Predation risk affects courtship and attractiveness of competing threespine stickleback males

The effect of predation risk and male-male competition on male courtship behaviour and attractiveness to females was studied in the threespine stickleback (Gasterosteus aculeatus) by presenting dummy or live females to solitary and competing males under different predation risks. In the presence of a predator, males decreased courtship activity. Different courtship components were, however, adjusted to different extents and in opposing directions to predation risk, probably because the single components may have varied in riskiness. The presence of a competing male decreased overall courtship activity, but increased the frequency of zigzags, suggesting zigzagging to be a competitive strategy against other males. In the presence of a predator male courtship activity was not affected by a competitor. Female mate choice correlated with the males' previous frequency of zigzags towards a dummy female. However, when a live female paid attention to a male, the male decreased zigzagging and instead increased leading and fanning behaviours, probably trying to attract the female to the nest to mate. Predation risk affected the attractiveness of males as females reduced their attention to a male when he faced a predator and reduced his courtship activity. As females instead increased their attention to a competing male that had increased his courtship activity, due to decreased competition, males clearly are balancing mating opportunities against predator avoidance. When males vary in their susceptibility to predators, predation risk may thus affect mating success of competing males. Received: 31 January 1997 / Accepted after revision: 15 April 1997     

Female behaviour mediates male courtship under predation risk in the guppy (Poecilia reticulata)

Previous work has shown that under elevated predation risk, male guppies (Poecilia reticulata) switch from courtship to less conspicuous coercive mating attempts. This behavioural transition is traditionally interpreted as a 'risk-sensitive' response that makes males less conspicuous to predators. However, predation risk leads to behavioural changes (such as schooling and predator inspection) in females that may result in coercive mating attempts being more profitable in high-risk situations. Here, we tested the hypothesis that the switch to coercive mating by male guppies in high-risk situations is mediated by adjustments in female behaviour, rather than directly by the predator. We used replicate models resembling a known guppy predator to simulate predation risk in wild-caught guppies from a high-predation population in Trinidad. Our results revealed that males performed proportionately more coercive mating attempts when presented with a female that had been exposed previously to a model predator compared to when males were paired with non-exposed females. Total mating activity (combined rates of courtship and forced mating attempts) did not differ significantly among the two treatment groups, indicating that overall mating activity is unaffected by predation risk. Importantly, when we subsequently presented both sexes concurrently with a predator model, total mating activity and the proportion of forced mating attempts remained unchanged in the high-risk treatment. Taken together, these results indicate that the transition from courtship to forced mating attempts under elevated predation risk is mediated by changes in female behaviour, which we suggest may favour the use of coercive mating under high predation risk.     

Effects of prey concentration,prey size,predator life stage,predator starvation,and season on predation rates of the carnivorous copepod Euchaeta elongata

Adult females of the large carnivorous copepod Euchaeta elongata Esterly were collected from 1977 to 1980 in Port Susan, Washington, USA. Predation rates of the adult females increased with increasing prey abundance when fed the following 4 sizes of copepods: adult females of Calanus pacificus (average prosome length [PL] of 2 650 μm), adults of Aetideus divergens (PL of 1 560 μm), adult females of Pseudocalanus spp. (PL of 1 060 μm), and nauplii of C. pacificus (PL of 410 μm). Saturation feeding levels were reached when adult females of the predator were fed the small adult copepod, Pseudocalanus spp. Maximum biomass ingested of this small copepod was more than the maximum amount ingested of the larger copepods. Predation rates of the predatory copepodids at Stages IV and V also increased with increasing concentration of the 1 060 μm (PL) prey. High feeding rates exhibited by both adults and copepodids at Stage V of the predator indicate their importance as sources of mortality on populations of small copepods. Ingestion efficiency E _i (prey wholly consumed [prey attacked]^-1) varied as follows: adults of E. elongata were more efficient than copepodids of E. elongata; adults were more efficient than copepodids when ingesting smaller prey; starved adults were more efficient than fed ones; and both adults and copepodids were more efficient at low food concentrations. For adults of E. elongata, there were no marked seasonal variations in predation or respiratory rates that would represent acclimatory responses; however, small adults obtained during winter were more efficient at ingesting prey than were the larger adults gathered in summer. This seasonal variation in the efficiency of ingestion may be a useful indicator of physiological state: high E _i values could indicate that predators are starving in winter, and low E _i values could indicate that predators are satiated in summer.     

