Pond Hydroperiod Research Articles

Managing invasive hybrids with pond hydroperiod manipulation in an endangered salamander system.

When invasive and endangered native taxa hybridize, the resulting admixture introduces novel conservation challenges. Across a large region of central California, a hybrid swarm consisting of admixed endangered California tiger salamanders (CTS) (Ambystoma californiense) and introduced barred tiger salamanders (BTS) (Ambystoma mavortium) has replaced native populations, threatening the genetic integrity of CTS and the vernal pool systems they inhabit. We employed a large-scale, genomically informed field experiment to test whether shortening breeding pond hydroperiod would favor native CTS genotypes. We constructed 14 large, seminatural ponds to evaluate the effect of hydroperiod duration on larval survival and mass at metamorphosis. We tracked changes in non-native allele frequencies with a 5237-gene exon capture array and employed a combination of custom Bayesian and generalized linear models to quantify the effect of pond duration on salamander fitness. Earlier work on this system showed hybrid superiority under many conditions and suggested that hybrids are favored in human-modified ponds with artificially long hydroperiods. Consistent with these earlier studies, we found overwhelming evidence for hybrid superiority. Very short hydroperiods substantially reduced the mass (1.1-1.5 fold) and survival probability (10-13 fold) of both native and hybrid larvae, confirming that hydroperiod likely exerts a strong selective pressure in the wild. We identified 86 genes, representing 1.8% of 4723 screened loci, that significantly responded to this hydroperiod-driven selection. In contrast to earlier work, under our more natural experimental conditions, native CTS survival and size at metamorphosis were always less than hybrids, suggesting that hydroperiod management alone will not shift selection to favor native larval genotypes. However, shortening pond hydroperiod may limit productivity of hybrid ponds, complementing other strategies to remove hybrids while maintaining vernal pool ecosystems. This study confirms and expands on previous work that highlights the importance of hydroperiod management to control invasive aquatic species.

Hydroperiod of temporary ponds threats amphibian recruitment in Mediterranean environments

Abstract Climate change threatens amphibians because they depend on water availability. The amount of time that a pond is filled with water – the hydroperiod – may play an important role in larval development and recruitment. Nevertheless it is usually not taken into account when predicting future species trends. We evaluated the role of the hydroperiod in the abundance of five amphibian species in temporal ponds of a Moroccan forest during a seven-year period. Particularly, we characterized the ponds and compared the climatic variables affecting our system with the previous eight-year period. We tested the relationship between rainfall and hydroperiod, and we identified the best predictor of amphibian abundance. Our data showed that the last seven years were drier than the previous eight, being three of them so dry that none of the amphibian species bred successfully in those seasons. We demonstrated that hydroperiod was the best predictor of the abundance of amphibian species and affected the amphibian community composition. The rainfall was correlated with the hydroperiod and the number of ponds filled. Species with long larval periods such as the endangered Moroccan spadefoot toad and the sharp ribbed newt might be more vulnerable to climate change since they need longer hydroperiods to develop. However, widespread species with shorter hydroperiods such as the Mauretanian toad or the stripeless tree frog might be favoured. In order to predict accurately amphibian species trend under climate change scenarios and to develop adequate conservation strategies, hydroperiod should be considered in both the models and mitigation actions.

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.

Extreme weather event disrupts reproduction of an isolated western spadefoot toad population, Pelobates cultripes (Cuvier, 1829), at its southern range limit

Pelobates cultripes can be considered among those amphibians most affected by climate change in Spain. Its long larval period and predicted shorter pond hydroperiods in its temporary breeding ponds may ultimately reduce population recruitment. We conducted surveys during its breeding season 2021–2022 in order to analyse one of the last remaining urban populations in its southern limit (coastal Malaga province). We recorded a decrease in rainfall and an increase in temperature compared to previous years. Although the species shortened its larval period in comparison with that previously reported, no post–metamorphic juveniles were observed. This interruption in reproduc tion highlights the need for improved monitoring of these isolated amphibian populations as it could be an early warning sign of global changes in the Mediterranean region.

