Predation Regimes Research Articles

Breeding habitat selection and larval performance of two anurans in freshwater rock‐pools

I studied breeding habitat choice of common toad Bufo bufo and common frog Rana temporaria in 221 freshwater rock‐pools on 15 small islands in the southwestern coast of Finland. I monitored tadpole growth rate in a number of rock‐pools differing in size, competitors and predator regime. Furthermore, I carried out a short‐term field experiment to investigate the effects of different predators on larval survival. Rana bred in pools of virtually all sizes, although the very smallest ones were usually avoided. A logistic regression analysis showed that the amount of aquatic macrophyte vegetation and pool surface area were the most important pool characters for Rana. Bufo preferred the largest pools, and pool surface area was by far the most important habitat variable. Rana avoided pools with the lowest pH. but was more common than expected at pools with pH around 6. In Bufo such an effect was not found, but this may be due to relatively low number of pools occupied by Bufo. In Rana there was a positive correlation between pool area and tadpole body length in early June, but two weeks later this relationship was not significant. In Bufo tadpole body size was not significantly affected by pool area. Presence of predators or presence of the other tadpole species did not affect growth or tadpole body size in either Rana or Bufo. A short‐term experiment in wading pools indicated that both species suffered heavy mortality in the presence of a diving beetle larva. In the presence of predatory fish, mortality of Bufo did not differ from controls, whereas mortality was high among Rana tadpoles. It appears that although predators prey heavily on Rana tadpoles, they do not exclude Rana from larger rock‐pools. However, it is not evident from this study why Bufo avoids smaller pools.

Elevated predation risk changes mating behaviour and courtship in a fiddler crab

The fiddler crab, Uca beebei, lives in individually defended burrows, in mixed-sex colonies on intertidal mud flats. Avian predation is common, especially of crabs unable to escape into burrows. Mating pairs form in two ways. Females either mate on the surface at their burrow entrance ('surface mating') or leave their own burrow and sequentially enter and leave ('sample') courting males' burrows, before staying in one to mate underground ('burrow mating'). We tested whether perceived predation risk affects the relative frequency of these mating modes. We first observed mating under natural levels of predation during one biweekly, semi-lunar cycle. We then experimentally increased the perceived predation risk by attracting grackles (Quiscalus mexicanus) to each half of the study site in two successive biweekly cycles. In each experimental cycle, crabs were significantly less likely to mate on the side with more birds. Moreover, on the side with elevated predation risk, the number of females leaving burrows to sample was greatly reduced relative to the number of females that surface-mated. Males waved less and built fewer mud pillars, which attract females, when birds were present. We discuss several plausible proximate explanations for these results and the effect of changes in predation regime on sexual selection.

Demography of a natural population of Daphnia retrocurva in a lake with low food quality

The hypothesis was tested that Daphnia exhibit low population recruitment in a lake with phosphorus (P)-deficient food, where Daphnia populations failed to increase in response to greatly lowered minnow density. Egg ratio analysis was performed on Daphnia retrocurva from L110 of the Experimental Lakes Area, Ontario, in 1994. L110 has high food abundance (seston carbon (C) - 100 uM C), but the seston is P deficient (C:P atomic - 600). Chrysophytes dominated the algal community. The fish community in this lake was manipulated in 1993 and 1994 by the addition of northern pike, Esox lucius. Zooplanktivorous minnows were greatly reduced after the piscivore addition, but the expected increase in abundance of the Daphnia to this altered predation regime was not observed. If food quality constrains the response of the Daphnia to changed predation, there should be low recruit- ment in the relatively sparse Daphnia population in this lake. Birth rates estimated by standard egg ratio analysis were <0.1 day1 for most of the sample period. In comparison to annual averages from the literature, recruitment in LI 10 was moderately, but not dramatically, low. Daphnia exhibited pronounced 'normal' vertical migration (up at night, down during the day) all year, and a strongly declining size at first reproduction through the season. Population density and birth rates seemed to show much less short-term change than previously observed in other lakes. Although the demo- graphic predictions for food quality constraints seemed clear, in situ demography unfortunately neither supported nor strongly rejected the overall hypothesis of food quality limitation in this lake with very high C:P ratios. Possibly, direct demographic effects of low food quality will be difficult to observe in nature.

