Search

We experimentally tested whether the presence of a free benthic predator (Odonata naiads) alters the displacement time, the position occupied in the water column, and the proportion of food consumed by benthic and nektonic tadpoles. The presence of predators did not influence the displacement time or the proportion of food consumed by any of the two species. In the presence of predators, benthic tadpoles avoided the benthic microhabitat, increasing their time in the middle of the water column. This behavior was unexpected since the previous studies indicate that the morphology of benthic tadpoles restricts them to the bottom of water bodies. We, thus, hypothesize that such a drastic behavior change was a consequence of the real risk of predation to which the tadpoles were exposed. Our results are in accordance with the threat-sensitivity hypothesis, in which prey behave flexibly when exposed to different degrees of predation threats. Nektonic tadpoles, however, slightly increased their permanence in the water column in the presence of the same benthic predators. Therefore, we provide support for the hypothesis that predators induce greater behavioral changes in prey that exhibit patterns of microhabitat use similar to theirs. [ABSTRACT FROM AUTHOR]

This study explored how increased water turbidity in open-aquaculture ponds as a result of enhanced fertilization influences piscivorous bird assemblages and predation pressure on fish. Fertilization treatments were applied to 24 earth-bottom ponds, and bird assemblages, visitation frequencies, diversities and predation rate responses were compared at species richness and across four functional group scales during six months. Bird visitation frequency, species richness and functional diversity increased around unfertilized ponds, especially for large wading birds. Fertilization and bird species richness were each negatively related to bird predation rate, whereas functional diversity was positively associated with predation rate regardless of pond fertilization. Furthermore, predation rate reduced in response to pairwise interactive effects of fertilization and functional group identity, but increased with fertilization's respective interaction with functional diversity and visitation frequency. Contrastingly, species richness showed no interactive effect with fertilization or visitation rate. Thus, in applying enhanced pond water fertilization as a mitigation measure for controlling and tracking damage impact caused by piscivorous birds, it is potentially more beneficial to adopt a bird functional rather than species-based approach, given the observed higher sensitivity of functional diversity in predicting predation rates. The findings present novel, farmer-centered and affordable strategies for piscivorous problem-bird control toward sustainable aquaculture. [ABSTRACT FROM AUTHOR]

Mosquitoes transmit viruses that affect public health in tropical regions. Identifying factors that influence their fitness can help control mosquito-borne diseases. We investigated the impacts of predation risk effects, from a fish predator, and food availability on the oviposition behavior of Aedes aegypti. We hypothesize that predation risk and food availability interactively affect Ae. aegypti oviposition. Gravid Ae. aegypti females were offered oviposition sites with all possible combinations of predation risk (with vs. without predator cues) and food availability (low vs. high). We found a significant interaction between predation risk and food availability. The magnitude of oviposition and the probability of egg laying in high food availability treatments exceeded the values of low food availability treatments, but only in treatments without predation risk. Predation risk critically modulated the effects of food availability on the oviposition of Ae. aegypti. This study demonstrates the interplay between predation risk and food availability in controlling mosquito-borne diseases. [ABSTRACT FROM AUTHOR]

Understanding inter-annual variation in the density of young-of-the-year fish is an important tool for assessing stock status and guiding management decisions. We analyzed data spanning from 2003 to 2022 collected at Lipno Reservoir in Czechia. The study aimed to identify factors influencing the density of pikeperch (Sander lucioperca), a valuable predatory fish species in European waters. A bimodality test for the size class distribution has revealed the existence of two distinct YOY cohorts: extremely small (ES) and ordinary fingerlings. Using the Bayesian horseshoe prior method with 37 potential predictors, followed by linear regression, we observed that certain environmental factors similarly influenced both cohorts. Higher temperatures during spring and summer, coupled with increased densities of large and medium-sized cladocerans, positively affected the density of both cohorts. However, distinct influences were observed: for ordinary fingerlings, increased summer precipitation and a lower abundance of predators were beneficial, whereas, for ES fingerlings, summer copepod density emerged as an additional positive factor. This study emphasizes the importance of a detailed investigation of factors influencing pikeperch recruitment. Examining these drivers provides a clearer insight into the causes of variations in the early life stage, which is crucial for monitoring and managing populations in temperate reservoirs. [ABSTRACT FROM AUTHOR]

To test the hypotheses that multigenerational predation risk favors clones with longer postero-lateral spines and a larger body, and that fitness consequences of selection depend on both tested fitness variables and selection intensity, we expose replicate Brachionus dorcas populations in low (LK) and high (HK) concentrations of Asplanchna kairomones. Over 60 days (23 asexual generations) of selection, LK-selected populations showed the highest equilibrium population densities, and median mictic ratios and postero-lateral spine lengths, and HK-selected populations showed the lowest equilibrium population densities, the highest mictic ratios, and the longest postero-lateral spines, among all the control and treatment populations. In the absence of Asplanchna kairomones, and compared with populations with the control selection history, populations with an LK selection history showed increased growth rates/intrinsic rates of population increase and net reproductive rates, but decreased mictic ratios, indicating three fitness gains and a fitness cost; and those with an HK selection history showed increased life expectancy at hatching and mictic ratios, but decreased growth rates, indicating two fitness gains and a fitness cost. Asplanchna kairomones might increase the heritability of higher equilibrium densities or mictic ratios, and longer postero-lateral spines, and thus enable the prey to survive predation. [ABSTRACT FROM AUTHOR]

We quantified the effect of two cyclopoids, an invasive (Mesocyclops pehpeiensis) and a native (Mesocyclops longisetus curvatus) species on the population growth of the rotifers Brachionus havanaensis and Brachionus calyciflorus. We hypothesized that the invasive copepod would have a greater adverse effect on the test rotifers. The population growth of B. havanaensis was tested in the indirect presence of B. calyciflorus (used as prey for the predatory copepods), and the predatory copepods, M. pehpeiensis and M. longisetus curvatus. For B. calyciflorus the experimental design was as above except that we used B. havanaensis as prey. The test rotifers were separated from the competitors and predators by mesh cages placed in the experimental jars. Rotifer density and the egg ratios were quantified, followed by a daily medium change, until the population density declined. The population growth rate of B. havanaensis ranged between 0.26 and 0.30 day−1, while that of B. calyciflorus between 0.19 and 0.21 day−1. The presence of the invasive copepod had an adverse effect on the smaller (< 110 µm) B. havanaensis, but not on the larger (> 180 µm) B. calyciflorus. The results are discussed with emphasis on the differences in the indirect impact invasive and native predatory copepods. [ABSTRACT FROM AUTHOR]

