The influence of predator regime on reproductive traits in <Emphasis Type="Italic">Gammarus</Emphasis> <Emphasis Type="Italic">pulex</Emphasis> populations

Selection on traits conferring reduced predation may be opposed by selection on other traits associated with reproduction. Here, we examined the hypothesis that traits associated with reproduction in Gammarus pulex are driven by predation. We studied G. pulex originating from ponds with two different kinds of predator regimes: (1) ponds with fish—often large, non-gap-limited predators and (2) ponds without fish where invertebrates are the dominant predators—often small, gap-limited predators with a much more restricted prey size range. We examined the body size of males and females in G. pulex amplexus pairs originating from fish and fishless ponds. We also examined, in the laboratory, their mating success, the number of offspring per female and offspring mortality under different rearing conditions, with or without fish cue. Mating success, defined as the percentage of amplexus pairs that produced live offspring, was higher for G. pulex from fishless ponds independent of rearing condition. Individuals from fish ponds were larger and they produced a higher number of offspring which tended to be related to female body size. Offspring mortality was higher in populations from fish ponds compared to populations from fishless ponds. Despite the higher offspring mortality, females from fish ponds had a higher number of offspring alive after 13 weeks, which is the approximate time it takes for G. pulex to reach maturity. Our data imply that no trade-off between reducing body size to reduce mortality caused by fish and maximising reproductive success exist in G. pulex from fish ponds. The strategy with many offspring may be the correct strategy in fishponds where predation pressure generally is higher than in fishless ponds.     

Zooplankton of Fishless Ponds of Northern Patagonia: Insights into Predation Effects of Mesostoma ehrenbergii

The turbellarian predator Mesostoma ehrenbergii, a common inhabitant of fishless ponds of northern Patagonia, can consume prey larger than 1 mm. Because the feeding strategy of M. ehrenbergii includes mucus trapping and external digestion, this predator may exploit a broad range of prey sizes. We hypothesize that M. ehrenbergii could exert a strong effect on zooplankton composition and body size spectra in Patagonian fishless ponds. We investigated this hypothesis by analyzing the crustacean zooplankton composition and size spectra in five fishless ponds of northern Patagonia, and we carried out experiments to assess predation rates of M. ehrenbergii on potential prey species from 0.8 mm to 6 mm. These ponds were colonized by macrophytes, which favored habitat heterogeneity, especially in the smaller ponds that had higher species richness. The surveyed ponds showed distinctive crustacean zooplankton assemblages and sizes, but all were dominated by calanoid copepods of the genus Boeckella. Our results indicated that M. ehrenbergii consumed the whole size range of offered prey, from ∼0.8 mm (Ceriodaphnia dubia) to ∼6 mm (Parabroteas sarsi). Predation rates were higher for intermediate‐bodied copepods (∼1.5 mm) and C. dubia (0.8 mm), but we did not find conclusive evidence that variations in size spectra of crustacean zooplankton are a result of M. ehrenbergii predation. We suggest that an interaction between prey body size and its evasion tactic might be important to determine the true effect Mesostoma on zooplankters. The structural complexity created by macrophytes in Patagonian fishless ponds may also help account for the lack of a strong predation effect of Mesostoma in the field survey. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Plasticity or fixed adaptive traits? Strategies for predation avoidance in Rana arvalis tadpoles

Tadpoles of Rana arvalis originating from seven island populations were tested for responses to non-lethal predator presence. In general, tadpole growth was reduced and the relative tail depth was increased at predator presence. There was no effect of predator presence on the predicted size at metamorphosis. The differentiation rate, translating as length of the larval period, was lower at predator presence, but this seems to be merely an effect of the reduced growth. Although populations differed with respect to growth, relative tail length, relative tail depth, differentiation rate and predicted size at metamorphosis, no obvious differences were found in their responses to predator presence. Data on predator occurrences in the source ponds show that tadpoles originating from ponds with a high predation pressure have a higher differentiation rate, i.e. they will metamorphose at an earlier date than those from “safe” ponds (if raised under the same conditions). Moreover, they are also predicted to metamorphose at a smaller size, which is in accordance with theoretical models. Despite the fact that populations differed in growth, no correlation was found between growth and predation risk in the source ponds. Received: 16 March 1998 / Accepted: 18 July 1998     

