Intruder Pressure Affects Territory Size and Foraging Success in Asymmetric Contests in the Water Strider Gerris lacustris

The theory of evolutionarily stable strategies (ESS) in asymmetric contests predicts that the propensity of an individual to expose itself to risk during contests depends on the individual's resource-holding-potential (RHP) and on the value of the disputed resource (V) for the individual compared with that for an opponent. If encounters of a territory owner with individuals of high RHP and high food demands (V) increase in frequency, one should expect a decrease in total aggressiveness of the territory owner, and in consequence a decrease of its territory size. Such a decrease should result in a lower amount of food consumed by the territory owner. Using natural variability in RHP and V in Gerris lacustris, I experimentally tested these predictions. The average prey item has higher value (V) for reproductive female water striders (which probably transform most of their food into eggs), than for nonreproductive females and for males. Because males are smaller, they have lower RHP than females, as RHP depends on size. Thus the reproductive females are the class of individuals of high RHP and high food demands (high V). Most nonreproductive females defend food-based territories. I observed two groups of water striders in a seminatural laboratory setting. As predicted, there was a negative correlation between the rate of encounter with reproductive females and size of the territory, and a positive correlation between territory size and number of Drosophila flies consumed by the owner. Territories were smaller in the group with high rates of encounter between territory owners and reproductive females. Territory owners caught the same number of Drosophila flies as non-territorial individuals in this group. In contrast, in the group with fewer encounters between territory owners and reproductive females, territories were larger, and territory owners gained more food than non territorial water striders.     

Basal song rate variation in male red-winged blackbirds: sound and fury signifying nothing?

Male red-winged blackbirds (Agelaius phoeniceus) vary substantiallyin how much they sing. We tested whether song rate reflectedthe male’s quality, the quality of his territory, or hisfrequency of interaction with potential competitors. Song ratedeclined with the seasonal decline in nest initiations, suggestingthat song is used to attract females. However, males with highersong rates did not obtain larger harems. This suggests thatfemales do not use male song rate to assess either male qualityor territory quality. If song rate signals male quality to malerivals, and if territory owners are of higher quality than floaters,then owners' song rates should be higher than those of floaters.However, when we removed territory owners temporarily, the songrate of their floater replacements was similar to that of theoriginal owners. Finally, a male’s song rate was not affectedby how frequently he chased intruders, or by the proximity ornumber of neighbors he had. In short, the only information thatbasal song rate of redwinged blackbirds appears to provide toconspecifics is that the territory is occupied. In simulatedterritory takeover attempts, however, song rate was significantlyhigher than the basal rate. Thus, more may be revealed by thesinger in these situations. [Behav Ecol 1991;2:123-132]     

Effects of Exogenous Androgen and Antiandrogen on Territorial and Nonterritorial Red-winged Blackbirds (Aves: Icterinae)

We investigated the role of testosterone (T) in territory establishment and maintenance in male red-winged blackbirds (Agelaius phoeniceus) by implanting exogenous T or pharmacological agents that block the action of T in nonterritorial floaters and territory owners. Floaters with artificially elevated plasma T levels were unable to obtain territories. Territory owners implanted with T did not expand their territories, although they engaged in more aggressive behavior than did control males. Flutamide, which binds to T receptors in target areas, had no effect on territoriality. However, most territory owners given a combination of flutamide and ATD, an aromatization blocker, lost portions of their territories even though they actively defended them. Our results 1) suggest that, although T influences aggressive behavior, elevated plasma levels alone are insufficient to overcome previously-established social relationships between territory owners or between owners and floaters; 2) indicate that impairing the action of T leads to reduced abilities of territory owners to maintain territories against vigorous challenges: and 3) support recent findings that T acts on reproductive behavior in birds through both androgenic and estrogenic metabolites.     

