroinvertebrates while plankton net was used to obtain samples of microalgae. Tadpoles and water turtles were collected with fine mesh invertebrate net. Macrophytes were uprooted and identified at the Herbarium Unit, Department of Botany, Ahmadu Bello University, Zaria. The influence of physicochemical variables was correlated with distribution of Ae. vittatus using Principal Component Analysis. Regression and ANOVA were used to test for association between predictor variables and mosquito abundance and for the difference amongst inselbergs. Linear larval density of Ae. vittatus in rock pools which tapered across Guinea savanna were obtained from twenty-one sites with average density of 139.6 in Sudan savanna. Guinea savanna had an average larval density of 75.5 with lower subsets of moving average densities compared to Sudan savanna. One hundred and sixty-one aquatic insects belonging to four insect orders cohabited rock pools with Ae. vittatus. Toads and frogs' tadpoles were of Bufonidae and Pyxicephalidae families while water turtles belong to Emydidae. pH, TDS (ppm), EC (μs/cm) and alkalinity (mg/l) differed significantly (p<0.05) with the abundance of Ae. vittatus in rock pools. Temperature, depth, water hardness and total suspended solid had direct influence on the distribution of Ae. vittatus in rock pools across sites. Significant positive correlation exists between aquatic insects and abundance of Ae. vittatus. Hydroperiod length, concentration of nitrate and pH were determinants that leverage profuse breeding of Ae. vittatus and survival of rock pool biota. Results revealed that the bearing influence of rock pool variables is inevitable for breeding of Ae. vittatus. A well defined measure of efficacy incorporating indigenous communities for sustained vector control on inselbergs will go a long way in decimating population of Ae. vittatus and limit the risk of spread of yellow fever hitherto areas not thriving.

Community structure, species–habitat relationships, and conservation of amphibians in forested vernal pools in the Georgian Bay region of Ontario

Forested vernal pools serve an integral role in the recruitment of amphibians in glaciated northeastern North America. In south-central Ontario, vernal pools exist in relatively unimpacted forest networks, but the amphibian communities face uncertain challenges from anthropogenic-induced climate change. We surveyed amphibian larvae and collected measurements of habitat characteristics from vernal pools to collect baseline information on amphibian community structure and species–habitat relationships. Amphibian communities were influenced by hydroperiod length and canopy openness, and the relative abundances of early breeding amphibians were affected by changes in the structure of vegetation communities within pools. Our study suggests that, even across moderate ranges of breeding habitat characteristics, the structure of amphibian communities is dynamic. With anthropogenic-induced climate change leading to more drought-prone summers, the conservation of intact forests that support diverse wetland assemblages will be a necessary component of future legislation.

Natural history traits of the terrestrial breeding frog Batrachyla taeniata (Anura: Batrachylidae) in wet meadows of Patagonia

ABSTRACT Anurans have diverse reproductive modes, and some species of the austral forests of Patagonia have become specialized in terrestrial reproduction. Batrachyla taeniata is one of these species: it inhabits wetlands, lays its eggs during late summer and fall in terrestrial conditions, and has overwintering tadpoles. We studied a population of B. taeniata that breeds in wet meadows surrounded by native Patagonian forest and described its life cycle parameters (breeding phenology, egg development, and coexistence with other anurans) over two different years with contrasting hydroperiods. We also analyzed the effect of predatory insects on tadpole survival. Embryo development occurred in wet soil, which may be exposed to the sun or not, and took from 48 to 63 days to hatch. Free-swimming larvae overwintered in the wetland and coexisted in spring with pond-breeding anurans that varied in composition and abundance according to the wetland hydroperiod. The survivorship of B. taeniata tadpoles was significantly greater than that of P. thaul tadpoles when both were exposed to a free belostomatid predator. We consider that the terrestrial reproductive mode and life cycle of B. taeniata enable this species to survive in the variable biotic conditions determined by hydroperiod length.