We quantified the population growth of the predatory heliozoan Actinosphaerium eichhornii fed separately four rotifer prey (Anuraeopsis fissa, Brachionus calyciflorus, Brachionus havanaensis and Plationus patulus) at three densities (0.5, 1 and 2 ind. ml−1 per day). All the four prey rotifer species were consumed by A. eichhornii. Regardless of the prey species, increasing rotifer prey density resulted in an increased population growth of the heliozoans. Higher cyst production in A. eichhornii occurred at higher prey densities on all prey species. A. fissa offered at the lower densities of 0.5–1.0 ind. ml−1 day−1 did not lead to cyst production by A. eichhornii. The predator did not survive beyond 2 days on Chlorella vulgaris alone. When cultured together with heliozoans, A. fissa, B. calyciflorus and B. havanaensis were eliminated within 4 days. However, the prey rotifer Plationus patulus continued to survive for about 10 days with heliozoans. The highest rate of population increase of heliozoans (0.91 day−1) was recorded when fed B. calyciflorus at a density of 2 ind. ml−1 day−1, while of those of prey varied from 0.30 to 0.41 day−1 when fed Chlorella vulgaris at 1 × 106 cells ml−1 day−1. We have analyzed the impact of heliozoan predation on rotifers. [ABSTRACT FROM AUTHOR]

Predation is a well-known factor that structures rotifer communities. However, the role of protists as predators is relatively understudied. Here, we investigated predatory behavior of Actinosphaerium sp., a freshwater heliozoan, on seven rotifer species. Predators and prey were collected from a local playa; except for Brachionus calyciflorus that served as a naive prey control. Prey included large species (≥ 175 µm mean length: Asplanchna sieboldii, B. calyciflorus, Platyias quadricornis, and Lacinularia flosculosa) and small species (< 175 µm: Cephalodella gibba, Euchlanis dilatata, and Lepadella patella). Four experiments were conducted. (1) Single prey items of varying size and motility. Larger prey types were ~ 1.7 to 3.0 times more likely to be ingested than small prey. No L. flosculosa were ingested, contrary to field observations. No correlation was found between swimming speed and predation risk. (2) Preference tests. Asplanchna sieboldii and B. calyciflorus were favored prey. (3) Growth rate of Actinosphaerium on mixed diets, with and without Asplanchna. Highest population growth of Actinosphaerium was observed in presence of A. sieboldii. (4) Prey defenses. Susceptibility of spined versus unspined B. calyciflorus resulted in no significant difference in predation risk. Thus, size and being mobile (compared to sessility) are the primary risk factors influencing rotifer predation vulnerability. [ABSTRACT FROM AUTHOR]

The Brachionidae rotifer Kellicottia bostoniensis (Rousselet, 1908) is a transcontinental invader that continues to spread rapidly from the south to the north of the South American continent. We investigated the invasion of K. bostoniensis and its potential impact on the rotifer assemblage in a large tropical reservoir in southeast Brazil over a period of 9 years. The degree of K. bostoniensis invasion was confirmed by its frequency of occurrence (23%) and constant presence near to the main tributary, thus indicating propagule pressure from upstream. Differing environmental drivers regulated the invader in comparison with resident species. Nitrate and dissolved oxygen were important for native rotifers but not for K. bostoniensis, which negatively correlated with water temperature and positively with epilimnion depth. Total body length of K. bostoniensis increased from 2001 to 2009 as a result of an increase in size of most spines, which suggested a defensive strategy against predation. A functional approach applied to the rotifer assemblage indicated that the high species richness may be associated with high niche partitioning within the assemblage. The permanence of K. bostoniensis in the assemblage appears to be related to occupation of an empty niche. [ABSTRACT FROM AUTHOR]

The structure of many aquatic food webs is influenced by tadpole survivorship and duration of seasonal occupancy, which depend on tadpole diet. Pollen has been occasionally reported to occur in tadpole diets, and the available studies show that tadpoles have a strong preference for this supposedly nutritive resource. Thus, we aimed to test whether a diet composed of pollen from varied plant species would boost tadpole growth, development, and agility/mobility, compared to a regular artificial balanced and nutritive diet. Tadpoles in initial developmental stages 25 and 30 grew more when fed with pollen, compared to artificial food and a mixture of both diets. Those initially in stage 30 advanced more developmental stages during one month when fed exclusively with pollen. Tadpoles fed with pollen moved longer distances in response to an aversive stimulus simulating a predatory attack than tadpoles fed with artificial food or a mixed diet. Our results corroborate the hypotheses of pollen being a very important food source to aquatic consumers such as tadpoles, being likely to influence the structure of aquatic food webs through tadpole nutrition and modulation of growth/development speed, as well as tadpole ability to escape predators. [ABSTRACT FROM AUTHOR]

Bottom-feeding fish can exert strong top-down pressure on benthic invertebrates while also causing mechanical disturbance of the sediment. In our laboratory study, we investigated the influence of predation and disturbance-induced water column emigration on meiofauna, triggered by the armored catfish Corydoras aeneus. We hypothesized that both factors would significantly reduce the abundance of meiofauna, depending on their body size. Accordingly, we also expected a change in the nematode community structure. After 24 h, the abundances of nematodes, tardigrades, hydracarina, copepods and oligochaetes were significantly lower than in control aquariums without fish, in the latter two groups primarily due to predation. All other taxa were equally affected by predation and emigration. Within the nematodes, mainly large individuals (≥ 1 mm) were consumed, while smaller worms (< 1 mm) were increasingly dispersed. This, though it did not reduce species numbers, resulted in altered size and species composition. Our results show that the real top-down effects can quickly be overestimated as emigration of prey is overlooked and, on the other hand, that fish may also influence adjacent, undisturbed areas due to subsequent immigration of meiofauna. [ABSTRACT FROM AUTHOR]

Anthropogenic activities alter community composition, diversity and functioning of macroinvertebrate communities in freshwater ecosystems. Especially threatened are pond ecosystems, given their small size, low protection, and typically high connection to adjacent agricultural lands and urban areas. Most of the existing research, however, focuses on benthic macroinvertebrates while the evidence for epiphytic macroinvertebrates is strongly limited. Here we tested the effects of different anthropogenic activities on abundance, taxonomic and functional diversity, and composition of epiphytic macroinvertebrates in ponds along the gradients of local environmental factors. We found that all types of anthropogenic activities had negative impact on abundance, and on both taxonomic and functional diversity, and altered taxonomic and functional composition of epiphytic macroinvertebrates. Among the local environmental factors, macrophyte growth forms governed diversity and community composition, having positive effects on the taxonomic diversity, but allowing only a narrow spectrum of macroinvertebrate functional traits to persist on a single growth form of macrophytes. Fish predation was an important determinant of functional diversity of epiphytic macroinvertebrates. Our findings suggest that management strategies aimed to maintain high levels of biodiversity in ponds should be directed towards reducing the level of anthropogenic pressure, while ensuring the presence of distinct macrophyte growth forms in ponds. [ABSTRACT FROM AUTHOR]

The aim of our work was to experimentally test the hypothesis that changes in the thermal stratification in lakes of the temperate zone, expected as a result of progressive global warming, will cause an increase in fitness costs in a planktonic cladoceran Daphnia, associated with diel vertical migrations. In a programmable thermostatic chamber, Daphnia magna have been cultured from the first juvenile instar till the first reproduction, in thermal regimes corresponding to the conditions experienced by non-migratory (remaining in epilimnion day and night) and migrating (spending nights in epilimnion and days in hypolimnion) animals. We exposed Daphnia to thermal regimes: corresponding to the temperatures typically reigning stratified lakes nowadays (20 °C in epilimnion and 8 °C in hypolimnion), and expected at the end of this century (28 °C and 12 °C, respectively). The analysis of life-history parameters confirmed the assumption of an increase in metabolic costs resulting from vertical migration of Daphnia along with the expected increase in temperature differences between epilimnion and hypolimnion, which is a daily anti-predator refuge for migrating animals. This may consequently lead to significant changes in the composition of lake zooplankton communities, i.e., to an increase in the share of non-migrating species with small body sizes. [ABSTRACT FROM AUTHOR]