Calling as an ownership convention on pied wagtail territories

Winter feeding territories were more profitable to owners than intruders. Even when intruders landed on a territory undetected they failed to achieve a profitable feeding rate because they fed in areas recently depleted by the owner. For intruders therefore, ownership was a sign of unprofitability. Intruder scalled ‘chis-ick’, apparently to find out if a territory was occupied. Owners replied ‘chee-wee’ and this was usually sufficient to cause the intruder to retreat. Only owners called ‘chee-wee’. Owners reacted more aggressively to tape-recorded broadcasts of the ‘chee-wee’ call played on their territory than to broadcasts of ‘chis-ick’.     

Territorial responses to energy manipulations in the Anna hummingbird

Summary Territorial activity in the Anna hummingbird (Calypte anna) was measured while energy availability on the territory was varied. On days when energy availability was unlimited, residents defended highly exclusive territories primarily by energetically expensive defense behaviors. As energy availability decreased, exclusiveness declined gradually, relative use of energetically inexpensive defense increased, and owners spent less time on the territory.Territorial behavior also varied with short term depressions in energy availability: A lower percentage of intruders was chased and departures of an owner from its territory were more frequent shortly after feeding.When resource dispersion was increased without changing substantially total rewards per territory, chasing by owners increased.     

What factors contribute to an ownership advantage?

In most taxa, owners win fights when defending a territory against intruders. We calculated effect sizes for four factors that potentially contribute to an 'owner advantage'. We studied male fiddler crabs Uca mjoebergi, where owners won 92% of natural fights. Owners were not more successful because they were inherently better fighters (r=0.02). There was a small effect (r=0.18) of the owner's knowledge of territory quality (food availability) and a medium effect (r=0.29) of his having established relations with neighbours (duration of active tenure), but neither was statistically significant. There was, however, a significant effect due to the mechanical advantage the owner gained through access to the burrow during fights (r=0.48, p<0.005).     

Previous agonistic experience determines both foraging behavior and territoriality in the limpet Lottia gigantea (Sowerby)

Lottia gigantea, the owl limpet, is an algal gardener. Territorial individuals actively defend gardens, which consist of clearedareas in the intertidal zone upon which a thick algal filmdevelops and upon which the territory holder feeds. Smaller,nonterritory holders raid these gardens and graze the algalfilm. Territorial individuals must obtain an adequate ration without compromising the productivity of the garden. In contrast,a nonterritory holder grazing on another limpet's territorymust obtain an adequate ration before it contacts the territoryholder and is driven off. In the laboratory, replicate setsof 10 limpets were trained to behave territorially and nonterritorially.Training mimicked natural encounters between territorial andnonterritorial L. gigantea. Limpets given territorial trainingleft significantly (t = -4.92, df = 9, p =.00041) more algalcover behind when grazing (on average 71%) than did limpetstrained to be nonterritorial (on average 50%). Territorial limpets seldom grazed over the same area more than once (4% of the grazedarea). In contrast, nonterritorial limpets frequently foragedover an area more than once; of the area grazed, 20% had beenvisited more than once. Previous agonistic experience determinesboth territorial behavior and foraging strategies, two of thecritical behaviors necessary for successful gardening behavior.Nonterritorial limpets maximize consumption per unit area, whereas territorial limpets appear to forage prudently, leaving a significantly greater proportion of the plant biomass behind.     

Power to Hold Sheltering Burrows by Juveniles of the Signal Crayfish,Pasifastacus leniusculus

Juveniles of the signal crayfish reside during daylight hours in shelters. At twilight they leave for food, at daybreak they either return or find another shelter. We examined conflicts over burrow ownership. At low densities with equal numbers of shelters and crayfish 1/5 of the burrows were occupied. Increasing both the number of crayfish and shelters improved the occupancy close to 50%. Doubling the number of crayfish in relation to the number of shelters increased the occupancy up to 75%. In an experiment with 30 randomly selected crayfish and 15 sheltering holes available the burrow holders were about 1–2 mm longer in carapace length than those found freely moving in the aquarium. Shelter owners were rarely newly moulted individuals. Size asymmetry (2 mm difference in carapace length) between owner and intruder affected the outcome of the contest over burrow ownership. When intruders were larger than owners, takeovers occurred in about 80% of the cases tested. If the owner was large and the intruder small the takeover frequency was about 20%. When the owner and the intruder were of matching size takeovers were still observed in about 45% of the cases. The outcome of the ownership contest has a true meaning. In a nursery-pond experiment, where low-protein food was randomly scattered all around, no size differences were found in carapace lengths of crayfish juveniles residing in different shelters. However, when high-protein food was introduced in a single spot, owners of burrows were significantly larger and more numerous in the nearby shelters than in the shelters furthest away from the food source. Therefore, when food is unevenly distributed the burrow ownership contests may potentially lead to size asymmetries between individuals. This may lead to large individuals nearby the food growing faster than small individuals further away from the food source, a process likely to further enhance size differences.     