Predator-induced female behavior in the absence of male incubation feeding: an experimental study

Parental care plasticity is critical to understanding the ecological and evolutionary influence of nest predation on life history strategies. In birds, incubation imposes a trade-off between the requirements of females (i.e., food) and egg requirements (i.e., heat and protection from predators). However, studies on this topic are rare and usually restricted to species where the male feeds the incubating female, relaxing her incubation costs. Males and females can reduce their activity at the nest to avoid detection by predators. However, females could follow two alternative antipredator strategies: to delay their return to the nest to avoid attracting attention from the potential predator or to return to the nest as soon as possible to enhance nest concealment. In this study, we manipulated the perceived risk of nest predation of incubating common blackbirds (Turdus merula), a species without incubation feeding, to study female behavioral changes induced by nest predation risk. We show experimentally that female blackbirds can reduce their nest visits in the situation with higher nest predation risk. In addition, we confirm that females significantly delay their return to the nest in the presence of a nest predator, contradicting the nest concealment hypothesis. However, our results could be interpreted as a passive antipredator response (to minimize clues given to predators) or as an active antipredator response (to search for predators to expel them from their territories).     

Predation of calanoid copepods on their own and other copepods’ offspring

Predation of eggs and nauplii by adult copepods is often used to explain unexpected death rates in population dynamics studies, but the phenomenon has been rarely investigated or quantified. Therefore, we studied the predatory feeding of adult females (Acartia clausi, Centropages hamatus, Centropages typicus, and Temora longicornis) on their own and other species’ eggs and young nauplii with different densities of single animal-prey, mixtures of animal-prey and in the presence of diatoms. All species preyed on eggs and nauplii of their own and all other species. Maximal egg predation varied between 7 and 64 eggs fem^?1 day^?1. Ingestion of Centropages spp. eggs was lowest, potentially due to the spiny egg surface. Maximal feeding rates on nauplii ranged from 5 to 45 nauplii fem^?1 day^?1. T. longicornis preferred eggs, when eggs and nauplii were offered together at the same densities, and the other predators selected for nauplii. At a diatom concentration of 60 μg C l^?1 predation on eggs by C. typicus was higher than without algae, whereas A. clausi and T. longicornis did not change their uptake of eggs. Feeding on nauplii in the presence of diatoms was again enhanced in C. typicus, and unaffected in A. clausi and C. hamatus. T. longicornis reduced its feeding on nauplii in the presence of diatoms. Calculated predation rates, using field abundances of predators and prey, suggest that predation of copepods on their own young stages may account for ca. 30 % of total mortality of young stages in North Sea copepod populations.     

Predators of juvenile sea urchins and the effect of habitat refuges

We evaluated the effects of potential predators from intertidal habitats on Strongylocentrotus purpuratus survival using laboratory experiments and assessed abundances of main predatory species along the Pacific coast of North America. The interactive effects of urchins’ and predators’ sizes in mediating predation were quantified. Habitat complexity (substrate pits, adult spine canopy) was manipulated to examine its effects on predation of most susceptible individuals (<14 mm). Pachygrapsus crassipes was identified as a major predator of urchins up to ≈30 mm. A positive effect of predator size on consumption of progressively larger urchins was detected, probably due to a mechanical limitation on crabs’ ability to consume large prey. Larger claws of males with respect to females of comparable sizes facilitated the handling of larger prey. Substrate refuges significantly reduced mortality on juvenile urchins. These results show that crab predation may be important in organizing intertidal communities, despite multiple ecological mechanisms promoting sea urchin survival.     