Long-Term Patterns of Amphibian Diversity, Abundance and Nutrient Export from Small, Isolated Wetlands

Seasonally inundated wetlands contribute to biodiversity support and ecosystem function at the landscape scale. These temporally dynamic ecosystems contain unique assemblages of animals adapted to cyclically wet–dry habitats. As a result of the high variation in environmental conditions, wetlands serve as hotspots for animal movement and potentially hotspots of biogeochemical activity and migratory transport of nutrient subsidies. Most amphibians are semi-aquatic and migrate between isolated wetlands and the surrounding terrestrial system to complete their life cycle, with rainfall and other environmental factors affecting the timing and magnitude of wetland export of juveniles. Here we used a long-term drift fence study coupled with system-specific nutrient content data of amphibians from two small wetlands in southeastern Georgia, USA. We couple environmental data with count data of juveniles exiting wetlands to explore the controls of amphibian diversity, production and export and the amphibian life-history traits associated with export over varying environmental conditions. Our results highlight the high degree of spatial and temporal variability in amphibian flux with hydroperiod length and temperature driving community composition and overall biomass and nutrient fluxes. Additionally, specific life-history traits, such as development time and body size, were associated with longer hydroperiods. Our findings underscore the key role of small, isolated wetlands and their hydroperiod characteristics in maintaining amphibian productivity and community dynamics.

Complex hydroperiod induced carryover responses for survival, growth, and endurance of a pond-breeding amphibian.

Assessing carryover effects from the aquatic to the terrestrial stage of pond-breeding amphibians is critical as temperature and hydrologic regimes of temporary ponds continue to be altered as a result of climate change and other stressors. We evaluated carryover effects of hydroperiod length (50-62days) on amphibian survival, developmental rates, and locomotor performance using a model organism, the wood frog (Rana sylvatica), through aquatic and terrestrial mesocosm experiments with individual tests of locomotor performance. We found that shorter hydroperiods (50 days) had low larval survival (0.44 ± 0.03) compared to the 62-day hydroperiod (0.91 ± 0.09) and increased developmental rates, resulting in smaller sizes at metamorphosis. We did not find evidence of carryover effects on terrestrial survival three months post-metamorphosis with all hydroperiod treatments showing high terrestrial survival (0.88 ± 0.07). However, post-metamorphic frogs from the longer hydroperiod treatments grew faster and larger compared to individuals from shortest hydroperiods and performed significantly better during endurance trials at 18°C. Disentangling complex carryover effects across multiple life stages in species with high phenotypic plasticity can shed light on the physiological capacity of species to respond to changing environments and inform mechanistic predictions of persistence in the face of anthropogenic stressors.

Effects of hydroperiod on morphology of tadpoles from highland ponds

Hydroperiod length has been identified as a major driver in community assembly in freshwater systems. Yet we generally lack an understanding of how morphological traits respond to water level decrease under natural conditions. Here, we studied variation in body size and shape in lateral view in tadpoles of Scinax squalirostris and Odontophrynus americanus inhabiting ponds in superhumid highland plateau in southern Brazil. Hydroperiod did not affect tadpole size in either species. In relation to body shape, S. squalirostris tadpoles from long hydroperiod ponds had shorter tails and deeper tail fins than tadpoles from other hydroperiods. Predator presence was positively associated with hydroperiod, restricting our ability to separate their effects on tadpoles morphology. For O. americanus, tadpole shape was not affected by pond hydroperiod. We demonstrated that, in natural environment, the influence of hydroperiod on tadpole morphology might depend on species-specific characteristics, such as behavior and life-history traits. Our results indicate that local context may lead to different effects of hydroperiod, and hydroperiod alone can only partly explain the variation on tadpole shape.

Environmental heterogeneity drives macrophyte beta diversity patterns in permanent and temporary ponds in an agricultural landscape

Understanding patterns of beta diversity (heterogeneity) and its components (substitution and subset) is important for managing freshwater ecosystems and the research on these topics has increased over the last decade. However, there has been limited empirical research exploring the drivers of these components of beta diversity in ponds from agricultural landscapes, in which hydroperiod length is often a key structural driver. The purpose of our work was to examine the contribution of substitution (species replacement among sites without changes in richness) and subset (species differences among sites when species-poor sites constitute subsets of those with a greater number of taxa) structuring processes on macrophyte beta diversity patterns of sixteen permanent and ten temporary Mediterranean ponds. We also aimed to test the structuring role of local environmental factors and geographic isolation and to determine whether there are differences in the community heterogeneity and the relative importance of the substitution and subset fractions of beta diversity between permanent and temporary ponds. We found that temporary ponds were environmentally and biologically less heterogeneous and supported lower richness than permanent waterbodies. In both pond types, beta diversity almost entirely reflected patterns of species substitution rather than subsets. Local environmental conditions, and not among-pond distance, were the main drivers of macrophyte community structure. Overall, our results suggest that local environmental variables operating through niche processes were the primary mechanisms driving macrophyte beta diversity patterns, thus highlighting the importance of environmental heterogeneity for maintaining pond community diversity in agricultural landscapes. Accordingly, conservation initiatives and ecosystem management strategies should include permanent and temporary pond clusters comprising wide environmental gradients in their efforts to ensure high levels of regional biodiversity.