Male display rate reveals ejaculate characteristics in the Trinidadian guppy,Poecilia reticulata.

Previous work (Reynolds and Gross 1992) has demonstrated that mate choice enables female guppies, Poecilia reticulata , to obtain heritable benefits (‘good genes’) for their offspring. It is not yet known whether males also signal their functional fertility, that is, their viability as fathers, to female guppies. Our study tested the hypothesis that a male9s behaviour reveals characteristics of his ejaculate. We uncovered a strong correlation between display rate and sperm number in male guppies derived from two wild Trinidadian populations. This result indicates that information on the functional fertility of potential mates is available to females. However, our investigation also found a significant relationship between the frequency of sneaky mating and sperm number. Female guppies in wild populations, particularly those experiencing a high predation regime, are constantly subjected to sneaky mating attempts. As the males responsible for these sneaky matings have highest reserves of sperm they may have the capacity to undermine female choice. The implications of these findings for sperm competition are discussed.

Behavioural response in plants: adjustment in algal recruitment induced by herbivores

Behavioural responses to chemical cues are common among animals, whereas there is still intense debate as to whether plants are able to detect environmental information and adjust their behaviour accordingly. Here, I report that several freshwater algal species respond to the presence or absence of grazers in the water column by regulating their recruitment rate from sediment to water. In lakes, as well as in controlled laboratory experiments with low abundances of grazers, recruitment of certain flagellated algal species was high, whereas recruitment was negligible when grazer abundances were high. Hence, certain plants equipped with locomotion organelles can use cues released from herbivores to adjust the timing of recruitment from the 'seed-bank', thereby reducing the exposure to grazing. Such an adaptation may have important consequences for dominance and temporal succession in algal communities. In an evolutionary context, this study shows that consumer-avoidance behaviour is not an adaptation exclusive to animals.

Variable Predation: Effects of Whelks on a Mid‐Intertidal Successional Community

In most habitats and ecosystems, predation varies significantly over space and over time. While several studies have demonstrated the effects of varying predation intensities, the effects of varying frequencies of predation have not been addressed explicitly. Here, I studied the impact of variable predation by whelks on a mid—intertidal successional community at a wave—exposed environment on the coast of Oregon. Densities of whelks were monitored in fixed—position quadrats for 34 mo, permitting an estimation of the natural spatial and temporal variation in predation by whelks. Two simultaneous cage experiments were then conducted for a period of 25 mo. One experiment evaluated the effect of prolonged exclusion of invertebrate predators on the sessile community. The other experiment evaluated the effects of the intensity and the temporal frequency of predation by whelks by manipulating both the density and presence of whelks inside cages. Three density levels were combined with three temporal patterns of predation (constant predation, medium and low frequency) in an orthogonal design to create nine different predation regimes. The replicated design allowed me to separate the effects of these two components of predation. The densities of the two whelk species present in the study site, Nucella canaliculata and N. emarginata, were highly correlated over time and varied greatly within and among years. Some areas of the site had whelks present most of the time (high frequency), while other areas were rarely visited. The frequency at which whelks were observed in a given area was uncorrelated with the yearly mean density, which contributed to the within—habitat variability in predation regimes by whelks. A suite of direct and indirect effects were observed following the permanent exclusion of invertebrate predators, notably, a rapid increase in the cover of the bay mussel Mytilus trossulus and a slow and small increase in the cover of gooseneck barnacles and the California mussel Mytilus californianus. Temporally variable predation (medium and low frequencies) produced community compositions different from those observed under a constant predation regime or predator exclusions. In general, individual species responses to variable predation could not be predicted from knowledge of the overall effect of predators obtained in the permanent exclusion experiment, nor from the results observed under different intensities and constant predation. Similarly, the actual number of predation days, estimated from the density and number of days whelks were in the cages, was not correlated with the mean cover of species. These results support the hypothesis that temporal frequency is an important component of predation with distinctive effects on intertidal prey communities. Both the ability of some prey to escape predators by reaching a large size and the temporal pattern of prey recruitment seemed important in determining the effect of variable predation on individual prey, but mechanistic understanding of the responses was complicated by the existence of many indirect effects. While temporally variable predation did not significantly increase spatial variability in prey abundance, constant predation regimes tended to reduce this variability over the course of succession. Temporal variability in predation by whelks can have distinctive effects on prey, create distinctive community compositions, and affect successional paths in this intertidal community. Temporal variability in predation is probably an important, yet poorly understood cause of spatial heterogeneity in most ecosystems.