Predation affects alarm call usage in female Diana monkeys (Cercopithecus diana diana)

Diana monkeys produce acoustically distinct calls to a number of external events, including different types of predators. In a previous study, we found population-wide differences in male alarm call production in Taï Forest, Ivory Coast, and on Tiwai Island, Sierra Leone, mostly likely originating from differences in predator experience. In Taï Forest, leopards (Panthera pardus) are common but on Tiwai Island they have been absent for decades, while the predation pressure from crowned eagles (Stephanoaetus coronatus) has been similar. To further evaluate the impact of predator experience, we here analyse the vocal behaviour of female Diana monkeys in both habitats. Female Diana monkeys produce predator-specific alarm calls, alert calls and contact calls in response to predators, suggesting that their calls serve in a broader range of functions compared to males. Results showed that females produced the same call types at both sites, despite the differences in predator fauna. Regarding call usage, leopard alarm calls were extremely rare on Tiwai Island, but not in Taï Forest, whereas we found no differences in eagle alarm call production. When comparing response latencies, Tiwai females were slower to respond to both predators compared to Taï females. Finally, we found no habitat-specific acoustic differences in the alert and predator-specific alarm calls, but significant differences in frequency-based parameters of contact calls. Overall, our results suggest that ontogenetic experience can affect primate vocal behaviour in both usage and acoustic structure but that the way in which particular call types are affected may be closely linked to function.     

Fate of domoic acid ingested by the copepod <Emphasis Type="Italic">Acartia clausi</Emphasis>

Two important issues in the studies of harmful algae include ecological role of the toxic compounds and their fate through the food web. The aims of this study were to determine whether the production of domoic acid is a strategy evolved to avoid predation and the role of copepods in the fate of this toxic compound through the food web. The copepod Acartia clausi was fed with single and mixed cultures of the toxic diatom Pseudo-nitzschia multiseries and the non-toxic diatom Pseudo-nitzschia delicatissima. Ingestion rate as a function of diatom abundance was the same for the toxic and non-toxic Pseudo-nitzschia species, indicating no selective feeding behaviour against P. multiseries. The toxins ingested by the copepods did not affect mortality, feeding behaviour, egg production and egg hatching of the copepods. Copepods assimilated the 4.8% of the total domoic acid ingested. Although the amount of toxins daily detoxificated by the copepods was 63.6%, the copepods accumulated domoic acid in their tissues. We conclude that domoic acid is not toxic for copepods and, probably for this reason, this toxin does not act as feeding deterrent for copepods. However, even though the production of domoic acid has apparently not evolved to deter predation, copepods may play an important role on the fate of this toxic compound through the marine food web.     

Do mountain log skinks (<Emphasis Type="Italic">Pseudemoia entrecasteauxii</Emphasis>) modify their behaviour in the presence of two predators?

Prey often adopt antipredator strategies to reduce the likelihood of predation. In the presence of predators, prey may use antipredator strategies that are effective against a single predator (specific) or that are effective against several predators (nonspecific). Most studies have been confined to single predator environments although prey are often faced with multiple predators. When more than one predator is present, specific antipredator behaviours can conflict and avoidance of one predator may increase vulnerability to another. To test how prey cope with this dilemma, I recorded the behaviours of lizards responding to the nonlethal cues of a bird and snake presented singly and simultaneously. Lizards use specific and conflicting antipredator tactics when confronted with each predator, as evidenced by refuge use. However, when both predators were present, lizards refuge use was the same as in the predator-free environment, indicating that they abandoned refuge use as a primary mechanism for predator avoidance. In the presence of both predators, they reduced their overall movement and time spent thermoregulating. This shift in behaviour may represent a compromise to minimize overall risk, following a change in predator exposure. This provides evidence of plasticity in lizard antipredator behaviour and shows that prey responses to two predators cannot be accurately predicted from what is observed when only one predator is present.Communicated by W. Cooper     

Hunted hunters? Effect of group size on predation risk and growth in the Australian subsocial crab spider Diaea ergandros