To be or not to be? Mating success and survival trade‐offs when switching between alternative reproductive tactics

Hormones underlie the decision of assuming a territorial or a nonterritorial role, with territorial individuals usually having higher hormonal levels than nonterritorial individuals. As a territorial status is linked to higher mating opportunities, it is unclear why animals do not keep high hormonal levels and one explanation is that this would imply survival costs. We have tested this using males of the territorial damselfly Argia emma in the field. We increased juvenile hormone (JH) levels using methoprene in both territorial and nonterritorial males and predicted that: (i) males will keep (the case of territorial males) or become (the case of nonterritorial males) territorial after hormonal increase, and (ii) there will be an increase in mating success for nonterritorial males only and an impaired survival for both male tactics. Hormonally treated males remained or became territorial but had their survival impaired compared with control groups. Also, hormonally treated, ex‐nonterritorial males increased their mating success compared with the other control, nonterritorial males. The reduced survival can be explained proximally by the energy devoted either to the enhanced aggression showed during territory defence or immune function (as detected previously in damselflies). Although nonterritorial males may increase their mating success by switching to a territorial tactic, they are possibly unable to do it naturally as JH is dietary dependent and usually nonterritorial animals are in poorer condition than territorial animals.     

Mate choice or harassment avoidance? A question of female control at the lek

Recent studies on the reproductive behavior of fallow deer,Dama dama, propose that harassment from nonterritorial maleshas a major influence on female movements and mate selection,leading ultimately to the evolution of lek mating in this species.In order to support this statement, one must demonstrate thatfemale movements between lek and isolated territories, and amonglek males, lead to a reduction in levels of harassment. We arguethat current evidence in favor of this view is inconclusive.A quantification of the total harassment costs experienced byfemales in lek and isolated territories has never been made.In addition, female movements within the lek may actually leadto higher levels of disruption and harassment: The rate at whichfemales join male territories increases with harem size (thenumber of females present in the territory), even though haremsare disrupted increasingly with size due to a higher frequencyof intrusions by nonterritorial males. Females also join maleterritories at a higher rate while these males are engaged incopulatory sequences, but copulatory sequences are again associatedwith high levels of disruption and harem instability. In theabove studies it is argued that females are nonselective intheir mating preferences. This assessment is based on the findingthat males that adopt different reproductive strategies do notdiffer in their mating rates. Here mating rate is measured asthe number of copulations received per female-hour. There area number of reasons, however, why females exhibiting matingpreferences might remain longer with preferred males, and sothe above preference measure cannot be used to exclude the possibilitythat females are selective. More research is required to identifythe major factors influencing patterns of mate selection andthe evolution of leks in this species. We suggest a number offield tests that may help to identify these factors.     

Prospectors combine social and environmental information to improve habitat selection and breeding success in the subsequent year