Factors related to aggressive nest protection behaviour: a comparative study of Holarctic waders

Data on 12 factors presumed to influence the distribution of aggressive nest defence in 111 species of waders (incubation-sharing by the parents, number of parents present near the nest, incubation time, nest habitat, breeding latitude, body mass, wing loading, wing structure, detectability on the nest, predator regime, coloniality and alternative prey) were collected from literature and field researchers. Body mass and number of parents present on the nest territory (within response range when avian predators appear) explain 50% of the variation in aggressive defence behaviour. The results support the notion that ecological conditions like predation pressure are important in shaping wader parental care systems, with implications for mating systems. Altogether, the investigated factors explain around 70% of the variation in the samples. Future research on the level of individuals is suggested in order to explain the remaining variation.

Interactions between fish, grazing invertebrates and algae in a New Zealand stream: a trophic cascade mediated by fish-induced changes to grazer behaviour?

Experiments in laboratory stream channels compared the behaviour of Deleatidium mayfly nymphs in the absence of fish with that in the presence of either native common river galaxias (Galaxias vulgaris Stokell) or introduced brown trout (Salmo trutta L.). Galaxias present similar predation risks to prey during day and night but are more active at night. Whereas, trout present a higher predation risk during the day. Deleatidium maintained a fixed nocturnal drift periodicity that is characteristic of streams containing visually feeding fish regardless of the nature of the predation regime presented in the laboratory. However, the number on the substratum surface, and therefore able to graze algae, was lower when fish were present than when they were absent. The number was lower during the day in the presence of trout, when they present the highest predation risk, and lower during the night compared to the day in trials with galaxias when galaxias activity disturbs Deleatidium from the substratum. Increases in the probability of Deleatidium leaving a patch, reductions in the proportion of mayflies on high quality patches and reductions in the distance travelled from refuge also reflected variations in the predation regime. Similar differences in positioning were observed under the same predation regimes in in situ channels in the Shag River and these were associated with differences in algal biomass. Algal ash-free dry mass (AFDM) and chlorophyll a (chl a) were higher on the tops of cobbles when fish were present. Fish also affected the biomass and the distribution of algae on cobbles as AFDM and chl a were higher on the sides of cobbles from channels with trout compared to those with galaxias. Changes in grazing behaviour, caused by predator avoidance, are likely to have been responsible for differences in algal biomass because no significant differences were detected between treatments in the biomass of Deleatidium or of total invertebrates.

Female mate choice under predation risk in the guppy

Sexual selection, and thus the evolution of both female mating preferences and preferred male traits, may be constrained by costs associated with mate choice. Recent theoretical models predict that female preference should decrease with increasing costs of mate choice such as predation risk. This general hypothesis was tested experimentally by presenting individual female guppies, Poecilia reticulata, originating from two Trinidadian populations with different predation regimes, with a choice of paired males (differing mainly in colour pattern) as potential mates in both the absence and presence of a cichlid fish predator that naturally co-occurs in one of these populations. Moreover, any reduction in female preference under risk was predicted to be positively correlated with the level of predation intensity occurring in their respective populations. In an experiment in which only the female could see the nearby predator, females from the high-predation population (Quaré River) significantly reduced both their overall level of sexual activity and their preference for a particular male (most commonly the more colourful male) in the presence of the predator. In contrast, the sexual activity level and mating preference of females from the low-predation population (Paria River) were unaffected by the apparent threat of predation. Observed changes in female sexual activity level and mating preference could not have been mediated by any change in male behaviour when the predator was present, because the males could neither see or smell the predator nearby. In a corollary experiment in which both males and females from the risk-sensitive Quaré River population could freely interact with one another and see the predator, females significantly reduced their preference for the more brightly coloured male in the presence of the predator, irrespective of predator-mediated changes in male courtship behaviour. These results are best explained by a reduction in female preference under increased apparent risk of predation, and are consistent with the general hypothesis that female mate choice in the guppy is potentially costly in terms of an increased risk of mortality due to predation and that females from different populations are differentially sensitive to this risk when assessing and choosing potential mates. Therefore, predators may exert direct selection on female mate choice in certain natural populations of the guppy.