EVOLUTION OF GIGANTISM IN NINE‐SPINED STICKLEBACKS

The relaxation of predation and interspecific competition are hypothesized to allow evolution toward “optimal” body size in island environments, resulting in the gigantism of small organisms. We tested this hypothesis by studying a small teleost (nine‐spined stickleback, Pungitius pungitius) from four marine and five lake (diverse fish community) and nine pond (impoverished fish community) populations. In line with theory, pond fish tended to be larger than their marine or lake conspecifics, sometimes reaching giant sizes. In two geographically independent cases when predatory fish had been introduced into ponds, fish were smaller than those in nearby ponds lacking predators. Pond fish were also smaller when found in sympatry with three‐spined stickleback (Gasterosteus aculeatus) than those in ponds lacking competitors. Size‐at‐age analyses demonstrated that larger size in ponds was achieved by both increased growth rates and extended longevity of pond fish. Results from a common garden experiment indicate that the growth differences had a genetic basis: pond fish developed two to three times higher body mass than marine fish during 36 weeks of growth under similar conditions. Hence, reduced risk of predation and interspecific competition appear to be chief forces driving insular body size evolution toward gigantism.     

Predation in a temporary pond with special attention to the trophic role of Triops cancriformis (Crustacea: Branchiopoda: Notostraca)

Temporary ponds are described as environments with a low predation pressure. Notostracans inhabit these types of ponds, and some populations acquire a high proportion of larger individuals, whose feeding behaviour is mainly predatory. The predation nature of Triops cancriformis is not widely accepted, because its diet is still partly controversial. We analysed the diet of one population of T. cancriformis in a Mediterranean temporary pond (Espolla pond, NE Iberian peninsula) to evaluate its predation behaviour. The gut content of the individuals bigger than 10 mm is mainly composed of detritus, plant fibres and microcrustaceans (cladocerans, ostracods and copepods). The prey number increases with the body size of individual T. cancriformis as previously described. Sex-biased predation was observed for one copepod prey, but not for the other. Predation pressure in that community was monitored along six hydroperiods as the percentage of predator biomass (not only T. cancriformis) in relation to the non-predator biomass. The proportion of predator biomass is high, and this contrasts with the low predation pressure expected for a temporary system with short hydroperiods.     

Effects of density and predation on Scaphiopus couchi tadpoles in desert ponds

Summary The effects of density on growth and development of Scaphiopus couchi tadpoles in desert ponds were investigated, and sources of mortality over a three-year period were documented. In 16 of the 82 ponds monitored, predation was the principal cause of death, demonstrating that tadpoles in desert ponds may be exposed to high levels of predation, although the overall importance of predation is less here than in more mesic areas. Desiccation was the primary cause of mortality in 49 ponds. Growth and development were extremely slow in most high density ponds and as a result most tadpoles were unable to metamorphose before ponds dried. Only 8 ponds produced metamorphs, and mortality was high even in these. Food-supplementation resulted in some metamorphosis in high density ponds, although the effect was diminished by the extreme crowding in most ponds. In low density ponds, S. couchi tadpoles can develop very quickly and metamorphose. High mortality due to desiccation is largely a consequence of high density: tadpoles rarely completed development in high density ponds, regardless of pond duration.     

Body size determines eyespot size and presence in coral reef fishes

Numerous organisms display conspicuous eyespots. These eye‐like patterns have been shown to effectively reduce predation by either deflecting strikes away from nonvital organs or by intimidating potential predators. While investigated extensively in terrestrial systems, determining what factors shape eyespot form in colorful coral reef fishes remains less well known. Using a broadscale approach we ask: How does the size of the eyespot relate to the actual eye, and at what size during ontogeny are eyespots acquired or lost? We utilized publicly available images to generate a dataset of 167 eyespot‐bearing reef fish species. We measured multiple features relating to the size of the fish, its eye, and the size of its eyespot. In reef fishes, the area of the eyespot closely matches that of the real eye; however, the eyespots “pupil” is nearly four times larger than the real pupil. Eyespots appear at about 20 mm standard length. However, there is a marked decrease in the presence of eyespots in fishes above 48 mm standard length; a size which is tightly correlated with significant decreases in documented mortality rates. Above 75–85 mm, the cost of eyespots appears to outweigh their benefit. Our results identify a “size window” for eyespots in coral reef fishes, which suggests that eyespot use is strictly body size‐dependent within this group.     