A reduced predation risk is considered to be a major adaptive advantage of sociality. While most studies are concerned with non-predatory prey species, group-living predators are likely to face similar threats from higher-order predators. We studied the relationship between group size and predation risk in the subsocial crab spider Diaea ergandros by testing predictions from theoretical models including attack abatement as well as the formation of protective retreats. In a field survey, we found predatory clubionid spiders in 35 % of the D. ergandros nests and as predicted, nest size did not correlate with predator presence. In a subsequent laboratory experiment, we observed survival probability, nest construction activity and feeding behaviour including weight development between groups of different sizes as well as in the absence or presence of a predator. Large groups had an advantage in terms of survival and growth compared to smaller groups or single individuals. They also built significantly larger nests than smaller groups, supporting the idea of protective retreat formation being an adaptive benefit to group living. Even though clubionids did attack D. ergandros, they did not significantly affect overall mortality of D. ergandros. The feeding experiment showed that spiders fed on a larger proportion of flies in the presence of a predator. However, these groups gained significantly less weight compared to the control groups, indicating that the potential predators not only act as predators but also as food competitors, constituting a twofold cost for D. ergandros.     

Reproduction under predation risk in the sand goby,Pomatoschistus minutes,and the black goby,Gobius niger: the effect of age and longevity

Summary In aquarium experiments, the two marine gobiid fish species Pomatoschistus minutus and Gobius niger were allowed to build nests and to spawn in the presence and absence of a predator (cod, Gadus morhua); behind a glass wall the predator was kept where it could be clearly seen by the gobies and vice versa. P. minutus showed no difference in number of nests or number of spawnings in the different treatments; approximately half of the males built nests, and the females spawned in half of those nests. G. niger, on the other hand, responded differently to the simulated predation risk. No nests were built in sight of the predator, whereas in the absence of predators, half of the males built nests and received eggs. The G. niger individuals in this experiment were 2–3 years old. However, when comparing the reproduction of G. niger of different age in the presence of a predator, older individuals (4–5 years) spawned, whereas younger (2–3 years) did not. No difference in vulnerability towards predators was found between equal-sized P. minutus and G. niger. The optimal behavior during the breeding season must depend on prospects of survival, based both on maximal lifespan and vulnerability to predation.     

Bat predation and the evolution of leks in acoustic moths

Theories of lek evolution generally invoke enhanced mating success experienced by males signalling in aggregations. Reduced predation has also been acknowledged as a potential factor driving lek formation, but its role is more ambiguous. Although lekking is a complex behaviour, few empirical studies have investigated the role of both claims. We studied the potential pressures imposed by mating success and predation in an acoustic moth, Achroia grisella, in which males gather in leks and broadcast a calling song attractive to females. We exploited the ability to manipulate the distribution of singing males in laboratory arenas to create different-sized leks and tested female preferences for these aggregations. Because A. grisella are vulnerable to predation by bats while in flight and on the substrate, we also tested the responses of a potential predator, Rhinolophus ferrumequinum, a bat species that feeds on moths, to the experimental leks. We found that the per capita attractiveness of A. grisella males to females rose with increasing lek size. R. ferrumequinum also oriented toward experimental A. grisella leks, but this attraction did not increase at larger leks. Thus, a male’s per capita exposure to predation risk declined as more moths joined the lek. A. grisella males appear to benefit from advertising in larger leks in terms of both increased mate attraction and reduced predation risk. Our results support the idea that multiple factors operating simultaneously may maintain lekking behaviour.     

Threat-sensitive foraging by larval threespine sticklebacks (Gasterosteus aculeatus)

Summary The threat-sensitive predator avoidance hypothesis predicts that prey can assess the relative threat posed by a predator and adjust their behaviour to reflect the magnitude of the threat. We tested the ability of larval threespine sticklebacks to adjust their foraging in the presence of predators by exposing them to conspecific predators of various sizes and recording their foraging and predator avoidance behaviours. Larvae (<30 days post-hatch) displayed predator escape behaviours only towards attacking predators. At 3 weeks post-hatch larvae approached the predator after fleeing, a behaviour which may be the precursor to predator inspection. Larvae reduced foraging and spent less time in the proximity of large and medium-sized predators compared to small predators. The reduction in foraging was negatively correlated to the predator/larva size ratio, indicating that larvae increased their foraging as they increased in size relative to the predator. We conclude that larval sticklebacks can assess the threat of predation early in their ontogeny and adjust their behaviour accordingly.Correspondence to: J.A. Brown     