Foreseen impact of climate change on temporary ponds located along a latitudinal gradient in Morocco

ABSTRACT Wetlands have been declining worldwide, with an estimated 64–71% loss over the last century. Climate change is increasing pressure on wetlands, affecting their hydrology, and Mediterranean temporary ponds could be particularly vulnerable to these changes. We studied the expected changes in hydrology and plant community according to climatic change scenarios in 18 temporary ponds distributed in 6 areas along a latitudinal and climatic gradient in Morocco (750 km; 4° latitudinal gradient). Richness of pond species was significantly correlated with water level and pond hydroperiod and showed a strong decline from north to south along with increased water stress. Using the Mar-O-Sel software (mar-o-sel.net), we simulated the future evolution of water balance and wetland hydroperiod (duration and frequency of flooding) in these ponds for mid- and late-21st century. Climate projections were estimated based on 2 Representative Concentration Pathway (RCP) scenarios assuming a stabilization (RCP4.5) or increase (RCP8.5) in greenhouse gas emissions. The mean water deficit of the ponds currently ranges between −1380 and −1812 mm/yr and would increase by 16–67% in 2100 under the RCP8.5 scenarios. Pond richness is expected to decrease by 8–15 species in 2100, depending on area, as a result of shorter projected hydroperiods. Severity of change was not related to location of the ponds along the latitudinal (aridity) gradient, but rather to the interaction between the size of their catchment area and the thickness of the permeable soil layer.

Increasing Hydroperiod in a Karst-depression Wetland Based on 165 Years of Simulated Daily Water Levels

The hydrology of seasonally inundated depression wetlands can be highly sensitive to climatic fluctuations. Hydroperiod—the number of days per year that a wetland is inundated—is often of primary ecological importance in these systems and can vary interannually depending on climate conditions. In this study we re-examined an existing hydrologic model to simulate daily water levels in Sinking Pond, a 35-hectare seasonally inundated karst-depression wetland in Tennessee, USA. We recalibrated the model using 22 years of climate and water-level observations and used the recalibrated model to reconstruct (hindcast) daily water levels over a 165-year period from 1855 to 2019. A trend analysis of the climatic data and reconstructed water levels over the hindcasting period indicated substantial increases in pond hydroperiod over time, apparently related to increasing regional precipitation. Wetland hydroperiod increased on average by 5.9 days per decade between 1920 and 2019, with a breakpoint around the year 1970. Hydroperiod changes of this magnitude may have profound consequences for wetland ecology, such as a transition from a forested wetland to a mostly open-water pond at the Sinking Pond site. More broadly, this study illustrates the needs for robust hydrologic models of depression wetlands and for consideration of model transferability in time (i.e., hindcasting and forecasting) under non-stationary hydroclimatic conditions. As climate change is expected to influence water cycles, hydrologic processes, and wetland ecohydrology in the coming decades, hydrologic model projections may become increasingly important to detect, anticipate, and potentially mitigate ecological impacts in depression wetland ecosystems.

Biogeochemical characteristics and hydroperiod affect carbon dioxide flux rates from exposed high‐elevation pond sediments

AbstractWhile inundated, small ponds (< 1000 m2 area) account for disproportionately large contributions of CO2 efflux to the global carbon budget and also store carbon in anoxic sediments. However, pond hydrology is shifting toward increasingly dry conditions in alpine and temperate zones, which might lead to increased exposure of shallow pond sediments. We analyzed sediment CO2 efflux rates in dried sediments of multiple ponds of varying hydrology and sediment characteristics at montane and subalpine elevations near the Rocky Mountain Biological Laboratory in Colorado. Average CO2 efflux rates from exposed sediments, 331.5 ± 11.5 mmol m−2 d−1 at the montane sites and 142.8 ± 45.1 mmol m−2 d−1 at the subalpine sites, were 10 times higher than average CO2 efflux rates from pond water. Principal components analysis to reduce dimensionality of sediment characteristics revealed that random inter‐pond differences rather than exposure timing or hydroperiod drove variation among sediments. In linear mixed effects models of CO2 flux rates, significant predictors included sediment moisture and temperature, pH, total organic carbon, and organic matter content at all pond hydroperiod classifications and sites. However, the sediment characteristics explaining the most variance differed among sites and hydroperiods and included nitrate concentrations, pH, bulk density, and temperature. We conclude that pond sediments are heterogeneous both within and among ponds in close proximity, and drivers of relatively high CO2 efflux rates differ among pond hydroperiods and elevations. This work emphasizes that local differences can impact predictions of CO2 flux from lentic sediments which are becoming increasingly exposed.