Impacts of an introduced predatory fish on mayfly grazing in New Zealand streams

The replacement of native common river galaxias (Galaxias vulgaris Stokell) by introduced brown trout (Salmo trutta L.) in many streams of the Taieri River system, New Zealand, has altered the predation regime for Deleatidium mayfly nymphs. Brown trout present a higher predation risk to mayfly prey during the day than at night but common river galaxias present similar risks both day and night. To determine whether this alteration has changed mayfly grazing behavior, we investigated the diel gut fullness of Deleatidium nymphs in five galaxias streams and five trout streams. Gut fullness was measured by the fluorescence of algal pigments extracted from Deleatidium guts. Nymphs from trout streams generally had fuller guts at night, whereas nymphs from galaxias streams tended to have more in their guts during the day or similar amounts both day and night. The difference reflects the high predation risk presented by brown trout during the day, restricting mayfly access to the algae‐rich upper surfaces of stones. These results indicate that the influence of predatory fish on mayfly grazing is detectable at a large spatial scale in the Taieri River system.

Contrasting predation risks presented by introduced brown trout and native common river galaxias in New Zealand streams

Alterations in the predation risk affecting macroinvertebrates in streams of the Taieri River system of New Zealand were assessed following the replacement of native common river galaxias (Galaxias vulgaris) in many sites by introduced brown trout (Salmo trutta). In laboratory channels, galaxias foraged on mayfly nymphs from benthic positions; they searched for prey at night but stayed in cover during the day except when attacking prey. Trout foraged from positions in the water column during day and night. There were no diel differences in foraging by galaxias but trout had higher reaction distances and consumed more during the day. No diel pattern was found in trout stomach contents in the field, probably because of a nocturnal increase in prey availability. Trout and galaxias populations in the field consumed similar biomasses of aquatic prey. However, these experiments indicate there have been subtle changes in the predation regime. Trout relied on visual cues to capture prey so predation risk was higher during the day and larger prey items were more at risk. In comparison, galaxias relied more on mechanical cues to capture prey and predation risk was similar during day and night.

Predator‐Induced Morphological Defenses: Costs, Life History Shifts, and Maternal Effects in Daphnia Pulex

This study was designed to measure and separate the physiological costs of inducible defenses from life history trade—offs and maternal effects in the waterflea Daphnia pulex. Juveniles of D. pulex produce morphological changes ("neckteeth") and undergo life history shifts as defenses against predatory Chaoborus (phantom midge) larvae. These traits are induced by a chemical cue (kairomone) released by the predator. I performed life history experiments with and without Chaoborus kairomones at different food levels to quantify the induced changes and their potential physiological costs. The Daphnia clone used in this study also increased its body depth in response to the predator substance. Life history shifted toward a larger body size (both length and depth) and higher fecundity, which was balanced by an increased time to reach maturity and by increased adult instar durations. Reproductive effort was higher in the typical morph in the first adult instar, indicating resource allocation shifts towards growth in the protected morph. However, even in the absence of predation the chemically induced protected morph tended to show an increased intrinsic rate of population growth (r). The longer time to reach maturity was not a direct physiological cost of neckteeth production, but a trade—off for larger body size. The life history shifts are independent of neckteeth formation. Developmental mechanisms leading to life history changes occurred after neckteeth were induced and could thus be uncoupled from neckteeth formation and its direct costs. In this study no direct costs were found. Carbon incorporation rates for the two morphs, at high and low food, were not different. As a maternal effect, the large females of the induced morph produced larger neonates which, in turn, matured at a larger size. Morphological changes, life history shifts, and maternal effects acted in concert to form defenses against Chaoborus. This study shows that the often assumed high physiological costs resulting from the formation or maintenance of the defenses are not necessary to explain the evolution of inducible defenses. As morphological changes increase the visibility of Daphnia pulex, a fitness disadvantage can be caused by a changing predator regime (e.g., fish). The results of this study suggest that environments with changing predator selectivities favor the evolution of inducible defenses.