Warming interacts with inundation timing to influence the species composition of California vernal pool communities

Climate change has been associated with alterations in temperature and precipitation regimes. Increased temperatures can change the structure and function of aquatic communities through both biotic and abiotic interactions. Many warming experiments have been conducted in permanent freshwater systems, but few in temporary freshwater systems that are dependent on precipitation patterns. Temporary aquatic communities are influenced by hydro-regime characteristics such as the hydroperiod length, magnitude, frequency, and timing of inundation, which may interact with temperature changes. Here, we used mesocosms to test for the effects of warming and inundation timing on the community composition of California vernal pools. California vernal pools are temporary wetlands, which provide habitat for many endemic and endangered species during the aquatic phase. Total species abundance was higher in both warm and late inundation treatments, while higher species richness levels in late treatments were due to the rapid emergence and colonization of species compared to early treatments. Heating increased the abundance of ubiquitous passive and active dispersers, including mosquitos, but decreased the abundance of vernal pool endemic passive dispersers. We also found that significant interactive effects between warming and inundation timing led to differences in community composition. These findings suggest that vernal pool endemic passive disperser species may decline due to increased temperatures and later inundation; however, the extent of such risk will likely be influenced by species-specific life-history traits such as bet-hedging strategies. Conservation efforts should work to identify the species most at risk to a changing climate.

Key environmental factors for the conservation of large branchiopods in farmland vernal pools — a case from a Central European diversity hotspot

Abstract Large branchiopod crustaceans are among the most threatened freshwater invertebrates of the world. They are regarded as a flagship group in the conservation of temporary waters, and knowledge of their ecology and conservation has developed rapidly in recent years, especially in the Mediterranean region. Little is known, however, about population functioning in species associated with vernal pools in cooler temperate areas, despite recent data showing a significant decline in their localities. The present study was conducted in western Poland, on a cluster of vernal pools known to host a Central European diversity hotspot of large branchiopods. We collected data on water and sediment quality, as well as hydroperiod length, to determine their effect on the occurrence of four large branchiopod species present in the ponds during our samplings: Eubranchipus grubii (Anostraca), Lynceus brachyurus (Laevicaudata), Cyzicus tetracerus (Spinicaudata) and Lepidurus apus (Notostraca). According to the statistical analyses, the presence or absence of particular species was affected by hydroperiod length, heavy metal content in the sediments of the marginal zone of the pond, total water phosphorus content, and pH value. Since previous studies show that deep and relatively small kettle-hole ponds seem to be the most vulnerable to human-induced changes in water nutrient contents and acidification, large branchiopod populations of this type of pools should be the first target for monitoring and active forms of protection, with the aim of maintaining the good water quality. Shallow shore-bursting type ponds are subject to increased heavy metal contamination and require activities reducing the influx of these elements from their agricultural catchment. Possible forms of protection are suggested, and the use of large branchiopods as an umbrella group in temporary waters of temperate climate is also discussed.

Hydroperiod length as key parameter controlling seed strategies in Mediterranean salt marshes: The case of Halopeplis amplexicaulis

The comprehension of plant biology and the response to the environment is fundamental to achieve the optimal skills to manage and conserve the fine equilibrium between biotic and abiotic parameters regulating natural biodiversity in salt marshes. The behaviour of annuals living in these stressful conditions is poorly understood and constitutes a good model for a better understanding of this relationship. We thus identified the determinant environmental factors involved in population survival of Halopeplis amplexicaulis, a threatened annual species inhabiting salt marshes. To achieve this objective, maternal climatic parameters were analyzed in seeds collected in different years, and correlated to seed dimensions (length, width and length/width ratio) and mass, and also to germination responses of the next generation. Our results proved a direct correlation between seed factors and the maternal environment determining the hydroperiod length, particularly autumn and winter temperatures, responsible of life cycle extent. Population survival is ensured by a narrow adaptation to climatic conditions through a natural halopriming of seeds. The combination of the two complementary germination strategies verified (opportunistic vs. bet-hedging) depending on the climatic conditions of the ripening year, is revealed as a density regulation mechanism controlling seed bank dynamics.