Predation risk reduces male-male sexual competition in the Trinidadian guppy (Poecilia reticulata)

Because agonistic behaviour can increase an individual's risk of predation, natural selection should favour individuals that modify their behaviour in the face of predation hazard in ways that maximise fitness. We investigated experimentally the effects of an increase in the apparent risk of predation on male-male competition within mixed-sex shoals of the Trinidadian guppy (Poecilia reticulata). We show that males engaged in significantly fewer aggressive interactions with conspecific males in the presence of a fish predator. However, they continued to court and attempt copulations with females at the same rate irrespective of the level of predation risk. In comparison, under predation hazard, female guppies were less responsive sexually and avoided fewer male copulation attempts. Such predator-mediated changes in male-male agonistic interactions and female sexual responsiveness towards males have important implications for the mode and intensity of sexual selection within populations.     

Mating behaviour of Macrophthalmus hirtipes (Brachyura: Ocypodidae)

 We examined the mating behaviour of the New Zealand ocypodid crab Macrophthalmus hirtipes in the laboratory between February and June 1998. This species has a discrete breeding season. Mating and moulting were not linked and only intermoult females with mobile gonopore opercula were attractive to males. Allometry and compatibility of gonopods and gonopores of different-sized crabs was investigated. Under laboratory conditions, the opercula of intermoult females remained mobile on average for 11.4 d, but the duration of receptivity did not appear to be under female control. The operational sex ratio in the laboratory fluctuated greatly, but was always male-dominated. During the period of opercular mobility, females mated many times with several different males. Matings in the absence of burrows were relatively short (mean duration = 23 min, max. = 122 min) and the mating behaviour of M. hirtipes lacked courtship and mate-guarding. Males used a search-intercept method to acquire mates, with very low levels of intrasexual competition. There was no evidence of mate preference in M. hirtipes, and males spent just as long mating with ovigerous females as with non-ovigerous ones. Although M. hirtipes has ventral-type spermathecae, as do several other ocypodid crabs, it is unclear whether this promotes last-male sperm precedence. The role of burrows in modifying the mating behaviour of M. hirtipes in the field remains to be established. Received: 7 January 2000 / Accepted: 5 June 2000     

Loss of mating opportunities influences refuge use in the Iberian rock lizard,<Emphasis Type="Italic"> Lacerta monticola</Emphasis>

Because time spent in refuge may be costly if prey lose opportunities to forage, fight, or mate, prey allow predators to approach closer before beginning to flee when opportunity costs are high. Because the same opportunity costs may apply to refuge use as to escape, prey should make similar trade-offs between risk of emerging and cost of remaining in refuge. In the Iberian rock lizard, Lacerta monticola, we studied the effects of sex, reproductive season, speed of predator approach, and potential loss of mating opportunities on time spent in refuge following simulated predatory attacks. Lizards of both sexes adjusted refuge use to the level of risk by spending more time in refuge when approached rapidly than slowly. Females remained in refuge for equal times in the mating and postreproductive seasons, but males emerged sooner during the mating season, suggesting adjustment to a cost of lost opportunity to search for mates during the mating season. When a tethered female was nearby, males emerged from refuge earlier than if no female was present, indicating a trade-off between risk and mating opportunity. Approach speed affected emergence time when females were absent, but not when a female was present. Approach speed did not affect the probability that, after emerging, a male would return to court the female. For males that courted females intensely (bit them) before entering refuge, approach speed did not affect latency to emerge, but males that courted less intensely emerged sooner if approached slowly than rapidly. These findings show that males adjust the length of time spent in refuge to both risk of predation and reproductive cost of refuge use.Communicated by A. Mathis     

Costs of courtship and mating in a sexually cannibalistic orb-web spider: female mating strategies and their consequences for males