Behavioural and morphological changes in polymorphic Daphnia related to different predation regimes

Behavioural and morphological changes in polymorphic Daphnia related to different predation regimes

Population differences in the schooling behaviour of the Trinidad guppy,Poecilia reticulata: adaptation or constraint?

Populations of the guppy Poecilia reticulata in Trinidad vary markedly in their tendency to school. In many cases this variation in behaviour can be attributed to variation in the predation regime: guppies that co-occur with the pike cichlid, Crenicichla alta, spend more time schooling and form larger schools than their counterparts from low-risk habitats. However, the association between schooling tendency and predation risk is not ubiquitous. In this paper we document the behaviour of guppies from populations in two Trinidad drainages. Guppies from the (Lower) Aripo River (in the Caroni drainage) display well-coordinated schooling behaviour irrespective of whether they are observed in the wild or raised under standard conditions in the laboratory. By comparison, Oropuche River guppies (from the Oropuche drainage) show only a weak schooling tendency. The contrast between the two populations is apparent even in newborn guppies. As pike cichlids are abundant at both sites it seems unlikely that reduced predation risk can account for the weaker schooling of the Oropuche River fish. The behavioural differences in the two drainages are paralleled by considerable genetic divergence and we therefore consider the possibility of phylogenetic constraints on the evolution of schooling.

Evidence for a trade-off between defensive morphology and startle-response performance in the brook stickleback (Culaea inconstans)

It is generally believed that predation pressure may drive the evolution of long spines, a robust pelvic girdle, and a deep body in sticklebacks (Pisces: Gasterosteidae). However, the lack of such traits in environments under intense predation pressure suggests that there may be a limit to which these apparently defensive structures benefit sticklebacks. In some environments, well-developed defensive structures may not increase stickleback survival, but may actually reduce fitness if there is a cost associated with them. This paper focuses on a trade-off between defensive morphology and escape-response performance in the brook stickleback (Culaea inconstans). Our study of four populations of brook stickleback reveals that the population with the largest pelvic girdles and deepest bodies has a poorly developed escape response (i.e., small displacement, low maximum velocity, and low acceleration), while the population with the smallest pelvic girdles and shallowest bodies has a highly developed escape response. The two populations with intermediate defensive structures are intermediate in escape-response performance. Consideration of predation regimes in different environments may help us understand selection pressures that favor heavily versus poorly armored stickleback morphs.

The effect of experience on mate choice in the Trinidad guppy,Poecilia reticulata

Two experients were conducted to determine the effect of male color phenotype present during development on the mate choice of adult female guppies. Females were raised with either a colorful male, non-colorful male, or no male, and then measured for choice of a colorful or non-colorful male in a two-stimulus visual choice test. In the first experiment, adult females were measured for choice between the same male phenotypes used during the developmental exposure. Females raised with colorful males had significantly higher choice scores for colorful males than did females raised with non-colorful males or with no male. In the second experiment, an effect of developmental experience was observed when adult females were tested for choice with a general range of colorful and non-colorful males. However, this effect of experience during development was not detected when females were tested for choice between the same male phenotypes used during the developmental exposure. The predation regime of the source population, either high or low, showed no consistent effect on average female choice or on whether developmental experience changed female mate choice. Overall, these experiments show that experience with male phenotypes can affect the mate choice of adult guppies, but this effect was not observed under all developmental treatments or test conditions. Such an effect could significantly change the dynamics of the evolution of female preference due to sexual selection in the guppy.