The influence of climate change scenarios on populations of the mayfly Cloeon dipterum

Populations of the mayfly Cloeon dipterum from 48 ponds (3000 l fibre-glass tanks of 1 m depth) were monitored over the course of 1 year. To simulate possible patterns of climatic change, the ponds were subject to three temperature treatments: continuous heating to 3 °C above ambient; heating to 3 °C above ambient during the summer only; and no heating. Further experimental complexity included enhanced nutrient input into the ponds and the presence or absence of fish, giving a factorial combination of 3 temperature regimes × 2 nutrient levels × presence/absence of fish predation.Few nymphs were found in the presence of fish. Where fish were absent, the temperature treatments did not significantly affect nymph abundances, and only marginally influenced mean nymph body-lengths. In contrast, the nutrient treatment had significant effects on both nymph abundance and size, with greater numbers of generally larger nymphs occurring in those fish-free ponds receiving additional nutrients. Adult emergence began earlier in the year from the heated ponds, particularly those ponds receiving additional nutrients. Adult body-length differed between temperature treatments, but consistent patterns were difficult to ascertain because of interactions with nutrient treatment and seasonal effects.Our results show that during the short term at least, elevated temperature as a simulation of climate change does not have an overwhelming influence on either mayfly abundance or size. The influence of temperature is subtle and subject to complex interaction with other habitat variables. We therefore suggest that the direct consequences of small changes in temperature will likely be of little significance to C. dipterum, relative to indirect effects operating through interactions with predation and nutrient input.     

CYTOLOGICAL AND PHYLOGENETIC DIVERSITY IN FRESHWATER ESOPTRODINIUM/BERNARDINIUM SPECIES (DINOPHYCEAE)1

The genera Esoptrodinium Javornický and Bernardinium Chodat comprise freshwater, athecate dinoflagellates with an incomplete cingulum but differing reports regarding cingulum orientation and the presence of chloroplasts and an eyespot. To examine this reported diversity, six isolates were collected from different freshwater ponds and brought into clonal culture. The isolates were examined using LM to determine major cytological differences, and rDNA sequences were compared to determine relatedness and overall phylogenetic position within the dinoflagellates. All isolates were athecate with a left‐oriented cingulum that did not fully encircle the cell, corresponding to the current taxonomic concept of Esoptrodinium. However, consistent cytological differences were observed among clonal isolates. Most isolates exhibited unambiguous pale green chloroplasts and a distinct bright‐red eyespot located at the base of the longitudinal flagellum. However, one isolate had cryptic chloroplasts that were difficult to observe using LM, and another had an eyespot that was so reduced as to be almost undetectable. Another isolate lacked visible chloroplasts but did possess the characteristic eyespot. Nuclear rDNA phylogenies strongly supported a monophyletic Esoptrodinium clade containing all isolates from this study together with a previous sequence from Portugal, within the Tovelliaceae. Esoptrodinium subclades were largely correlated with cytological differences, and the data suggested that independent chloroplast and eyespot reduction and/or loss may have occurred within this taxon. Overall, the isolates encompassed the majority of cytological diversity reported in previous observations of Bernardinium/Esoptrodinium in field samples. Systematic issues with the current taxonomic distinction between Bernardinium and Esoptrodinium are discussed.     

Spatial dependence of phenotype-environment associations for tadpoles in natural ponds

Within natural habitats, phenotypes are shaped by many environmental factors. Consequently, heterogeneity of these factors can promote phenotypic divergence. However, because environments exhibit heterogeneity at different spatial scales, phenotypic divergence should also exhibit such scale-dependence. Using hierarchical linear models, I determined how multiple environmental factors at two spatial scales affected the morphology of wood frog (Rana (Lithobates) sylvatica) tadpoles collected from natural ponds. Among ponds, predation risk intensity and tadpole density were strong predictors of tadpole morphology, while within ponds, other environmental variables such as water depth and leaf litter were more important. Spatial analyses revealed that water depth and leaf litter, but not predation risk intensity or tadpole density, exhibited heterogeneous spatial distributions within ponds, suggesting that spatial properties of environmental variables influenced the scale at which they shaped phenotypes. Furthermore, patterns of phenotypic variation with respect to predation risk intensity and tadpole density among ponds largely matched observations from previous laboratory studies. These results emphasize the importance of considering phenotype-environment associations across multiple spatial scales.     

