Predation Regimes Research Articles

Size and fecundity variation in populations of Poecilia vivipara Block & Schneider (Teleostei; Poeciliidae) inhabiting an environmental gradient

The reproductive variables [female size (geometric centroid size), fecundity and offspring size (longest diameter of the embryo)] of the livebearer Poecilia vivipara in the quaternary lagoons of northern Rio de Janeiro State varied significantly among sites and were partially associated within and among sites. Mean female size was directly related to salinity. Fecundity (number of offspring) was directly related to female size both within and among sites. The female size × fecundity relationship, however, was not constant among sites. Offspring size was partially and directly associated with female size and salinity. The relationship between fecundity and female size was positively related with fecundity, suggesting a non‐linear relationship of these variables when the total sample was considered. The results suggest that life‐history differences among sites were more related to different predation regimes than to simple effects of plasticity caused by increased growth in saltwater environments.

Mate choice, sexual coercion and gene flow in guppy populations

The role of behaviour in gene flow in Trinidadian guppies Poecilia reticulata was assessed using fish from an upstream and downstream pair of populations that differ in predation regime. High‐predation (downstream) females preferred males from the corresponding low‐predation population, but high‐predation males achieved greater reproductive success under competition. This suggests that post‐copulatory as well as pre‐copulatory events are important in determining rates of gene flow.

Postautotomy tail activity in the Balearic lizard, Podarcis lilfordi

Caudal autotomy is an effective antipredator strategy widespread among lizards. The shed tail thrashes vigorously for long periods to distract the predator and facilitate the lizard's escape. This movement is maintained by energy supplied by the anaerobic conversion of glycogen into lactate. It has been suggested that lactate accumulation serves as an index for the vigor of tail thrashing. We made three predictions: (1) tail loss frequency should be higher under heavier predation regime, (2) the duration of postautotomy tail movement should be extended in populations under heavy predation pressure as an adaptation to the higher risk and the increased need for defense, and (3) as result, lactate in these tail tissues should be concentrated at higher levels. To eliminate the impact of phylogeny and environmental factors on the interpretation of our result, we focused exclusively on one species, the Balearic lizard (Podarcis lilfordi). We studied three populations under different predation pressure but sharing the same climatic conditions. We found no differences among the studied populations either in postautotomy duration of tail movement or in levels of final lactate accumulation while autotomy frequency was higher where predation pressure was more intense. Tail loss effectiveness is directly influenced by the level of predation, while secondary features of the trait appear to remain independent from the impact of environment.

Competition and niche partitioning in a floodplain ecosystem: a cladoceran community squeezed between fish and invertebrate predation

Seasonal floodplains occasionally comprise highly productive zooplankton communities which are exposed to rapid shifts in predator regimes, also between vertebrate and invertebrate predators.We recorded the impact of two co-occurring zooplankton predators, the notonectid Anisops sardea and 0+ fish fry of Tilapia rendalli (max gape size 1 mm), on a cladoceran community dominated by Ceriodaphnia reticulata (0.25–0.78 mm), Daphnia laevis (0.6– 1.8 mm) and Scapholeberis kingi (0.27–0.8 mm). Both predators strongly reduced abundance of all prey species, yet with a striking size-selective effect for Daphnia prey only, where fish showed a strong preference for small individuals, while Anisops preferred large Daphnia individuals. This contrasts with the general view of size selection in invertebrate versus vertebrate predators, but is logically caused by the feeding mode of the notonectid, and the gape size limitation of the fish fry. The two predators also showed a dietary niche differentiation in terms of both prey selection and habitat choice. T. rendalli fed preferably on small species and size classes, whereas predation from A. sardea concentrated on large prey. Competitive interference was indicated when feeding on Ceriodaphnia, and niche partitioning when feeding on the two other species. The predatory pattern suggests long-lasting coexistence in the system.