Predator-Induced Cyclical Changes in Lateral Plate Frequencies of Gasterosteus

This study investigates ecological aspects to intrapopulation variability in the lateral plates of threespine stickleback (Gasterosteus aculeatus) at a coastal lake in western Canada. The frequency distribution of the plates, which was slightly skewed to the right and leptokurtic, varied spatially and seasonally. Cyclical frequency changes in plates were most pronounced on sub-adult size classes and these closely tracked (multiple r = 0.77) seasonal differences in the relative proportion of the two major predator groups, trout and diving birds. Trout predation was correlated with an increase in plate number while bird predation was correlated with a reduction in plate number. Such divergent selection pressures, which are probably common in natural populations, would account for the presence of multiple phenotypes and allow for rapid shifts in defensive morphology among different populations where predation regime differs.

Factors affecting the distribution of genetic variability in the guppy, Poecilia reticulata

Previous studies on Trinidadian guppies have shown an apparent association of genetic variability, expressed as mean heterozygosity (Ho) at allozyme loci, with river order: fish from lowland sites exhibit higher mean Ho than their upland counterparts. Detailed genetic and behavioural observations were undertaken in the present study by repeated sampling throughout two river courses to examine population heterogeneity. Results show that the predation regime mediated mating behaviour of upland and lowland populations in the wild is not as divergent as previous laboratory observations have suggested. Furthermore, genetic variation at the eight loci variable in Trinidadian populations (p100=0·13–O·88, H0=O·03–0·23) appears to bear little association with predation regime, but is related to sub‐structuring of populations by habitat features and geographic isolation. We therefore conclude that the observed patterns of genetic variability arise primarily as a consequence of stochastic as opposed to deterministic factors.

Interpopulation Variation in Mayfly Antipredator Tactics: Differential Effects of Contrasting Predatory Fish

Introduced brown trout (Salmo trutta) have replaced native common river galaxia (Galaxias vulgaris) as the principal predators in many streams in the Taieri River system, New Zealand. Brown trout and common river galaxias present prey with contrasting predation risks as galaxias forage mainly at night using mechanical cues and trout present a higher predation risk during the day by foraging using visual cues. To determine if this change has affected the behavior of a siphlonurid mayfly, Nesameletus ornatus, we compared the behavior of N. ornatus nymphs from three neighboring streams that have different fish predation regimes (trout, galaxias, fishless) when confronted with all possible predation regimes in the laboratory (trout, galaxias, no fish). N. ornatus from a trout stream were consistently nocturanally active whether trout, galaxias, or no fish were present. In contrast, when mayflies from streams without trout were confronted with trout, no consistent diel periodicities in their behavior were observed. However, when mayflies from stream without trout were tested with and without galaxias they altered their behavior according to the presence/absence of the native predator. The possibility that N. ornatus accumulates evolutionary experience of trout through adults flying between streams may be ruled out: mayflies with no possible experience of trout did not respond differently to those from streams without trout but with the possibility of migrating from trout streams close by. The presence of different predatory fish may have resulted in differential trade—offs between foraging and predator avoidance. The probability of mayflies leaving food patches was higher during the day in the presence of trout. In contrast, the probability was higher during the night in the presence of galaxias. Trout and galaxias were also associated with differential reductions in the number of mayflies on the substrate surface and the proportion of mayflies on food patches, with consequent effects on time spent foraging. These responses indicate that both the history of the prey population and the nature of the predation risk have considerable influence on antipredator behavior and indicate a possible important influence on stream communities of predatory fish through sublethal effects on prey behavior.

Habitat Choice in Breeding Seabirds: When to Cross the Information Barrier

The choice of breeding site is a key reproductive decision for long-lived seabirds. Individuals pioneering new sites face unknown risks (e.g., unfavourable predator regimes, climate), but potential breeders may derive information about reproductive opportunities from the presence of conspecifics, just as local enhancement is used to derive information about local feeding conditions. We suggest here the information barrier hypothesis: the presence of nesting birds may furnish cues about local breeding conditions (e.g., abundant food, safe places to nest); this information advantage may deter dispersal to new habitat, even though good breeding sites may be available elsewhere. By settling at an established site, individuals gain confidence that local conditions are favourable for breeding, whereas individuals pioneering new sites receive no such promise