Zooplankton community structure driven by vertebrate and invertebrate predators

Summary A zooplankton community was established in outdoor experimental ponds, into which a vertebrate predator (topmouth gudgeon: Pseudorasbora parva) and/or an invertebrate predator (phantom midge larva: Chaoborus flavicans) were introduced and their predation effects on the zooplankton community structure were evaluated. In the ponds which had Chaoborus but not fish, small- and medium-sized cladocerans and calanoid copepods were eliminated while rotifers became abundant. A large-sized cladoceran Daphnia longispina, whose juveniles had high helmets and long tailspines as anti-predator devices, escaped from Chaoborus predation and increased. In the ponds which had fish but not Chaoborus, the large-sized Daphnia was selectively predated by the fish while small-and medium-sized cladocerans and calanoid copepods predominated. In the ponds containing both Chaoborus and fish, the fish reduced the late instar larvae (III and IV) of Chaoborus but increased the early instar larvae (I and II). Small- and large-sized cladocerans were scarcely found. The former might have been eliminated by predation of the early instar larvae of Chaoborus, while the latter was probably predated by fish. Consequently, the medium-sized cladocerans, which may have succeeded in escaping from both types of predator, appeared abundantly. The results suggest that various combinations of vertebrate and invertebrate predators are able to drive various kinds of zooplankton community structure.     

Size-selective and sex-selective predation by brown bears on sockeye salmon

Breeding activity increases the vulnerability of many animals to predation, and such predation can affect the subset of animals successfully reproducing. To study the ways in which predation might affect the evolution of Pacific salmon, we measured the intensity and selectivity of predation by bears (primarily brown bears, Ursus arctos) on mature sockeye salmon (Oncorhynchus nerka) breeding in a series of small, spring-fed ponds and creeks near Pedro Bay, Alaska, from 1994 to 1998. Bears killed male salmon more often than females; males constituted 60% of the kills but only 35% of the salmon that died of senescence. The bears also killed fish that were larger, on average, than those dying of senescence (males: 462 vs 452 mm; females: 453 vs 443 mm). The level of predation varied greatly, from 4% (females) and 10% (males) in 1994 to 100% of both sexes in 1996 and 1997. The rate of predation also varied among habitats, being lower in larger ponds than in smaller, shallower ponds and the very small interconnecting creeks. Despite the intense and size-selective predation, the salmon in safer habitats (large ponds) were not larger than those in riskier habitats, and salmon densities were only slightly higher in the safer areas. Compared to a nearby population that experiences no bear predation (Woody Island), the male sockeye salmon from the Pedro Pond system had shallower bodies (i.e., less exposure in shallow water) for a given length, consistent with the hypothesis that selective predation can affect the extent of sexual dimorphism among populations. However, the average length at age for both males and females was greater in the Pedro Pond fish, indicating that selective factors besides predation affect length. Overall, the results indicate that bears can be an agent of natural selection within (and perhaps between) sockeye salmon populations, and predation can greatly affect reproductive success among individuals and years for the population as a whole. Received: 6 April 1999 / Accepted: 1 June 1999     

Consequences of the size structure of fish populations for their effects on a generalist avian predator