The costs of courtship and mating may include increased risks of predation, the transmission of pathogens, and a loss of foraging opportunities. Thus, a female's decision to tolerate a courting male will depend upon how these costs offset the benefits of mating, which will depend on her reproductive and nutritional status. While these costs may be similar for mated and unmated females, the benefits of mating will be less for mated than virgin females. However, the cost of lost foraging opportunities may be higher for females with fewer nutritional reserves necessary for forming eggs. We examined how these costs and benefits influence the courtship and mating behaviour of male and female orb-web spiders, Argiope keyserlingi. In the field, females on webs that also contained a courting male intercepted fewer prey items per hour than females on webs without a male. In the laboratory, the presence of a courting male at the hub also attracted mantid predators to the web, increasing the risk of predation for both male and female. Staged mating experiments in the laboratory revealed that the frequency of female attacks and pre-copulatory cannibalism was greater among mated than virgin females. Feeding history did not affect aggression in virgin females but, among mated females, food-deprived spiders attacked and cannibalized males more frequently than sated females and only the latter ever remated. These differences in female behaviour influenced male mating strategies. Choice experiments demonstrated that males preferred to venture onto the silk threads of virgin rather than those of mated females. Similar patterns of mate selectivity were observed in the field; females with narrow abdomens attracted more males to the webs than females with broad abdomens, and copulations were observed more frequently among females with narrow abdomens. These smaller females are likely to be virgins that have recently molted. Males that preferentially mate with virgin females will not only avoid potentially fatal attacks but also obtain, on average, a higher fertilization success.     

Nitrate affects courting and breathing but not escape performance in adult newts

The increasing spread of contaminants in the environment affects the behaviour of individuals and can be predicted to modify population characteristics in the long run. It is thus crucial to investigate the effect of contaminants on fitness-related traits. Nitrate is a major pollutant that disrupts oxygen fixation and steroid metabolism and is expected to affect adult behaviour. In water breeding newts, reduced oxygen supply may increase predation risk by elevating surfacing rate and limiting the capacity to evade a predator. It may also reduce mating success by altering sexual behaviour. We assessed the effect of nitrate on fitness-related behavioural traits in male palmate newts Lissotriton helveticus. We measured courtship and breathing during sexual encounters and escape performance in exposed and non-exposed adults. Unexpectedly, exposed males courted females more often than control males. Body size and breathing rate were also positively related in control males but not in exposed males. Results only partially support the hypothesis of oxygen transfer disruption. Alternatively, exposed males seem to compensate their reduced olfactory attractiveness by decreasing surfacing and increasing courtship frequency. Surprisingly, nitrate did not affect escape performance possibly because anaerobic respiration supplies most of energy during unsustainable activity. Nitrate exposure altered time budget in exposed adults and shifted behavioural trade-offs between competing activities like breathing and courting. Ecological and evolutionary consequences, driven by changes on predation risk or sexual selection regimes, can be expected. This study calls for more attention on amphibian adult stages and the evolutionary response of populations in contaminated environments.     

Food and predators affect egg production in song sparrows

Although the possibility that food and predators may interact in limiting avian populations has long been recognized, there have been few attempts to test this experimentally in the field. We conducted a manipulative food addition experiment on the demography of Song Sparrows (Melospiza melodia) across sites that varied in predator abundance, near Victoria, British Columbia, Canada, over three consecutive breeding seasons. We previously showed that food and predators had interactive effects on annual reproductive success (young fledged per female). Here, we report the effects on egg production. Our results show that food limits the total number of eggs laid over the breeding season ("total egg production") and that interactive food and predator effects, including food effects on nest predation, determine how those eggs are "parceled out" into different nests. Food addition alone significantly affected total egg production, and there was no significant interannual variability in this result. At the same time, both food and predators affected the two determinants of total egg production: "clutch number" (total number of clutches laid) and average clutch size. Both clutch number and size were affected by a food x predator x year interaction. Clutch number was lower at low-predator locations because there was less nest predation and thus less renesting. Food addition also significantly reduced nest predation, but there was significant interannual variation in this effect. This interannual variation was responsible for the food x predator x year interactions because the larger the effect of food on nest predation in a given year, the smaller was the effect of food on clutch number; and the smaller the effect of food on clutch number, the larger was the effect of food on clutch size. Potential predator and year effects on total egg production were thus cancelled out by an inverse relationship between clutch number and clutch size. We suggest that combined food and predator effects on demography could be the norm in both birds and mammals.