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.

Informing Amphibian Conservation Efforts with Abundance-Based Metapopulation Models

Science-based management strategies are needed to halt or reverse the global decline of amphibians. In many cases, sound management requires reliable models built using monitoring data. Historically, monitoring and statistical modeling efforts have focused on estimating occupancy using detection–nondetection data. Spatial occupancy models are useful for studying colonization–extinction dynamics, but richer insights can be gained from estimating abundance and density-dependent demographic rates. We developed an integrated abundance-based metapopulation model of the processes contributing to spatiotemporal variation in patch population density. We fit our model to a combination of detection–nondetection and count data from a 14-yr study of a reintroduced metapopulation of federally threatened Chiricahua Leopard Frogs (Lithobates chiricahuensis). Pond-specific population growth rate was influenced by pond hydroperiod and frog density, such that permanent and semipermanent ponds with low densities of adult frogs experienced the highest annual population growth rates. Immigration rate declined as the distance among ponds increased. After reintroduction in 2003, metapopulation-level abundance increased and appeared to stabilize around 1300 adult frogs (95% CI = 1192–1471) by year 2015. Further, changes in metapopulation abundance were driven mostly by changes in abundance at a few ponds. These high-density populations, which would not have been identifiable with traditional occupancy-based metapopulation models, are likely especially important for species recovery in the area. Abundance-based metapopulation models can be widely applied to inform conservation efforts, by providing higher quality information needed to prioritize habitat patches for management and can be used to make more accurate predictions of metapopulation extinction risk.

Carbon Dioxide Concentrations and Efflux from Permanent, Semi-Permanent, and Temporary Subalpine Ponds

Small ponds account for a disproportionately high percentage of carbon dioxide emissions relative to their small surface area. It is therefore crucial to understand carbon flow in these ponds to refine the current global carbon budget, especially because climate change is affecting pond hydrology. High elevation ponds in the Elk Mountains of western Colorado are drying more frequently as the timing of snowmelt advances. We compared CO2 concentrations and fluxes among ponds of different hydroperiods over diel sampling periods during the course of the 2017 open-water period. CO2 concentrations were significantly negatively correlated with pond depth and averaged 77.6 ± 24.5 μmol L−1 (mean ± S.E.) across all ponds and sampling events. Ponds were up to twenty times supersaturated in CO2 with respect to the atmosphere. Flux was highly variable within individual ponds but correlated with time of sampling and was highest at night. Flux averaged 19.7 ± 18.8 mg CO2 m−2 h−1 across all ponds and sampling events. We also compared flux values obtained using modeled and empirical methods and found that widely-applied models of gas exchange rates using wind-based gas exchange (K) values yielded estimates of CO2 flux that were significantly higher than those obtained using the floating chamber approach, but estimates of CO2 flux using globally averaged convection-based K values were lower than those obtained using the floating chambers. Lastly, we integrated soil vs. water efflux measurements with long-term patterns in hydrology to predict how total season-long efflux might change under the more rapid drying regimes and longer seasons that are already occurring in these systems. Because soil CO2 efflux averaged 277.0 ± 49.0 mg CO2 m−2 h−1, temporary ponds emitted 674.1 ± 99.4 kg CO2 m−2 over the course of the 2017 season from ice-out to refreezing, which was over twice as much as permanent and semi-permanent ponds. Our results emphasize that contributions of CO2 from small ponds to the global carbon budget estimates will vary with pond hydroperiod and sampling methodology, which have been overlooked given that most previous estimates were collected from limited sampling periods and from pond waters alone. Furthermore, pond CO2 contributions are predicted to increase over time as pond areas transition from efflux from water to efflux from soil.