To test the hypothesis that non-consumptive predation pressures favor genotypes that have higher equilibrium densities or mictic ratios, we expose replicate populations of the rotifer Brachionus angularis to low (LK) and high (HK) concentrations of predator Asplanchna kairomones. Over 75 days (25 asexual generations) of selection, LK-treated populations have higher equilibrium densities and lower mictic ratios than the control populations. The opposite occurs for HK-treated populations. These results suggest that compared with the control, LK and HK select for genotypes with higher equilibrium densities and mictic ratios, respectively. Common garden bioassays reveal that in the absence of Asplanchna kairomones, populations with an LK selection history have a higher average intrinsic rate of population increase, and those with an HK selection history have a higher average mictic ratio than those with the control selection history, which suggest that adaptations to LK and HK increase average intrinsic rate of population increase and mictic ratio of prey populations, respectively. Increased intrinsic rate of population increase and mictic ratio can serve as strategies of offsetting mortality from predation and escaping the predator, and thus enable prey to survive low and high predation pressures, respectively. [ABSTRACT FROM AUTHOR]

Cannibalism (i.e., intraspecific predation) affects the population dynamics of many invertebrate species. Cannibalism by the predatory cladoceran Bythotrephes cederströmii Schödler, 1863 has been observed and noted in laboratory settings on several occasions, but no studies have published results of cannibalism experiments or explicitly quantified Bythotrephes cannibalism rates. We performed two laboratory experiments that demonstrated and quantified Bythotrephes cannibalism. Cannibalism occurred frequently in our experiments, and cannibalism clearance rates were comparable to those for Bythotrephes feeding on heterospecific prey. Further, our estimates of clearance rates between conspecifics suggest that cannibalism could be an important food source during certain periods of the year, and in particular places, for which Bythotrephes densities are at the higher end of observed ranges. While more research is needed, our results suggest that there are conditions in which cannibalism should be included in models of Bythotrephes predation, including bioenergetics models predicting Bythotrephes consumption rates. [ABSTRACT FROM AUTHOR]

They found a low parasite diversity and load on the three autochthonous cichlid species, I Coptodon guineensis i (Günther, 1862), I C. zillii i (Gervais, 1848), and I Oreochromis aureus i (Steindachner, 1864), with evidence for host-switching between different cichlid genera and potential synxenic diversification in one of the I Cichlidogyrus i species. In their review, Geletu and Zhao ([22]) discuss the increasing importance of Nile tilapia for food production globally, and they outline the value of the native genetic resources of tilapia species for future enhancement and resilience of tilapia-based aquaculture. Well-bred: how cichlids raise their young and stand their ground (or not) Cichlid fishes show elaborate mate choice and brood care behavior, and the effort invested in securing mates and rearing offspring also invites the expression of alternative tactics (Sefc, [51]). Guest editors: S. Koblmüller, R. C. Albertson, M. J. Genner, K. M. Sefc & T. Takahashi / Advances in Cichlid Research V: Behavior, Ecology and Evolutionary Biology The current special issue is the fifth in a series of special issues published in I Hydrobiologia i exclusively devoted to cichlid fish research. [Extracted from the article]

The strength of trophic and non-trophic interactions in predator–prey dynamics may be modified by predator density/diversity and prey size characteristics. In aquatic environments, multi-dimensional scaling of search areas (water depth and surface area) may mediate interactions among predators, with implications for prey risk. Here, we used a comparative functional response (FR) approach to investigate the effects of search area, predator composition and prey size on the strength of trophic and non-trophic interactions in freshwater habitats. A model system comprising two predatory notonectids (Anisops breddini and Anisops sardeus) was examined consuming four larval instar prey of Culex quinquefasciatus mosquitoes at nine different arena sizes, consisting of three crossed levels of surface area and water depth. Type II FRs were most common among predator groups, with 2nd instar prey consumed the most overall. Here, A. sardeus exhibited significantly higher feeding rates as compared to A. breddini, particularly in shallow waters. Non-trophic interactions in conspecific A. breddini and heterospecific pairs were mostly negative, indicating reduced prey risk. Further, predator–predator antagonisms were most pronounced in the heterospecific pairs. Strength of trophic and non-trophic interactions is thus dependent on complex interplays between the characteristics of predator–prey participants in combination with environmental heterogeneities. [ABSTRACT FROM AUTHOR]

Topshell gastropods are among the most important intertidal biofilm grazers. Present throughout the Mediterranean, this sea's only exclusively eulittoral trochid, Phorcus turbinatus, is spatially separated from its infralittoral congeners, P. articulatus, P. richardi and P. mutabilis. Despite its ubiquity, data on its fundamental ecology are lacking. By a series of laboratory and field experiments, I show that predation fixes the lower boundary of the vertical range inhabited by P. turbinatus precisely at lowest astronomical tide (LAT). Predicted in situ predation risk rapidly increases from 30% d–1 at the mean position of P. turbinatus (+0.31 m) to 84% d–1 at 1 m below LAT. At least nine predators across all major phyla prey on P. turbinatus. Important in terms of abundance, zonation and frequency of predation events are the two muricids Stramonita haemastoma (+0.08 m) and Hexaplex trunculus (−1.73 m) on exposed and sheltered coasts, respectively, along with Thalassoma pavo (−0.56 m) and Hermodice carunculata (−1.24 m). Physiological constraints seem to be of secondary importance since P. turbinatus survives up to 1 week fully immersed in situ. Therefore, predation risk likely is the ultimate driver of vertical distribution and thus physiological adaptation of littoral Mediterranean trochids. [ABSTRACT FROM AUTHOR]

Understanding the environmental effects of chemicals used in pest control on aquatic systems is crucial to ensure the conservation of beneficial non-target organisms. Mosquito larvicides are commonly applied to aquatic habitats; however, their non-target effects are not well understood. Our goal was to determine lethal and behavioral effects of insect growth regulators (IGRs) and surface films (SFs) on predaceous diving beetle adults and larvae, and damselfly and dragonfly nymphs in roadside ditch habitats. Behavioral effects were determined via bioassays quantifying predator movement, location, and larval mosquito predation. Using Principal Components Analyses, correlated behaviors were determined for each taxa, and compared within SF and IGR treatment levels. Surface films were lethal to beetle adults in the genus Laccophilus (Dytiscidae) at recommended and high concentrations. Laccophilus adult behavior changed in response to IGRs, those exposed to recommended and high concentrations were more active than controls. Larval Laccophilus mosquito consumption varied between SFs and IGRs. We conclude that SFs can harm aquatic organisms that require atmospheric oxygen, and both larvicides may have sublethal effects on hunting behaviors of aquatic insects. Future studies should focus on different larvicides, and a wider variety of aquatic taxa that interact with mosquito larvae. [ABSTRACT FROM AUTHOR]