Simulated drought regimes reveal community resilience and hydrological thresholds for altered decomposition.

Future climate scenarios forecast a 10-50% decline in rainfall in Eastern Amazonia. Altered precipitation patterns may change important ecosystem functions like decomposition through either changes in physical and chemical processes or shifts in the activity and/or composition of species. We experimentally manipulated hydroperiods (length of wet:dry cycles) in a tank bromeliad ecosystem to examine impacts on leaf litter decomposition. Gross loss of litter mass over 112days was greatest in continuously submersed litter, lowest in continuously dry litter, and intermediate over a range of hydroperiods ranging from eight cycles of 7 wet:7 dry days to one cycle of 56 wet:56 dry days. The resilience of litter mass loss to hydroperiod length is due to a shift from biologically assisted decomposition (mostly microbial) at short wet:dry hydroperiods to physicochemical release of dissolved organic matter at longer wet:dry hydroperiods. Biologically assisted decomposition was maximized at wet:dry hydroperiods falling within the range of ambient conditions (12-22 consecutive dry days) but then declined under prolonged wet:dry hydroperiods (28 and 56 dry days. Fungal:bacterial ratios showed a similar pattern as biologically assisted decomposition to hydroperiod length. Our results suggest that microbial communities confer functional resilience to altered hydroperiod in tank bromeliad ecosystems. We predict a substantial decrease in biological activity relevant to decomposition under climate scenarios that increase consecutive dry days by 1.6- to 3.2-fold in our study area, whereas decreased frequency of dry periods will tend to increase the physicochemical component of decomposition.

The life cycle of the giant water bug of northwestern Patagonian wetlands: the effect of hydroperiod and temperature regime

AbstractWe analyzed the effect of hydroperiod and water temperature on the life cycle of the giant water bug Belostoma bifoveolatum in two wetlands of northwestern Patagonia, Argentina. In each wetland, we estimated adult and nymph abundance and monitored water depth and temperature throughout the study period. We determined the age structure of the giant water bug population in each wetland, and estimated the cumulative degree‐days (DD) needed for eggs to hatch and for nymphs to complete their development. Individuals of B. bifoveolatum colonized temporary wetlands at the beginning of spring when daylight lasts 12 h. The breeding period varied with hydroperiod length and showed both univoltine and bivoltine strategies, with a relatively constant breeding season. Egg‐bearing males appeared in October, carrying between 35 and 144 eggs per individual. Hatching success was high (~80% of eggs) and cumulative temperature for the hatching event was between 250 and 300 DD (which represents 3–4 weeks in nature), while complete development occurred between 800 and 1220 DD (~7–8 weeks). Individuals were more abundant in shallow and sunny patches of the wetlands, where the temperature was comparatively high, than in deeper or shaded sites. These results showed that hydroperiod duration and temperature could be good regulators of voltinism and development in B. bifoveolatum, driving the population structure of this giant water bug at the southern end of its distribution range.

Hierarchical procedure for creating local typologies for riparian zone research and management based on biophysical features

Riparian systems have been included as a key component in ecosystem management because of their role in buffering the impact of land-use activities on fluvial systems. Riparian knowledge can be enhanced with a typology that reflects the multiple relationships occurring throughout the landscape. We propose a hierarchical procedure based on biophysical aspects for building local to regional typologies for guiding research and management, using the Cuitzmala River Basin as a case study. The variables involved were obtained from geospatial databases, water balances, and topographic profiles. The levels and variables are context (altitude, geoform [mountains/hills/plains], and runoff coefficient), structure (stream order, longitudinal slope, hydroperiod, and segment length), and microstructure (lateral slope, bankfull width, and length-to-width ratio). We consider humidity and functional gradient along the basin to identify groups of streams and fluvial networks. Inside each network, we described structural and microstructural features associated with riparian functions, linking them with management decisions. Therefore, the proposed hierarchical procedure can help in making riparian heterogeneity visible, focusing research and management goals, and allowing the recognition of a spatial dimension of the processes being studied.