Competition and niche partitioning in a floodplain ecosystem: a cladoceran community squeezed between fish and invertebrate predation

Seasonal floodplains occasionally comprise highly productive zooplankton communities which are exposed to rapid shifts in predator regimes, also between vertebrate and invertebrate predators.We recorded the impact of two co-occurring zooplankton predators, the notonectid Anisops sardea and 0+ fish fry of Tilapia rendalli (max gape size 1 mm), on a cladoceran community dominated by Ceriodaphnia reticulata (0.25–0.78 mm), Daphnia laevis (0.6– 1.8 mm) and Scapholeberis kingi (0.27–0.8 mm). Both predators strongly reduced abundance of all prey species, yet with a striking size-selective effect for Daphnia prey only, where fish showed a strong preference for small individuals, while Anisops preferred large Daphnia individuals. This contrasts with the general view of size selection in invertebrate versus vertebrate predators, but is logically caused by the feeding mode of the notonectid, and the gape size limitation of the fish fry. The two predators also showed a dietary niche differentiation in terms of both prey selection and habitat choice. T. rendalli fed preferably on small species and size classes, whereas predation from A. sardea concentrated on large prey. Competitive interference was indicated when feeding on Ceriodaphnia, and niche partitioning when feeding on the two other species. The predatory pattern suggests long-lasting coexistence in the system.

Effects of colonizing predators on yellow perch (Perca flavescens) populations in lakes recovering from acidification and metal stress

We examined the effects of predator species on yellow perch (Perca flavescens) from lakes in the Sudbury mining region (Ontario, Canada), where fish communities are just beginning to recover from the effects of decades of acidification and metal stress. The predation regimes investigated included six lakes with no predators, four lakes recently invaded (≤3 years) by predators, and eight lakes with well-established (≥15 years) predator populations. Netting survey results indicated that yellow perch biomass was 69% lower in lakes with predators. In lakes recently invaded by predators, perch displayed earlier ontogenetic diet shifts from zooplankton to benthos and much poorer growth during their first growing season. Energy investment (lipid content per egg) in eggs by mature females was also less in the lakes recently invaded by predators. Growth potential in adult perch (age 1), estimated by nucleoside diphosphokinase, was highest in lakes with established predators. Body condition, controlling for size of perch, was also greatest in established predator lakes. Perch body shape in lakes with predators showed a shift from a typical streamlined, pelagic body form towards a deeper-bodied benthic body form, a change that may increase foraging efficiency for benthos or represent an antipredator strategy.

Morphology and density of mussels on natural and aquaculture structure habitats: implications for sea duck predators

We compared density and morphology of wild mussels Mytilus trossulus growing natu- rally on shellfish farming structures to that of mussels from nearby intertidal areas, and considered the relevance to molluscivorous sea ducks. Mussel density on aquaculture structures greatly exceeded that of intertidal areas and farm mussels were larger, had lower shell mass, and had weaker byssal attachments. Differences in environmental conditions and predation regimes through- out the summer growing season were likely responsible for these differences. These morphological and density differences, in turn, have important implications for their primary winter predators, sea ducks, including surf scoters Melanitta perspicillata and Barrow's goldeneyes Bucephala islandica. Higher levels of mussel depletion in farm habitats and strong associations of ducks with shellfish farms indicate that sea ducks responded to this novel, profitable prey resource. Our results support recent research that indicates that artificial structures introduced into coastal areas create novel marine habitats that can support unique communities of epibiota. That sea ducks appear to profit from the introduction of aquaculture structures is evidence of a positive effect of anthropogenic modifications in a coastal environment.

The rules of engagement: how to defend against combinations of predators

Studies of inducible defenses have traditionally examined prey responses to one predator at a time. However, prey in nature encounter combinations of predators that should force them to produce phenotypic compromises. We examined how snails (Helisoma trivolvis) alter their phenotype in the presence of three different predator species that were presented alone and in pairwise combinations. When snails were exposed to each predator alone, they formed predator-specific defenses that reflected the differences in each predator's foraging mode. When snails were exposed to pairwise combinations of predators, their phenotype was dependent on their ability to detect each predator, the risk posed by each predator, and the effectiveness of a given defense against each predator. Consequently, responses to combined predators were typically biased towards one of the predators in the pair. This suggests that prey facing combined predators do not form simple intermediate defenses and, as a result, may experience enhanced mortality risk when they encounter natural predator regimes.