Biological invasion is a strong threat to native biodiversity, with limnic systems being especially vulnerable due to historical separation and resulting prey naivety. The prey naivety hypothesis states that native species may not be able to recognize novel predators due to a lack of common evolutionary background and, therefore, become easy targets. In a laboratory experiment, we added cues of native European bullhead (Cottus gobio Linnaeus, 1758) and invasive round goby [Neogobius melanostomus (Pallas, 1814)] to Ancylus fluviatilis Müller, 1774 originating from two different populations within the same river (one naive, one experienced towards round goby) and compared their predator avoidance behavior. Individuals from both populations recognized cues from the known predator C. gobio and reduced their locomotive activity. To round goby cues, however, naive individuals did not respond, thereby supporting the prey naivety hypothesis. Experienced individuals, in contrast, reduced their activity, suggesting a learning effect due to the co-occurrence of invasive predator and prey. At fast moving invasion fronts of highly invasive species like N. melanostomus, prey naivety can, hence, enhance their negative impact on ecosystems. Behavioral adaptation of native species resulting in predator avoidance reactions could, therefore, play an important role in ecosystem resilience and temporal invasion dynamics. [ABSTRACT FROM AUTHOR]

To understand the spatiotemporal overlap in the habitat use of sympatric predators, we studied longitudinal activity and reservoir section and depth use of pike (Esox lucius), pikeperch (Sander lucioperca) and catfish (Silurus glanis) in the Římov Reservoir, using an autonomous telemetry system for 11 months. We found significant differences among these species in studied parameters that varied considerably over tracked period. Pike consistently used the same sections of the reservoir, while pikeperch and catfish frequently visited a tributary during the warm season (late spring and early autumn), and moved closer to the dam during the cold season (late autumn to early spring). Pike longitudinal activity was highest in the cold season, pikeperch in the warm season, and catfish activity peaked in both seasons. Overlap in the depth use among species was higher in the warm season, when all species used the upper layer of the water column, and lower in the cold season, when pikeperch and catfish used deeper areas. These results demonstrated overlay and temporal variation of habitat use among these predators, as well as potential spatiotemporal space for their direct ecological interactions. [ABSTRACT FROM AUTHOR]

Fisheries ecosystem-based management is an important tool for sustainable harvesting of fisheries worldwide. Knowledge of trophic interactions is crucial since changes in trophic balances can induce severe changes in the structure of marine communities. While advocated for deep-sea fisheries, a lack of studies in the benthopelagic area persist. The Antarctic toothfish, Dissostichus mawsoni, is a top predator inhabiting the Southern Ocean deep-sea and a high-value species in a fishery managed by CCAMLR (Commission for the Conservation of Antarctic Marine Living Resources). Previous studies suggested a geographical variability in its diet, but never studying it in the same year. We analysed stomach contents and stable isotopes of δ15N and δ13C in the muscle of D. mawsoni captured in three fishing areas from the Amundsen and Dumont D'Urville Seas, during the 2016/17 fishing season. Although significant spatial differences were found, five taxa were found in all sites, Antimora rostrata, Macrourus spp., Muraenolepis spp., Moroteuthopsis longimana and Psychroteuthis glacialis. High diversity of prey confirms D. mawsoni as a generalist feeder. Values of δ15N showed similar trophic position across areas, in contrast to the differences found in δ13C values. GLM showed that δ15N and δ13C values varied with otolith length, latitude and the opposite isotope, i.e. δ13C and δ15N respectively. Implications for D. mawsoni fisheries management are discussed considering different predation release scenarios. [ABSTRACT FROM AUTHOR]

Modern biological invasions represent a major facet of the Anthropocene, yet the invasive potential of species remains poorly understood. In this context, this study compared ecological traits of native and non-native populations of Cichla kelberi, a powerful invader, to investigate the hypothesis that this fish exhibits phenotypic and behavioral variations, which may confer adaptability to different conditions. Data on population structure, trophic ecology, and reproduction were collected from populations in different Neotropical impoundments. We found differences in population structure, with larger mean sizes and a lower proportion of juveniles in the native population. All populations exhibited piscivore behavior, but a higher incidence of empty stomachs and a less diverse diet characterized some non-native populations, with the consumption of non-fish resources and cannibalism. Non-native populations also showed prolonged reproduction and early maturity. In general, differences were not restricted to the contrast native vs. non-native, as introduced populations showed considerable divergence among themselves. Results confirmed the existence of phenotypic and behavioral variation in C. kelberi, which must affect its invasive potential by conferring adaptability to novel conditions in specific localities and contexts. These aspects make C. kelberi an almost certain invader of artificial impoundments located in tropical ecosystems of the world. [ABSTRACT FROM AUTHOR]

Invasive alien anurans are introduced worldwide in freshwater ecosystems where they can have a strong impact on native organisms such as amphibians. The risk for natives is dependent on the degree of niche overlap and co-occurrence in pond-breeding sites. In the present study, we focused on alien marsh frogs (Pelophylax ridibundus) that are invading nationwide areas in Western Europe and which prey on both caudates and anurans. We assessed aquatic habitat preferences, pond use and environmental niche overlap between invasive populations of marsh frogs and five species of native amphibian prey of the Larzac plateau (southern France). Due to their large environmental niche, marsh frogs have become the most ubiquitous amphibians in the area. Occupancy models revealed that they had aquatic habitat preferences (e.g., water depth and aquatic vegetation) similar to most species of native amphibians. This resulted in a large overlap between the environmental niche of the invader and its potential prey. The frequent coexistence in ponds therefore exposed native species to predation risk and other potential disturbances caused by marsh frogs. Altogether, these results highlight on the risks posed by such opportunist invaders for native amphibians that occur in their wide invasion range. [ABSTRACT FROM AUTHOR]

Marine ecosystems on continental shelves face multiple challenges due to anthropogenic disturbances, many of which can change the seawater stoichiometry (C:N:P) and consequently elemental ratios of phytoplankton. This change in food quality may not be tolerated by all grazers and predators. Gelatinous and soft-bodied zooplankton (GZ) might be more resilient to such changes. We sampled GZ species in neritic and oceanic waters of the Northeast Pacific off British Columbia, Canada, determined their phosphorus (P) content and elemental ratios (C/P, N/P), and analysed intraspecific variability associated with size and ontogeny. P content was measured for twelve GZ taxa. P % DW (dry weight) decreased with size for the hydrozoan Aequorea sp., scyphozoans Aurelia labiata, Cyanea capillata, and the thaliacean Salpa aspera, and differed significantly for two development stages of the salp S. aspera. While C/P and N/P were mostly size and stage independent, they were highly variable. C/P values of GZ were generally higher than values of crustacean zooplankton, indicating that GZ represent poor-quality prey for non-GZ predators, and that GZ may have a higher resilience towards P-limited (low quality) prey. Changing ocean conditions and nutrient stoichiometry of prey may favour GZ, although large variability in P dynamics among GZ taxa and uncertainty about future ocean stoichiometry changes make generalisations difficult. [ABSTRACT FROM AUTHOR]