Size-structured interspecific interactions can shift between predation and competition, depending on ontogenetic changes in size relationships. I examined the effects of common carp (Cyprinus carpio), an omnivorous fish, on the reproductive success of the red-necked grebe (Podiceps grisegena), an avian gape-limited predator, along a fish size gradient created by stocking distinct age-cohorts in seminatural ponds. Young-of-the-year (0+) carp were an essential food source for young grebes. Only adult birds were able to consume 1-year-old (1+) fish, while 2-year-old (2+) fish attained a size refuge from grebes. Amphibian larvae were the principal alternative prey to fish, followed by macroinvertebrates, but the abundance of both dramatically decreased along the carp size gradient. Fledging success was 2.8 times greater in ponds with 0+ versus 1+ carp; in ponds with 1+ carp, chicks received on average 2.6–3 times less prey biomass from their parents, and over 1/3 of broods suffered total failure. Breeding birds avoided settling on 2+ ponds. These results show that changes in prey fish size structure can account for shifts from positive trophic effects on the avian predator to a negative impact on the predator’s alternative resources. However, competition did not fully explain the decrease in grebe food resources in the presence of large fish, as carp and grebes overlapped little in diet. In experimental cages, 1+ carp totally eliminated young larvae of amphibians palatable to fish. In field conditions, breeding adults of palatable taxa avoided ponds with 1+ and older carp. Non-trophic interactions such as habitat selection by amphibians or macroinvertebrates to avoid large fish may provide an indirect mechanism strengthening the adverse bottom-up effects of fish on birds.     

Pond tadpoles with generalized morphology: is it time to reconsider their functional roles in aquatic communities?

With rare exceptions, anuran larvae have traditionally been considered to occupy lower trophic levels in aquatic communities where they function as microphagous suspension feeders. This view is being challenged by studies showing that tadpoles with generalized morphology often function as macrophagous predators. Here, we review the literature concerning macrophagy by tadpoles and provide two additional examples involving generalized tadpoles. In the first, we demonstrate with laboratory and field experiments that wood frog (Rana sylvatica) tadpoles are major predators of macroinvertebrates in ponds. In the second, we show that green frog (R. clamitans) tadpoles can cause catastrophic reproductive failure of the wood frog via egg predation. These results and data from other studies challenge the assumption that generalized tadpoles function as filter-feeding omnivores, and question the general applicability of community organization models which assume that predation risk increases with pond permanence. We suggest that predation risk is greater in temporary ponds than in more permanent ponds for many organisms that are vulnerable to predation by tadpoles. This being so, a conditional model based upon interactions that are species-specific, life-stage-specific, and context-dependent may better explain community organization along hydrological gradients than models which assume that temporary ponds have few or no predators. Received: 30 November 1998 / Accepted: 2 May 1999     

Effects of pond size and consequent predator density on two species of tadpoles

Experimental ponds were used as a model system of habitat patches to study the effect of habitat size on the relative growth performance of tadpoles of Bufo americanus and Pseudacris triseriata, and on colonization by predatory insects. Three pond depths and surface areas were habitat size treatments in a replicated, factorial experiment. Tadpoles of both species were astablished together at a single density and ponds were left open to natural colonization by aquatic insects. Pond area had a significant effect on the multivariate response of P. triseriata larval period, survival, and metamorphic mass. P. triseriata survived better relative to B. americanus in larger ponds. However, increasing pond area led to greater incidence of predacious beetle larvae (Dytiscus, Coleoptera: Dytiscidae). Dytiscus larvae had a significant negative effect on the survival of P. triseriata and led to reduced P. triseriata survival relative to B. americanus in colonized ponds. The results suggest that habitat size can influence community structure by altering the distribution of predation among habitat patches.     

COSTS AND BENEFITS OF A PREDATOR-INDUCED POLYPHENISM IN THE GRAY TREEFROG HYLA CHRYSOSCELIS

The phenotypes of gray treefrog (Hyla chrysoscelis) tadpoles vary depending on whether predators are present in the pond. Tadpoles reared in ponds with predatory dragonfly larvae are relatively inactive compared with tadpoles in predator-free ponds, and have relatively large, brightly colored tailfins with dark spots along the margins. Models for the evolution of plasticity predict that induced phenotypes such as this should confer high fitness relative to the typical phenotype when in the presence of predators, but should be costly when the predator is absent. Our study tested for the predicted fitness trade-off in H. chrysoscelis by first rearing tadpoles in mesocosms under conditions that induce the alternate phenotypes, and then comparing the performance of both phenotypes in both environments. We generated the two phenotypes by rearing tadpoles in 600-liter outdoor artificial ponds that contained either two caged dragonflies (Anax junius) or an empty cage. Tadpoles from the two environments showed significantly different behavior, tail shape, and tail color within two weeks of exposure. We compared the growth and survival of both phenotypes over four weeks in ponds where there was no actual risk of predation. Under these conditions, both phenotypes grew at the same rate, but the predator-induced phenotype had significantly lower survival than the typical phenotype, indicating that induced tadpoles suffered greater mortality from causes other than odonate predation. We tested the susceptibility of both phenotypes to predation by exposing them to dragonflies in 24-h predation trials. The predator-induced phenotype showed a significant survival advantage in these trials. These results confirm that the predator-induced phenotype in H. chrysoscelis larvae is associated with fitness costs and benefits that explain why the defensive phenotype is induced rather than constitutive.     