Population cycles of lemmings near Barrow, Alaska: a historical review

Current hypotheses regarding the causes of population cycling of brown lemmingsLemmus trimucronatus (Richardson, 1828), developed during long-term studies from 1950–1974. We maintain that three factors largely determine the timing and amplitude of population cycles in brown lemmings. First, a basic interaction between lemmings and vegetation sets the stage because dense populations of lemmings severely damage the vegetation, at which point lemming populations decline and remain low until the vegetation recovers. Second, opportunistic predators, mainly jaegers and owls, assemble as the snow melts during peak years and drive already declining populations to extremely low densities. Weasels are effective predators under the snow, but they appear irregularly. If weasel populations increase early in the cycle, lemming populations that normally increase dramatically during the winter in a peak year can be decimated before the snow melts. Finally, both wet summers that result in extensive flooding of the preferred habits of lemmings and freezing rains or winter thaws that cause ice formation reduce food availability, disrupt the cycle and extend the period between peak densities. Numerous observations, experimental results and simulation models support these views. Similar results regarding the importance of the available food supply, particularly in winter, and of the predation regime also have been reported for arvicoline populations at lower latitudes.

Predator regime influences innate anti‐predator behaviour in the freshwater gastropod Lymnaea stagnalis

Summary1. Predation incurs high fitness costs in aquatic organisms either through direct consumption or through avoidance responses that reduce time for activities such as feeding and reproduction. Hence, avoidance responses of aquatic organisms should vary to match closely the predation threat in their environment.2. The freshwater gastropod Lymnaea stagnalis occurs in a variety of environments which vary in the presence or absence of predatory fish. We used naïve snails reared from six populations of this species experiencing different predator regimes (three co‐occurring with molluscivorous fish and three without) to assess whether populations differed in the type and degree of their avoidance behaviours. Innate behavioural responses to four treatments (control, conspecific alarm cues, fish kairomones and fish kairomones paired with alarm cue) were compared in laboratory trials.3. The primary anti‐predator behaviour of L. stagnalis in response to fish kairomones was to crawl out of the water rather than seek refuge under water. This response was strongest when fish kairomones were paired with alarm cues, and varied depending on population origin; snails reared from populations co‐occurring with predatory fish showed a stronger response than those raised from populations not experiencing such predators. In addition, populations co‐occurring with predatory fish responded to the fish kairomones presented alone.4. Our findings suggest that the degree of innate anti‐predator behaviour shown by L. stagnalis, in terms of both the level of risk to which it responds and the degree of response, varies depending on the predator regime experienced by field populations. Together with previous work on cue association, this demonstrates that this gastropod is able to match its avoidance behaviour very closely to short and long term predation threats within its habitat.

Change in phenotypic plasticity of a morphological defence in Daphnia galeata (Crustacea: Cladocera) in a selection experiment

Some water fleas Daphnia change their head morphology to reduce predation risk in response to chemical substances (kairomones) released from larvae of the invertebrate predator Chaoborus (Insecta: Diptera). We tested for evidence of the costs associated with elongation of the head spine in Daphnia galeata and the consequences of these costs on the inducibility of head spine elongation in predictable and unpredictable environments. We exposed D. galeata in outdoor experimental ponds to conditions under which predation pressure by Chaoborus larvae and the concentration of kairomones from this predator were controlled for about 70 days. In the laboratory, we then used Daphnia clones collected from the outdoor ponds to investigate the inducibility of head spine formation in response to Chaoborus kairomones. The inducibility of head spine formation increased in D. galeata from the ponds that had contained both predators and kairomones, whereas in water fleas from the ponds containing only kairomones the plasticity (inducibility) of head spine formation decreased compared with that in the control ponds. These results suggest that the production of a defensive head spine, its phenotypic plasticity, or both entail some costs. Contrary to our predictions, exposure to Chaoborus kairomones in the laboratory resulted in head lengths that were not significantly different among any of the clones from the three outdoor treatments. We found no evidence for costs associated with head spine elongation in terms of fecundity, time to maturity, or intrinsic rate of natural population increase. Average within-clone partial correlations calculated for head length and intrinsic rate of natural population increase, corrected for body length, were not significantly negative, indicating no cost of defence. This was probably because food conditions in the laboratory were so good that the costs of defence could not be detected. Furthermore, community-level changes, such as changes in food conditions caused by manipulation of the predation regime in the outdoor ponds, might have worked as selection pressures and confounded the results.