An important group of protozooplankton, the ciliates, are a crucial component of aquatic food webs. They are the main grazers on bacteria and algae transferring carbon to higher levels of the food web (metazooplankton and fish fry). Changes in the quality and quantity of protozooplankton can modify the quality and quantity of metazooplankton, especially predatory copepods, causing changes in energy transfer and the matter cycle. Observable climate change is one of the most significant factors promoting the increase of cyanobacterial blooms. Therefore, the aim of this study was to find out how cyanobacterial blooms modify relationships between ciliates (prey) and copepods (predator), and to discover possible pathways of changes in freshwater food webs. We analysed the relationship between the biomass of predatory copepods and feeding guilds of ciliates (algivorous, bacterivorous, bacteri-algivorous). The relationship of predators biomass with algivorous and bacteri-algivorous ciliate biomasses, with a simultaneous lack of relationship with bacterivorous ciliate biomass, demonstrates that bacterial fixed carbon may be only partially contributing to the total energy passed through this link. Results demonstrated that the bloom enhanced the relationship between prey and predator. Larger and free-swimming ciliate species appear to play a greater role in energy transfer than smaller sedentary species. [ABSTRACT FROM AUTHOR]

Reductions in aquatic habitat size facilitate encounters between predators and prey by reducing the height of the water column and the water volume. Here, we proposed to disentangle the effects of these mechanisms on predation rates and parameters of functional response curves of predators. We paired active-search predators (Buenoa, Hemiptera) or ambush predators (Pantala and Lestes, Odonata) with prey of different mobility types (Argyrodiaptomus, Copepoda; Culex, Diptera). Three treatments were established: high water column height and high water volume (H + V +), low water column height and high water volume (H − V +), and low water column height and low water volume (H − V−). We used contrast analysis to separate the effects of water column height (H + , H−) and water volume (V + , V−). Predation rates were higher in V− than in V + for Pantala and Buenoa consuming Argyrodiaptomus. In addition, we observed an increase in attack rates and a decrease in handling time in V− in relation to V + for Pantala and Lestes consuming Argyrodiaptomus. We concluded that reduction in the water volume was main responsible factor for the changes in predator–prey interactions. These changes depended on the prey behavior and predator foraging modes: ambush predators were the most benefited, and highly mobile prey were the most consumed. [ABSTRACT FROM AUTHOR]

Non-native species introductions are becoming increasingly common, but long-term consequences of the introduction of non-native predators on native prey species remains poorly understood. Bythotrephes cederströmii is an invasive zooplanktivore with potential negative impacts on Daphnia across North America. However, Daphnia may be responding to this invader by developing anti-predator defenses. We investigated whether escape ability of three Daphnia species (D. ambigua, D. mendotae, and D. pulicaria) differed in the absence and presence of Bythotrephes chemical cues, whether the escape ability of pre- and post- invasion clones of each Daphnia species differed, and whether the three Daphnia species differed in their escape ability. We conducted a series of transfer experiments in the presence and absence of Bythotrephes chemical cues to evaluate the escape ability of the three Daphnia species from both pre- and post-Bythotrephes invasion time periods. Comparison of Daphnia from pre- and post-invasion time periods revealed a constitutive increase in the escape ability of D. pulicaria which may help them avoid attack by Bythotrephes. These data contribute to a growing body of research that demonstrates that ecological invasions can prompt adaptive responses, altering the nature of interactions between invasive predators and native prey species. [ABSTRACT FROM AUTHOR]

By hindering migration and inducing direct turbine mortality during downstream migration, hydropower is regarded as one of the most serious threats to anadromous salmonids. Yet, little attention has been paid to long-term turbine-induced selection mechanisms effecting fish populations. This work evaluates turbine and post-turbine survival of PIT-tagged wild brown trout smolts. By estimating individual river and sea survival rates, we were able to compare survival rates of smolts that had migrated through the turbine with smolts that had bypassed the turbine, as well as investigate both natural and anthropogenic size-selective mechanisms operative on the population. Total river-descent survival probability was 0.20 for turbine migrants and 0.44 for bypass migrants. The surviving turbine migrants were significantly smaller than their bypass counterparts and more exposed to predation from Northern pike. The estimated mean-adjusted selection gradient was − 0.76 for turbine migrants and + 1.85 for the bypass migrants. The resulting disruptive selection may ultimately lead to increased phenotypic smolt size variation provided sufficient additive genetic variance associated with smolt size. Mitigation measures at hydropower plants are thus essential for preserving sustainable populations of anadromous fish and maintaining population genetic variation. [ABSTRACT FROM AUTHOR]

Metacommunity ecology provides a basis for understanding how ecological communities are assembled. Metacommunity theory can be applied to assess the effects of anthropogenic disturbance on freshwater communities. However, few studies have examined how species-specific responses to environmental covariates can generate broader patterns in freshwater metacommunities. I determined occupancy patterns in an amphibian metacommunity to identify important predictors of reproduction at wetland sites. I conducted surveys at 49 wetlands for tadpoles with fish traps and dip netting in an urbanising region in southeastern Australia. The larvae of seven frog species were detected. There were negative relationships between the probabilities of reproduction at a site and the relative abundance of the eastern mosquitofish (Gambusia holbrooki) and wetland electrical conductivity. There was a positive relationship between tadpole occupancy and the proportion of accessible habitat within 1000 m of a site, a measure of the combined effects of roads and habitat amount. These results highlight the negative effect of predatory Gambusia on frog communities and illustrate the importance of the species-sorting and mass-effect perspectives of metacommunity theory at multiple spatial scales. Habitat restoration projects for amphibians should remove exotic fish or prevent their establishment in managed wetlands and maintain habitat connectivity to facilitate dispersal. [ABSTRACT FROM AUTHOR]

At early life stages invasive fishes may have no innate or learned behavioral responses to native predators. However, social cues expressed by shoal mates is one strategy species use to assess risk. By shoaling and using social cues, fishes may identify and mimic others with anti-predator behaviors to increase their own survival. Ability of non-native fishes, such as bighead carp (Hypophthalmichthys nobilis), to mimic native species that have experienced predatory threats is not known. In this experimental study, we varied the number of experienced individuals and the species composition to contrast the responses of naïve juvenile bighead carp exposed to predatory kairomones when grouped with differing numbers of either experienced conspecific or experienced heterospecific (golden shiner, Notemigonus crysoleucas) shoal mates. We found fully naïve groups of bighead carp did not respond to largemouth bass kairomones, but that naïve individuals could mimic anti-predatory behaviors of experienced individuals, even when those experienced individuals were heterospecifics. Diverse alarm responses of bighead carp to composition and experience suggest that responses of this species are plastic. Through changing responses based on shoal experience level and composition, plastic social learning highlights how naïve individuals may adapt to novel predator threats, which could inform predictions of non-native persistence in novel waterways. [ABSTRACT FROM AUTHOR]