The influence of flatworm predation on zooplankton inhabiting small ponds

Experiments were performed in 1977 to determine which large zooplankton in a series of high altitude ponds can be consumed by the predatory flatworm Mesostoma ehrenbergii. This predator consumes Daphnia at a high rate and the fairy shrimp Branchinecta at a low rate, but does not consume Diaptomus. Experiments were performed in 1978 and 1979 to determined the rate of predation on Daphnia in 30 liter tubs and to determine if predation rate is correlated with surface to volume ratio of experimental containers. There is a clear correlation between surface to volume ratio and predation rate. Determinations of Mesostoma and Daphnia densities were made in a series of eight high altitude ponds, and pond surface to volume ratios were determined. Examination of these parameters lends credence to the argument that Mesostoma predation affects Daphnia dynamics in some circumstances. The results suggest that benthic invertebrate predators may affect zooplankton dynamics, especially in shallow ponds.     

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.     

Better desiccated than eaten by fish: Distribution of anurans among habitats with different risks to offspring

1. Freshwater species with complex life cycles face a trade-off between the risks of offspring mortality due to desiccation in temporary habitats and due to predators common in long-duration habitats, especially fish. In real-world conditions, intermediate-gradient areas that are highly suitable for some ecological specialists are often limited. I examined the relative significance of drivers of the permanence–predation gradient in habitat selection by pond-breeding anurans.
2. Anuran oviposition was investigated at the community level in fish pond landscapes with only three types of habitat, permanent fish-containing ponds and highly desiccation-prone pools, either fishless or recently emptied of fish and with fish odour (fish cue). Altogether, 65 ponds/pools, interspersed in four clusters, were examined for the presence of egg masses.
3. Bufo bufo was the only species preferring permanent ponds. Egg masses of Rana sp. (Rana arvalis/Rana temporaria) occurred in all fishless pools, and less frequently in the ponds. Bufotes viridis and long larval period species Pelobates fuscus and Hyla orientalis oviposited almost exclusively in fishless pools. Fish-cue pools were avoided by all species. Anuran richness was higher in fishless pools than in permanent ponds. Species distribution between the two habitats was nested, with both common and rare species occurring in fishless pools.
4. The results indicate the primacy of offspring predation risk over hydroperiod constraints in oviposition decision-making by fish-intolerant anurans. The absence of some species from ponds and pools with fish or fish cues shows that non-consumptive interactions may better explain the scarcity of anuran larvae in waters dominated by fish than actual consumption. The strict avoidance of fish habitats despite their proximity to fishless patches indicates fine-scale assessment of predation risk. However, rigid habitat selection against fish predation on offspring may prove maladaptive if habitats with high desiccation risk are the main alternative and are indiscriminately preferred. Maintenance of fishless wetlands with a hydroperiod sufficient to allow completion of metamorphosis should be a conservation priority for anuran diversity in areas where fishless habitats are limited.

     

Percottus glehni Dybowski — a new colonizer in the ichthyofauna of Lake Glubokoe

Percottus glehni is a new colonizer in the ichthyofauna of Lake Glubokoe. Recently, this species, established in the European part of the USSR nearly 30 years ago, has become common in the lakes and ponds located 3–5 km from Lake Glubokoe. In Lake Glubokoe it keeps mainly to water thyme (Elodea) in shallow water with individuals up to 7 cm in size being predominant. Apparently, these fishes are not abundant due to strong predation pressure from larger predators.