Predation of a cave fish (Poecilia mexicana, Poeciliidae) by a giant water‐bug (Belostoma, Belostomatidae) in a Mexican sulphur cave

Abstract 1. Caves are often assumed to be predator‐free environments for cave fishes. This has been proposed to be a potential benefit of colonising these otherwise harsh environments. In order to test this hypothesis, the predator–prey interaction of a belostomatid (predator) and a cave fish (prey) occurring in the Cueva del Azufre (Tabasco, Mexico) was investigated with two separate experiments.2. In one experiment, individual Belostoma were given a chance to prey on a cave fish, the cave form of the Atlantic molly (Poecilia mexicana), to estimate feeding rates and size‐specific prey preferences of the predator. In the other experiment, population density of Belostoma was estimated using a mark–recapture analysis in one of the cave chambers.3. Belostomatids were found to heavily prey on cave mollies and to exhibit a prey preference for large fish. The mark–recapture analysis revealed a high population density of the heteropterans in the cave.4. The absence of predators in caves is not a general habitat feature for cave fishes. None the less predation regimes differ strikingly between epigean and hypogean habitats. The prey preference of Belostoma indicates that cave‐dwelling P. mexicana experience size‐specific predation pressure comparable with surface populations, which may have implications for life‐history evolution in this cave fish.

ECOLOGICAL SPECIATION IN GAMBUSIA FISHES

Although theory indicates that natural selection can facilitate speciation as a by-product, demonstrating ongoing speciation via this by-product mechanism in nature has proven difficult. We examined morphological, molecular, and behavioral data to investigate ecology's role in incipient speciation for a post-Pleistocene radiation of Bahamas mosquitofish (Gambusia hubbsi) inhabiting blue holes. We show that adaptation to divergent predator regimes is driving ecological speciation as a by-product. Divergence in body shape, coupled with assortative mating for body shape, produces reproductive isolation that is twice as strong between populations inhabiting different predator regimes than between populations that evolved in similar ecological environments. Gathering analogous data on reproductive isolation at the interspecific level in the genus, we find that this mechanism of speciation may have been historically prevalent in Gambusia. These results suggest that speciation in nature can result as a by-product of divergence in ecologically important traits, producing interspecific patterns that persist long after speciation events have completed.

10 000 years later: evolution of body shape in Haida Gwaii three‐spined stickleback

The body shape of 1303 adult male three‐spined sticklebackGasterosteus aculeatusfrom 118 populations on Haida Gwaii archipelago off the mid‐coast of British Columbia was investigated using discriminant function analysis on partial warp scores generated from 12 homologous landmarks on a digital image of each fish. Results demonstrated geographical differences in adult body shape that could be predicted by both abiotic and biotic factors of the habitat. Populations with derived shape (CV1−), including thick peduncles, posterior and closely spaced dorsal spines, anterior pelvis, small dorsal and anal fins, were found in small, shallow, stained ponds, and populations with less derived shape (CV1+), with small narrow peduncles, anterior and widely spaced dorsal spines, posterior pelvis, large dorsal and anal fins were found in large, deep, clear lakes. This relationship was replicated between geographic regions; divergent mtDNA haplotypes in lowland populations; between predation regimes throughout the archipelago, and in each geographical region and between predation regimes in lowland populations monomorphic for the Euro and North American mtDNA haplotype. There were large‐bodied populations with derived shape (CV2−), including small heads and shallow elongate bodies in open water habitats of low productivity, and populations with smaller size and less derived shape (CV2+), with large heads and deeper bodies in higher productivity, structurally complex habitats. This relationship was replicated between geographic regions, and partially between divergent mtDNA haplotypes in lowland populations. Field tests for phenotypic plasticity of body shape suggest that <10% of the total variation in body shape among populations throughout the archipelago can be attributed to plasticity.