Fire retardants are commonly used for fighting wildfires. Retardant chemicals washed via runoff into aquatic systems may be concentrated, thus exposing aquatic species to high levels of ammonium, phosphate, and iron. These chemicals directly affect individual species, which can also cascade to the rest of the aquatic community. We investigated the effects of a prevalent fire retardant, FR CROS 134 (FR), at various concentrations (0 to 11.4 × 102 mg l−1) on larval fire salamander (Salamandra infraimmaculata) and aquatic community structure (bacteria, algae and invertebrates) using mesocosms. We show a negative effect of the presence of FR on the survivorship and time to metamorphosis of salamander larvae (94–17% and 48–64 days, respectively). Moreover, increasing FR concentrations were found to inhibit the predation rate of salamander larvae on mosquito larvae (89–14%). FR decreased the invertebrate community diversity with changes in composition and shifts in evenness and dominance (e.g., cladoceran species abundance increased, whereas calanoid copepod species declined). Finally, cyanobacteria and eukaryotic algal abundance increased, while heterotrophic bacterial abundance decreased with FR addition. The effects of fire retardants on biodiversity found here and the growing use of fire retardants worldwide call for additional evidence-based assessment of their impact, especially in aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Functional responses describe how the proportion of prey consumed by a predator changes as prey density changes. For predators consuming a single prey species, functional responses are determined by two parameters: attack rate and handling time. These parameters may be influenced by morphological and behavioral differences in prey stemming from interspecific or environmentally-driven processes. Here we investigate how interspecific morphological differences and changes in movement rate impact a predator's functional response. Using a flatworm predator (Stenostomum virginianum) consuming either Paramecium aurelia or P. multimicronucleatum we show that movement rate changes significantly with temperature, leading to changes in attack rate. We also show how body size affects the amount of time predators require to handle prey. We fit a mechanistic functional response model to demonstrate how changes in attack rate and handling time affect overall rates of predation. Our results demonstrate that S. virginianum attack rates are greater for P. aurelia than P. multimicronucleatum. In addition, higher temperature increases S. virginianum attack rates on both species, and reduces the time needed to handle P. aurelia. These differences in predation rate appear related to prey species' traits, and the temperature-mediated changes in these traits, highlighting the complex processes that underpin predator–prey interactions. [ABSTRACT FROM AUTHOR]

Outcomes of predator–prey interactions depend on biotic and abiotic factors. Habitat complexity, for example, mediates predator functional response type and parameters (attack rate and handling time). However, the relationship between habitat complexity and functional response varies across ecosystems. We assessed interactions between the giant water bug, Belostoma sp., and its prey, rams-horn snails, Helisoma trivolvis, across four prey densities (N = 2, 4, 8, 16 snails) and three habitat complexity levels (No-complexity, Low-complexity, High-complexity) to understand how complexity affected the functional response. We also tested effects of predator and prey body size on number of prey killed. Belostoma exhibited a Type III functional response in all habitat complexity treatments. Attack rate tended to increase with increasing complexity. Handling time was different among treatments, being lowest in the No-complexity treatment and highest in the Low-complexity treatment. Belostoma body size was positively related, while Helisoma body size was inversely related, to the number of Helisoma killed. We show habitat complexity does not affect the shape of predator functional response but impacts response parameters in the Belostoma–Helisoma system. We reaffirm that attack rate, handling time, and mortality outcomes for prey within predator–prey interactions are affected by abiotic factors through habitat complexity. [ABSTRACT FROM AUTHOR]

Corallivory causes considerable damage to coral reefs and can exacerbate other disturbances. Among coral predators, Drupella spp. are considered as delayer of coral recovery in the Republic of Maldives, although little information is available on their ecology. Thus, we aimed to assess their population structure, feeding behaviour and spatial distribution around 2 years after a coral bleaching event in 2016. Biological and environmental data were collected using belt and line intercept transects in six shallow reefs in Maldives. The snails occurred in aggregations with a maximum of 62 individuals and exhibited a preference for branching corals. Yet, the gastropods showed a high plasticity in adapting feeding preferences to prey availability. Drupella spp. were homogenously distributed in the study area with an average of 9.04 ± 19.72 ind/200 m2. However, their occurrence was significantly different at the reef scale with the highest densities found in locations with higher coral cover. The impact of Drupella spp. appeared to be minimal with the population suffering from the loss of coral cover. We suggest that monitoring programs collect temporal- and spatial-scale data on non-outbreaking populations or non-aggregating populations to understand the dynamics of predation related to the co-occurrence of anthropogenic and natural impacts. [ABSTRACT FROM AUTHOR]

In the presence of the predatory rotifer Asplanchna, some Brachionus and Keratella species develop inducible morphological, behavioral, and life history defenses that enable prey to survive predation pressure. However, whether clones belonging to the same rotifer species but with different behaviors (attached and free-swimming) exhibit divergent responses in morphology and life history remains largely unknown. In this study, neonates of an attached and a free-swimming clone of B. dorcas were exposed to media conditioned by A. brightwellii neonates at densities of 0 (control), 40, 80, and 160 ind l−1 for 24 h, and their morphological and life-table demographic parameters were measured and calculated. We showed that the Asplanchna kairomone significantly increased the propensity to attach in the attached clone only, with attached individuals effectively protected from Asplanchna predation. In response to increasing Asplanchna kairomone concentration, the attached clone did not show any morphological changes, but it did exhibit a decreased net reproductive rate and intrinsic rate of population increase. The free-swimming clone developed elongated posterolateral spines and a decreased intrinsic rate of population increase, as well as a decrease in the proportion of sexual offspring. Thus, both clones exhibited reproductive costs. [ABSTRACT FROM AUTHOR]

Introduced predators can negatively affect native prey species via either direct predation or through indirect effects such as behavioral changes or habitat shifts that lead to declines in growth, condition, and reproductive success. In freshwater habitats, salmonid fishes are one of the most common introduced predators worldwide. Most studies of effects of salmonids on native prey species have focused on direct predation, with fewer studies examining how behavior of prey is affected. We used a snorkeling protocol to examine whether introduction of rainbow (Oncorhyuchus mykiss) and brown (Salmo trutta) trout in streams was associated with increased wariness in two small prey fishes, darters in the genus Etheostoma. Wariness was measured as flight initiation distance (FID), the distance at which individuals flee from an approaching threat (snorkeler), for darters in four rivers with and four rivers without introduced trout. Darters in rivers with trout had longer FIDs, indicating that they were less tolerant of risk than darters in control rivers. Increased wariness could lead to darters decreasing activities associated with foraging and reproduction, which could have long-term negative effects on populations of these prey fishes. [ABSTRACT FROM AUTHOR]