Effects of wetland hydroperiod length on the functional structure of assemblages of Odonata

AbstractThe role of hydroperiod as an environmental filter in structuring wetland assemblages is usually associated with trait selection in invertebrates. However, the effects of changes in the hydroperiod of non‐permanent wetlands on invertebrate assemblages are still unclear, and few studies have assessed the functional structure of insect assemblages along the hydroperiod gradient. In this study, we investigated the effects of different hydroperiod lengths on the functional structure of Odonata assemblages in non‐permanent wetlands (posteriorly classified as ‘short‐’, ‘medium‐’ and ‘long‐hydroperiod’) in southern Brazil in 2013 and 2014. Biological traits related to life‐history strategies in temporary waters were assessed according to seasonal patterns of occurrence of nymphal and adult stages of odonates. Following the rationale of an environmental filter produced by hydroperiod, we expected to find (1) higher functional diversity in longer hydroperiods and (2) trait‐convergence patterns in odonate assemblages in shorter hydroperiods. Patterns of functional diversity were detected along the hydroperiod gradient. More specifically, higher functional dispersion was found in long‐hydroperiod wetlands and trait‐convergence patterns occurred in wetlands with shorter hydroperiods, supporting our general hypothesis. Odonate taxa with life‐history traits associated with shorter life cycles predominated in medium‐ and short‐hydroperiod wetlands. Our results thus suggest that more pronounced reductions in wetland hydroperiod length should produce odonate assemblages functionally more similar, and these results gain special importance as climate change scenarios indicate that the hydrology of wetlands will be affected by variation in rainfall regimes.

Composition of cladoceran dormant stages in intermittent ponds with different hydroperiod lengths

AbstractDormancy is an adaptive mechanism found in cladoceran species to tolerate hydrologic fluctuations in temporary habitats. However, the effects of hydroperiod length on invertebrate community structure remain not fully understood. In this study, we conducted an experiment to assess changes in community structure of dormant stages of cladoceran species among ponds with different hydroperiods. Dry sediment samples were collected from intermittent ponds in southern Brazil, posteriorly assigned to three hydroperiod categories (long, medium and short). We tested for differences in the richness and composition of emerging cladoceran species along this hydroperiod gradient. Nine species emerged over the experiment, and cladoceran community structure changed among hydroperiods. Cladoceran richness was higher in medium‐ than in short‐ and long‐hydroperiod ponds. In addition, the composition of cladoceran species changed significantly between short‐ and long‐hydroperiod ponds. Our results indicated that changes in hydroperiod of intermittent ponds influenced the dormant stages of Cladocera, an important result regarding future predicted changes in hydric regime of freshwater ecosystems due to human‐induced climate change. We propose that desiccation‐resistant cladoceran species are likely to predominate and that richness of egg banks tends to be higher in ponds that hold water for periods shorter than 1 year.

Partitioning beta‐diversity through different pond hydroperiod lengths reveals predominance of nestedness in assemblages of immature odonates

AbstractPatterns of freshwater invertebrate assemblage structure in the transition from permanent to non‐permanent lentic habitats are well described in the literature. However, the effects of small changes in the hydroperiod of non‐permanent ponds on invertebrate assemblage structure remain less studied, especially on β‐diversity. Thus, we tested the effects of different pond hydroperiod lengths on the assemblage structure of immature odonates, in terms of both α‐ and β‐diversity. Small high‐altitude ponds with different hydroperiod lengths (assigned to ‘short’, ‘medium’ and ‘long’ hydroperiods) were sampled in southern Brazil between 2013 and 2014. Based on the hypothesis that shorter hydroperiods filter constituents of lentic fauna, i.e. that long‐living species cannot inhabit shorter‐hydroperiod ponds, we expected to find higher α‐ and β‐diversity in longer hydroperiods, as well as predominance of the nestedness component in β‐diversity. Restricted occurrence of some genera and higher α‐diversity of immature odonate assemblages was detected in long‐hydroperiod ponds. Within‐hydroperiod β‐diversity values did not vary among hydroperiods, because the occasional occurrence of some genera with high dispersal ability of adults in short‐hydroperiod ponds yielded similar values of the β‐diversity among hydroperiods. Partitioning of β‐diversity among hydroperiods revealed a significant higher contribution of the nestedness component rather than turnover. This pattern is explained by the occurrence of some generalist genera across the whole gradient of hydroperiod, as a subset of fauna in longer‐hydroperiod ponds. Thus, our results suggest that reduction in hydroperiod length, if occurring in the future climate change, would favor habitat‐generalist taxa in lentic ecosystems.