Taxon‐specific reaction norms to predator cues in a hybridDaphniacomplex

Summary1. Previous studies have shown that interspecific hybridisation is common among taxa from theDaphnia galeata/hyalina/cucullataspecies complex. We investigated the influence of predator kairomones on the morphology and life histories of nine clones belonging to three taxa (pureD. galeata, F1hybrids betweenD. galeataandD. hyalina, and backcrossedD. hyalina) of this species complex. Predators exerting positive (fish) and negative (Chaoboruslarvae) size‐selective predation were tested.2. The most responsive traits were size at maturity and size of neonates. Despite large between‐clone variation, discriminant analysis revealed that the three taxa were distinct from each other in key life‐history traits. F1hybrids did not react in an intermediate way compared to the other taxa: the multivariate distances between F1hybrids and either taxon were larger than between pureD. galeataand backcrossedD. hyalina.3. The average plasticity (calculated across all traits) was similar for all three taxa. With regard to the size at maturity and neonate body size, the strength of the response was a function of the intrinsic values of these traits expressed in the control. For example, for size at maturity, smaller individuals showed a significantly stronger reaction toChaoboruskairomones than larger ones.4. Finally, we monitored seasonal changes in body size, egg number and population density of pureD. galeataand F1hybrids in Greifensee (Switzerland). The two taxa experienced similar seasonal changes in body size but, on some sampling dates, they differed in mean egg number. The observed seasonal changes inDaphniabody size were consistent with what would be expected if the predator assemblage shifted from fish toChaoborusover the course of the summer. The fluctuations in the frequencies ofDaphniataxa, however, were not related to seasonal variation inDaphniabody size.5. Experimental data suggest that temporally heterogeneous predation regimes might be an important condition stabilising the co‐occurrence ofDaphniahybrids with parental taxa. Predation regimes, however, cannot solely explain dynamic changes in taxon frequency in Greifensee.

Trophic heterogeneity in salt marshes of the northern Gulf of Mexico

Predator-prey interactions in salt-marsh ecosystems are driven primarily by interactions among tidal dynamics, local physiography, and macrophyte density. Distinct seaward-to-landward predation gradients have been described for the continuous and expansive meadows of Spartina alterniflora on the Atlantic coast of the United States. In the northern Gulf of Mexico, Juncus roemer- ianus dominates and Spartina is generally limited to fringing bands or disjunct patches in low-lying areas. It is not known whether predation regimes vary consistently among subhabitats in these dis- junct marshes. We investigated whether small-scale variations in topography and habitat structure produce persistently distinguishable predation regimes among marsh patches in coastal Alabama. Each of our study sites was representative of the principal subhabitats found within continuous Spartina meadows: vegetation bordering open water, tidal creeks within the marsh, and interior sub- habitat. We assessed a strong trophic interaction in these subhabitats: predation pressure exerted by the blue crab Callinectes sapidus on the periwinkle Littoraria irrorata. The distribution of sublethal repairs in Littoraria shells demonstrated that attacks by Callinectes were randomly inflicted, irre- spective of attack frequency. The occurrence of sublethal shell repair was positively related to the frequency of predatory attacks on experimentally tethered snails, the abundance of crabs, and the degree of antipredatory architectural defense in the snail shells. Among-site differences in shell repair and architectural defense were related to topography and habitat structure, and these differ- ences persisted over multiple seasons and years. Physical variations thus maintain strong, persistent predation regimes among subhabitats in disjunct Spartina marshes.

Naiveté and an aquatic–terrestrial dichotomy in the effects of introduced predators

There is much evidence that suggests that freshwater systems are more sensitive to introduced predators than are terrestrial or marine systems. We argue here that this dichotomy reflects widespread naiveté toward introduced predators among freshwater prey. Continental terrestrial animals are seldom naive toward novel predators owing to the homogenizing effects of historical biotic interchanges. Comparable biotic interchanges might have also precluded prey naiveté in most marine systems. By contrast, freshwater systems exhibit persistent large- and small-scale heterogeneity in predation regimes. This heterogeneity promotes naiveté at multiple spatial scales in freshwater prey, thereby producing a systemic vulnerability to introduced predators that is not seen in continental terrestrial or marine systems.