Habitat structure and predation are major factors that influence the distribution of zooplankton species and functional traits. Here, we analyzed how the structure provided by macrophytes (richness, Shannon's diversity, and biomass) and potential predation by small-bodied fishes (richness and abundance) determine the richness of species and functional traits of zooplankton, as well as the spatial dissimilarity (beta-diversity) of species and traits. Zooplankton, fish, and macrophytes were simultaneously sampled across a gradient of 30 multi-species macrophyte beds. We assessed spatial patterns of zooplankton under taxonomic and functional approaches, using linear regression models, Generalized Dissimilarity Models, a Structural Equation Model, and a Fourth-Corner Analysis. Zooplankton taxonomic beta-diversity was most represented by the turnover component and zooplankton functional beta-diversity by nestedness. Zooplankton taxonomic richness and taxonomic beta-diversity were positively related to macrophyte biomass, richness, and Shannon's diversity, whereas zooplankton functional richness and functional beta-diversity were positively related to fish richness and abundance. Macrophyte biomass and diversity oppositely influenced fish structure, which had influence on zooplankton structure. Macrophytes also negatively influenced the zooplankton traits such as body size, reproduction type, habitat, lifespan, and predatory escape response and positively influenced the trait feeding type. Fish were negatively related to the trait body size. The spatial structure generated by macrophyte beds and fish community determined the distribution of zooplankton species and functional traits. [ABSTRACT FROM AUTHOR]

The population of horseshoe crabs, Tachypleus gigas, in Malaysian waters is declining due to overexploitation, pollution, and loss of natural habitats. As an initiative to increase their population, adult T. gigas were reintroduced in Setiu lagoon, Terengganu. In the interest of sustainable management of bivalve resources in that area, feeding experiments were carried out to determine quantity consumption and feeding preferences of adult T. gigas in captivity on four species of economically important bivalves from Setiu namely Scapharca cornea, Meretrix meretrix, Geloina expansa and Magallana bilineata. Tachypleus gigas consumed less than a single intact bivalve per day and the amount increased to almost twice when fed with bivalve flesh. Females T. gigas showed a preference for intact M. meretrix, whereas males showed preference for M. bilineata and M. meretrix when fed with flesh only. Our findings suggest that T. gigas may not prey upon live adult bivalves in Setiu as they only scavenge on dead or weak bivalves. However, the impact of horseshoe crab reintroduction on other small invertebrates in Setiu including the juveniles of these bivalves needs to be explored in order to ensure the success of this conservation effort. [ABSTRACT FROM AUTHOR]

Hydrilla verticillata is an aquatic weed that grows densely throughout the water column and is costly to manage. The hydrilla tip mining midge, Cricotopus lebetis, a potential augmentative biological control agent of hydrilla, feeds on the apical meristem preventing growth. The goal of this study was to quantify the influence of a predator (mosquitofish, Gambusia sp.) and a competitor (hydrilla leafcutter moth, Parapoynx diminutalis) and their interactions, on the ability of the midge to survive and feed on hydrilla. The first experiment involved six treatments established in 37.8 L tanks with combinations of the organisms, including larval C. lebetis. Survival to adult midge eclosion was significantly reduced in the presence of the predator but was unaffected by the competitor's presence alone. Apical meristem damage was reduced when both the competitor and predator were present. The second experiment included four treatments with C. lebetis egg masses or larvae and the presence or absence of mosquitofish. Adding C. lebetis as eggs rather than as larvae increased midge survival in the absence of the predator. Midge survival was lower when larvae were added, but the predator had no additional effect. To facilitate successful establishment of the midge and control of hydrilla, high numbers of larvae should be released to overcome predation. [ABSTRACT FROM AUTHOR]

Zooplankton play a key role in energy transfer within lake food webs, but we have a poor knowledge concerning their role as phytoplankton grazers in shallow subtropical lakes. In this study, we aimed to determine how zooplankton grazing upon phytoplankton is altered in different scenarios of fish predation and turbidity, and we explored the relevance of grazing compared to other environmental variables, to explain phytoplankton biomass changes. A mesocosm experiment was conducted by including the following treatments: fish, turbidity, fish + turbidity, and a control (without fish or varying turbidity). The experiment lasted 21 days, and samples were taken four times. Zooplankton grazing was only effective for the microphagous group upon Cryptophyceae, while large Chlorophyceae and small pennate Bacillariophyceae biomass were benefited in the presence of copepods and cladocerans, being negatively affected by depletions in nitrogen availability. In the turbidity treatment, a reduction in phytoplankton biomass was obtained, artificially increasing zooplankton grazing on phytoplankton, while fish presence inhibited grazing of adult copepods and cladocerans. The other groups of phytoplankton were only influenced by the environment. This experiment suggests that phytoplankton biomass variations would be more affected by the environment than by zooplankton grazing in shallow lakes from the Paraná River. [ABSTRACT FROM AUTHOR]

Shallow lakes can change states in response to manipulations of top predators. In most reported experiments, the top piscivore has been a fish. However, low-latitude lakes typically support non-piscine piscivores, including mammals, birds, and reptiles. The roles of these groups have been little investigated, and whether they are more important as piscivores than fish remains unknown. We report both a longitudinal (2001–2018) and a cross-sectional (2012) study of the bird, caiman, and giant otter populations of floodplain lakes in Perú's Manu National Park. We compare the three groups, after removing the effects of taxonomic status and body mass, using allometric equations to estimate the field metabolic rate (FMR) for each group in each lake. Giant otters emerge as the dominant piscivore in lakes that support a resident family, with an energy requirement more than twice that of piscivorous birds and more than seven times that of caiman. However, giant otters were resident in only eight of 27 surveyed lakes. Indirect evidence suggests that these eight lakes are more productive than lakes not occupied by otters. The fact that lakes occupied by otters are dominated by phytoplankton suggests an underlying five-tiered trophic structure in keeping with the prominence of alternating levels in the structure of food webs. [ABSTRACT FROM AUTHOR]

Cannibalism can be a significant factor limiting the survival of pike, Esox lucius, early life stages in both natural and aquaculture conditions. In the present research, type I cannibalism was studied in pike larvae (size range: 9–32.5 mm standard length, SL) in controlled conditions for 45 days post-hatching (dph). For this purpose, the occurrence of cannibalistic pairs, i.e. prey caught by a cannibal inside the cannibal's mouth, was monitored for 15 min periods by two observers six times daily. Cannibalism was not observed in fish that still had yolk-sacs, but it did occur as soon as the yolk-sac was absorbed on 5 dph at a body size of 13 mm at 22 °C and 10 dph at a body size of 13.4 mm at 15 °C. The ratio of prey to predator size was on average 87%, but the smallest observed size difference was only 1.3%. The intensity of cannibalistic attacks depended on water temperature with more intense cannibalism at 22 °C than at 15 °C, and no cannibalism at 10 °C. Fluctuating asymmetry (FA) in all three sagittal otolith size parameters (area, width, and length) was higher in prey than in cannibals, the differences were not statistically significant. [ABSTRACT FROM AUTHOR]

The strength of interspecific competition and predator–prey interactions depends on the area of co-occurrence of the interacting species. Therefore, it is necessary to quantify the changes in the spatial overlap of trophically connected species to understand the outcomes of species interactions. In the Baltic Sea, the interplay between cod and flounder has previously been neglected. In this study, we use four decades of data on cod and flounder distributions covering the southern and central Baltic Sea to: (1) model and map the changes in the distributions of the two species using generalized additive models; (2) quantify the temporal changes in the potential competitive and predator–prey interactions between them using spatial overlap indices; (3) relate these changes in overlap to the known dynamics of the different cod and flounder populations in the Baltic Sea. Competition overlap has continuously increased for cod, from the beginning of the time-series. This is a possible cause of the observed decline in feeding levels and body condition of small and intermediate sized cod. Flounder overlap with large cod instead has decreased substantially, suggesting a predation release of flounder, potentially triggering its increase in abundance and distribution range observed in the last decades. [ABSTRACT FROM AUTHOR]