The impact of phenology on the interaction between a predaceous aquatic insect and larval amphibians in seasonal ponds

Phenology has an important effect on the life strategies of species that live in temporary waters. Predaceous aquatic insects are key components of communities associated with seasonal ponds. Since the life cycles of these predators and their prey are unusual in that they occur at different moments of the pond hydroperiod, differences in temporal overlap could change the strength of their interactions. This study analyzed the phenology of the giant water bug Belostoma bifoveolatum and its prey. Breeding phenology, nymph population, and prey phenology were studied extensively in three wetlands during the spring season. Experimental trials were carried out to evaluate prey consumption and prey preference. The results showed a strong overlap in phenology between the water bug and the Pleurodema thaul frog. The timing of tadpole and water bug nymph hatching could ensure high survival levels of the early immature stages of this insect. As giant water bugs develop, their prey selectivity experiences a shift—older nymphs and adults having a higher impact on tadpoles. The fluctuating climate of the Patagonian region probably influences the phenology of predator–prey assemblages in seasonal communities, and may have the potential to drive feeding performance and the strength of interspecific interactions.

Partitioning tadpole beta diversity in highland ponds with different hydroperiods

Pond hydroperiod and other aspects of environmental heterogeneity play important roles in metacommunity organization in freshwater systems. We examined tadpole species richness and dissimilarities among assemblages at different hydroperiods (3, 7, and 13 mo) in highland ponds in the Araucaria moist forest ecoregion of southern Brazil. We also investigated whether β diversity components changed in accordance with spatial and environmental factors. We sampled tadpoles at 18 ponds between September 2012 and April 2013. Tadpole species richness was lower in permanent than in temporary ponds, but pond hydroperiod was not associated with tadpole abundance and species dissimilarities. β diversity was almost completely caused by species replacement associated with pond area, presence of predatory fish, and type of margin. Despite its small contribution, the nestedness component was associated with water depth and geographic patterns. Our study suggests that tadpole communities in the highlands of Araucaria moist forests are niche structured.

3. Local and Landscape-Scale Variables Influencing the Use of Ponds by Wood Frogs (Lithobates sylvaticus) in the Shakwak Valley, Yukon

A global decline in amphibian population numbers has generated a large body of research focused on amphibian habitat selection and species diversity conservation. The purpose of this study was to analyze the significance of both local and landscape-scale variables on wood frog (Lithobates sylvaticus) pond habitat selection in the Shakwak Trench in Yukon, Canada. Presence or absence of wood frogs was used to determine pond occurrence values for 40 different ponds. Independent local variables were collected in the field and through the use of Geographic Information Systems (GIS). Landscape variables were derived with GIS and were analyzed under a 1000m buffer around the perimeter of the study ponds. Pond perimeter and dominant perimeter vegetation were significant local variables. Small ponds with a dominant sedge vegetation types seemed to be selected over larger ponds. Large lake area in the landscape buffers had a significant negative relationship for wood frog habitat selection. Significant variables in this study are similar to those in previous studies or can be linked to other important variables such as pond hydroperiod and total forested area. Results should be considered to act as preliminary findings in a much more comprehensive and complete future amphibian habitat selection study of the area.

Continuous Hydrologic and Water Quality Monitoring of Vernal Ponds.

Vernal ponds, also referred to as vernal pools, provide critical ecosystem services and habitat for a variety of threatened and endangered species. However, they are vulnerable parts of the landscapes that are often poorly understood and understudied. Land use and management practices, as well as climate change are thought to be a contribution to the global amphibian decline. However, more research is needed to understand the extent of these impacts. Here, we present methodology for characterizing a vernal pond's morphology and detail a monitoring station that can be used to collect water quantity and quality data over the duration of a vernal pond's hydroperiod. We provide methodology for how to conduct field surveys to characterize the morphology and develop stage-storage curves for a vernal pond. Additionally, we provide methodology for monitoring the water level, temperature, pH, oxidation-reduction potential, dissolved oxygen, and electrical conductivity of water in a vernal pond, as well as monitoring rainfall data. This information can be used to better quantify the ecosystem services that vernal ponds provide and the impacts of anthropogenic activities on their ability to provide these services.

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.