Life-history phenotypes in a live-bearing fish Brachyrhaphis episcopi living under different predator regimes: seasonal effects?

Several key life-history attributes in a tropical live-bearing fish, Brachyrhaphis episcopi, have previously been shown to differ between populations that co-occur with large predatory fish (Characin sites) and those that do not (Rivulus sites). Here we show that differences between Characin and Rivulus localities are also repeatable over time; patterns observed in the wet season also persisted during the dry. Both sexes reached maturity at a smaller size at Characin sites. Although there was no difference in fecundity between larger females living in different predator communities, smaller females at Characin sites produced more offspring. Females also produced smaller offspring at Characin localities. These differences are remarkably similar to those reported in two other species of live-bearing fish, B. rhabdophora and Poecilia reticulata suggesting possible convergent adaptation in life-history strategies due to predator-mediated effects or correlates thereof. We also found seasonal changes in life-history traits that were independent of predator community. In the wet season, mature males were larger, females allocated more to reproduction, and offspring mass was also greater. The results of our study generate testable predictions using B. episcopi to further our understanding of life-history evolution.

Flexible architecture of inducible morphological plasticity

1. Predator-induced morphological defences are produced in response to an emergent predator regime. In natural systems, prey organisms usually experience temporal shifting of the composition of the predator assemblage and of the intensity of predation risk from each predator species. Although, a repetitive morphological change in response to a sequential shift of the predator regime such as alteration of the predator species or diminution of the predation risk may be adaptive, such flexible inducible morphological defences are not ubiquitous. 2. We experimentally addressed whether a flexible inducible morphological defence is accomplished in response to serial changes in the predation regime, using a model prey species which adopt different defensive morphological phenotypes in response to different predator species. Rana pirica (Matsui) tadpoles increased body depth and tail depth against the predatory larval salamander Hynobius retardatus (Dunn); on the other hand, they only increased tail depth against the predatory larval dragonfly Aeshna nigroflava (Martin). 3. Rana pirica tadpoles with the predator-specific phenotypes were subjected to removal or exchange of the predator species. After removal of the predator species, tadpoles with each predator-specific phenotype changed their phenotype to the nondefensive basic one, suggesting that both predator-specific phenotypes are costly to maintain. After an exchange of the predator species, tadpoles with each predator-specific phenotype reciprocally, flexibly shifted their phenotype to the now more suitable predator-specific one only by modifying their body part. The partial modification can effectively reduce time and energy expenditures involved in repetitive morphological changes, and therefore suggest that the costs of the flexible morphological changes are reduced.

Disentangling the selective factors that act on male colour in wild guppies

The colour pattern of male guppies (Poecilia reticulata) is thought to evolve as a compromise between sexual selection (favouring conspicuousness) and natural selection (favouring crypsis). Underpinning this classic explanation is the observation that guppies living with dangerous fish predators are less colourful than guppies living without these predators. However, high fish‐predation sites are generally farther downstream than low fish‐predation sites, and so may also differ in physical habitat features related to stream size, as well as in the abundance of predatory prawns (Macrobrachium crenulatum). The goal of our study was to disentangle the effects of fish predation on colour evolution from the potential effects of physical habitat features and predation by prawns. We collected 20 male guppies from each of 29 sites in two Trinidadian rivers. We then quantified the colour pattern of these fish; each spot was measured for size and assigned to a colour category. For each site, we determined the fish predation regime and quantified stream size, water colour, canopy openness, and prawn abundance. We then used regressions to assess the relative importance of these factors in explaining variation in guppy colour. Supporting previous work, the presence of predatory fishes was the most important explanatory variable for many components of colour pattern. Physical habitat features explained some of the remaining variation, but in inconsistent ways between the two rivers. The abundance of predatory prawns also explained variation in male colour. Our results suggest that predatory fishes impose the strongest selection on the colour pattern of male guppies but that other factors are also important.