Fish respond to predation threat by size/cohort-dependent presence in particular habitats and this may contribute to sexual segregation between habitats in species with sexual size dimorphism (SSD). The present study examines the validity of the "predation risk hypothesis" and importance of SSD on habitat (pelagic/inshore) segregation and dietary differences between sexes in three cyprinids with various magnitudes of SSD-roach (Rutilus rutilus), freshwater bream (Abramis brama) and bleak (Alburnus alburnus). Fish were sampled using gillnets over five consecutive years in the Římov Reservoir. Habitat segregation with female overrepresentation in the pelagic habitat was found in the most sexually dimorphic species with 26% bigger females—the roach. When analysis of habitat segregation was size-controlled, this segregation ceased to confirm the importance of SSD. Freshwater bream sexes (2% SSD) differed in diet but did not differ in habitat occupation. Bleak sexes were not segregated. Larger roach individuals (predominantly females) are less threatened by gape-limited predators and consequently they can occupy the risky but optimal (for zooplankton acquisition) pelagic habitat. Our results demonstrate that habitat segregation is present in the species with the most pronounced SSD. [ABSTRACT FROM AUTHOR]

In tropical climates, free-floating aquatic plants may dominate shallow lakes and affect trophic interactions between zooplankton and their predators have been presented as an important subject to be investigated. The present study used mesocosms within a tropical lake in rural São Paulo-Brazil to test the hypothesis that free-floating macrophytes (FFM) reduce predation pressure on prey, as these aquatic plants provide refuge and shade. Fish predation by Astyanax lacustris was observed with the presence and absence of the FFM Eicchornia crassipes over a period of 5 weeks. FFM promoted a more diverse community structure by providing new habitats, especially for small- to medium-sized littoral cladocerans. Tropocyclops prasinus meridionalis were more abundant with the presence of macrophytes. Furthermore, the size distribution of zooplankton differed between treatments at the end of the experiment, in which the larger organisms were less abundant in the treatment with FFM. The present study suggests that FFM affected the interactions between zooplankton and predators, but this influence occurred due to the macrophytes acting as refuge to smaller organisms rather than large-sized individuals. The results also indicated that the macrophytes influenced the zooplankton community by contributing to an increased species richness. [ABSTRACT FROM AUTHOR]

There is growing evidence that species' traits may diverge during biological invasions; however, we still lack a general understanding of how the invasion process affects behavior. We used a biogeographic approach to compare foraging and antipredator behavior across a reciprocal invasion (in which each species invaded the native range of the other) of virile (Faxonius virilis) and rusty crayfish (F. rusticus). We hypothesized that the invasion process would select for individuals that invest more in foraging and less in defense than their native counterparts. We used laboratory experiments to examine crayfish boldness, activity, and foraging voracity and mesocosm experiments to examine antipredator behavior in response to fish. Non-native virile crayfish (Indiana, USA) were less bold, active and voracious than native virile crayfish (Wisconsin, USA), and they exhibited more antipredator behavior. Non-native rusty crayfish (Wisconsin) were more active in mesocosms and exhibited less antipredator behavior than native rusty crayfish (Indiana). Combined, these findings suggest a growth/mortality trade-off. Counter to our hypothesis, relative investment in foraging versus predator avoidance differed across regions and was not consistently associated with native or invasive populations. Thus, the substantial divergence in behavior we observed may by driven by local adaptation. [ABSTRACT FROM AUTHOR]

Habitat structure can profoundly influence interaction strengths between predators and prey. Spatio-temporal habitat structure in temporary wetland ecosystems is particularly variable because of fluctuations in water levels and vegetation colonisation dynamics. Demographic characteristics within animal populations may also alter the influence of habitat structure on biotic interactions, but have remained untested. Here, we investigate the influence of vegetation habitat structure on the consumption of larval mosquito prey by the calanoid copepod Lovenula raynerae, a temporary pond specialist. Increased habitat complexity reduced predation, and gravid female copepods were generally more voracious than male copepods in simplified habitats. However, sexes were more similar as habitat complexity increased. Type II functional responses were exhibited by the copepods irrespective of habitat complexity and sex, owing to consistent high prey acquisition at low prey densities. Attack rates by copepods were relatively unaffected by the complexity gradient, whilst handling times lengthened under more complex environments in gravid female copepods. We demonstrate emergent effects of habitat complexity across species demographics, with predation by males more robust to differences in habitat complexity than females. For ecosystems such as temporary ponds where sex-skewed predator ratios develop, our laboratory findings suggest habitat complexity and sex demographics mediate prey risk. [ABSTRACT FROM AUTHOR]

Animal behaviors are often well adapted to their environments. Predation risk avoidance is one of them. However, the fitness effects of behavioral variation associated with predation risks are poorly understood for aquatic organisms. In this study, we evaluated the effects of traits (origin and body size) and behaviors (regular defensive and post-stimulus behaviors) of masu salmon [Oncorhynchus masou masou (Brevoort, 1856)] on their predation risk. We first conducted aquarium experiments examining the behaviors of fish, followed by an evaluation of their survival after release in a semi-natural stream. After 56 days of the stream test, 48.3% of the released fish were lost. On-site camera trapping identified an ambush predator, the grey heron (Ardea cinerea Linnaeus, 1758), as the most frequently visiting predator. By individually matching the fish behaviors in the aquarium test with their survival in the stream, we found that the most critical determinant for the survival of fish in a semi-natural stream was their regular defensive behavior (i.e., hiding behavior when they were NOT exposed to a mimicked bird attack), rather than their post-stimulus behavior. Our results indicate that regular defensive behavior can be most beneficial to prey survival, at least when they are faced with ambush predators. [ABSTRACT FROM AUTHOR]

Understanding the relative importance of habitat and biotic drivers on community assembly across food web components is an important step towards predicting the consequences of environmental changes. Because documenting entire food webs is often impractical, this question has been only partially investigated. Here, we partitioned variation in species assemblages of the major components of tank bromeliad food webs (bacteria, algae, protozoans, detritivorous and predatory invertebrates) into habitat and biotic determinants and examined the influence of habitat variables and predator or prey abundance on all taxonomic assemblages. Ecological determinism of assemblage structure ranged from weak in bacteria (< 10% of the explained variance) to strong in predatory invertebrates (90%). Habitat features and canopy openness significantly influenced species assemblages; however, prey or predator density had far and away the most significant structuring effects. If biotic forces are at least as important as the abiotic forces while the importance of stochasticity declines towards upper trophic levels, then trophic levels could respond differently to natural or anthropogenic disturbance and to shifts in species distributions. The effects of such differential responses on food web reconfiguration, however, remain to be elucidated. [ABSTRACT FROM AUTHOR]