Local and Landscape Drivers of Pond-Breeding Amphibian Diversity at the Northern Edge of the Mediterranean

Abstract: Most amphibian species are highly dependent on available aquatic habitats and their surrounding environments. In this study, we determined which factors influence amphibian diversity in a Mediterranean ecosystem characterized by a mosaic of natural areas and traditional land use. We sampled 60 temporary and permanent ponds in northeastern Portugal, determining amphibian species richness and community composition. At local (5- and 50-m buffers) and landscape (500-m buffer) scales, we analyzed the relationship between these measures and environmental factors describing wetland characteristics, surrounding land cover, habitat heterogeneity, and local road density. Both species richness and community composition were mainly influenced by local factors. Species richness was positively correlated with pond hydroperiod, habitat heterogeneity, and scrub cover within 5 m, and negatively correlated with bare ground coverage and road density within 50 m. Coniferous forest was the only landscape variable ex...

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.

Susceptibility to acidification of groundwater-dependent wetlands affected by water level declines, and potential risk to an early-breeding amphibian species

Eggs of the Western spadefoot toad (Pelobates cultripes) reached a 100% mortality in all 29 clutches deposited at a pH below 5.0 in a temporary pond of the Doñana National Park (SW Spain) throughout the wet season of 2006–2007. A similar trend was detected in a neighbouring pond. The proximity of these two ponds to a groundwater pumping area (<1.5km), prompted us to elucidate the possible links between the reduction in pond hydroperiod over past decades (1989–2008) and the decrease of groundwater pH-buffering capacity. The average hydroperiod had decreased by 4months since 1998–99 in the pond where the extensive egg mortality had occurred. The total alkalinity, and the Mg2+concentration had also significantly declined in the shallow water-table since 1998–99, from an average of 8.56 to 0.32meql−1, and of 3.57 to 1.15meql−1, respectively. This decline of the shallow groundwater buffering capacity could turn this pond more susceptible to the inorganic acidity associated with pyrite oxidation as the sediment S content was often above 0.03%. The initial ratio of S/Ca+Mg in the summer dry sediment was a good predictor of pore-water pH on re-wetting after desiccation (r2=0.802, p<0.01). Therefore, this ratio can give some anticipation to mitigate the impact of acidity on toad hatching before these temporary ponds are reflooded on the next wet season. Our results suggest that the long-term damage to pond water levels can trigger a potential risk of soil acidification in the presence of iron-sulphide minerals.

The Effects of Pond Drying and Predation on Blanchard's Cricket Frogs (Acris blanchardi)

Pond hydroperiod and predators play a central role in structuring aquatic communities. Because of predicted changes in precipitation and temperature patterns associated with climate change, pond hydroperiods will likely be altered. Reduced hydroperiods can impact amphibian populations by restricting the amount of time available for larval growth and by altering predatory interactions via increased predator densities. We investigated how pond drying and predation singularly and interactively affected growth and survival of Acris blanchardi (Blanchard's Cricket Frogs). We reared recently hatched tadpoles through metamorphosis in outdoor mesocosms using a factorial design incorporating three hydroperiods (fast-drying, slow-drying, or constant) and three larval odonate predator treatments (caged, uncaged, or absent). Caged and uncaged predator treatments were implemented to evaluate both consumptive and non-consumptive effects. There were no differences in survival, time to metamorphosis, or size at metamorph...

Larval development and growth ratios of Odonata of the Azores

To fully understand odonate life cycles, it is vital to analyse the patterns of larval growth, which are tightly associated with variations in environmental factors. However, the identification of larval instars is often difficult, especially for early development stages. We hypothesise that pond hydroperiod influences odonate larval growth, and test this idea with novel information about the environmental characteristics of 12 study ponds in Terceira Island (Azores). This study, which represents the first analysis of larval development of Odonata in the Azores, involved determining the instars of development and growth ratios. We measured the morphological characteristics of 898 Odonata larvae, and found that they significantly differed between temporary and permanent ponds. To estimate the larval instars, we used two methods: frequency distribution methods and correlation diagrams between body characteristics. The first method was the most effective, allowing the estimation of 17 instars for Anax imperator, 13 for Sympetrum fonscolombii and 10 for Ischnura hastata, as well as growth ratios between instars for head width, total length, abdomen length, wings and antenna length. Our results also suggest that a combination of the two methods is the most appropriate strategy for estimating the number of instars and growth ratios during larval development.