1.?Because habitats have profound effects on individual fitness, there is strong selection for improving the choice of breeding habitat. One possible mechanism is for individuals to use public information when prospecting future breeding sites; however, to our knowledge, no study has shown prospecting behaviour to be directly linked to subsequent choice of breeding site and future reproductive success. 2.?We collected long-term data on territory-specific prospecting behaviour and subsequent breeding in the short-lived northern wheatear (Oenanthe oenanthe). Non-breeders established prospecting territories (<2 ha) that overlapped the breeding territories of conspecifics. We tested whether: (i) prospectors used social and environmental cues that predicted territory-specific breeding success in the following year, and (ii) the prospecting territory was tightly linked to the subsequent breeding territory of the prospector, and whether this link would be weakened by intraspecific competition with original territory owners if they also survived. 3.?As expected, prospectors were attracted to a combination of site-specific cues that predicted future breeding success, i.e. short ground vegetation, a successfully breeding focal pair and successful close neighbours. 4.?Prospecting behaviour was directly linked to the choice of the following year's breeding territory: 79% of surviving prospectors established a breeding territory at their prospecting site in the following year, with their breeding success being higher than other individuals of the same age. As predicted, fidelity to the prospected site was strongly dependent on whether the original territory owner of the same sex had died or moved. 5.?Our findings suggest that the use of multiple cues reduces the negative impact of stochasticity on the reliability of social cues at small spatial scales (e.g. territories) and hence increases the probability of breeding success in the next year. Also, the use of conspecific attraction (i.e. the preference for breeding aggregations) is selectively advantageous because individuals are more likely to find a vacancy in an aggregation as compared to a solitary site. By extension, we hypothesize that species life-history traits may influence the spatial scale of prospecting behaviour and habitat selection strategies.     

Three-player social parasitism games: implications for resource defense and group formation

Abstract: Individuals that produce resources are often exploited by several individuals; such exploitation may or may not be tolerated. We modeled the decision of a resource owner to accept one scrounger (the "satellite") and of both of these to accept being joined by another (the "floater"). In general, satellites tolerated floaters when competition between them was low, while owners tolerated satellites when facilitation between satellite and floater was high. When floaters were likely to find resources without joining, owners were more likely to resist satellites. In some cases, Nash equilibria were also mutually beneficial for two of the three individuals. Our model makes the counterintuitive prediction that mutually beneficial coalitions between satellites and floaters can only arise when the net benefits arising from the other's presence are low. When facilitation between satellites and floaters is high, satellites and owners may form mutually beneficial groups and groups with division of labor, or alternatively, owners may benefit from encouraging floaters to join. Finally, our model suggests there must be differences in competitive ability or some benefit of familiarity for owners to tolerate satellites but not floaters. We discuss empirical evidence for these and other predictions of the model.     

Effects of demographic parameters on metapopulation size and persistence: an analytical stochastic model

An analytical stochastic metapopulation model is developed. It describes how individuals will be distributed among patches as a function of density-dependent birth, death and emigration rates, and the probability of successful dispersal. The model includes demographic stochasticity, but not catastrophes, environmental stochasticity or variation in patch size and suitability. All patches are equally likely to be colonized by migrants. The model predicts: (a) mean and variance of the number of individuals per patch; (b) probability distribution of individuals per patch; (c) mean number of individuals in transit; and (d) turn-over rate and expected persistence time of a single patch. The model shows that (a) dispersal rates must be intermediate in order to ensure metapopulation persistence; (b) the mean number of individuals per patch is often well below the carrying capacity; (c) long transit times and/or high mortality during dispersal reduce the mean number of individuals per patch; (d) density-dependent emigration responses will usually increase metapopulation size and persistence compared with density-independent dispersal; (e) an increase in the per capita net growth rate can both increase and decrease metapopulation size and persistence depending on whether dispersal rates are high or low; (f) density-independent birth, death, and emigration rates lead to a spatial pattern described by the negative binomial distribution.     

Exploring the Grief Experience Among Callers to a Pet Loss Support Hotline

The present study explored the grief experience among callers to the Ontario Veterinary College Pet Loss Support Hotline (PLSH). Summary notes (n = 75) of the conversations between callers and PLSH volunteers were qualitatively analyzed using content analysis. Major content categories emerging from the analysis include personal pet narrative; perceived support sources; grief experiences; relationship with pet; memorialization; grief coping strategies; grief triggers; decision to euthanize; and veterinary interaction. Findings support that pet loss grief is a broad, complex construct, which can be complicated by a pet owner’s perceptions that they have minimal social support sources and negative veterinary interactions. Pet owners involved in the current study appeared comfortable sharing personal stories about their pet’s death when asked. In addition, memorialization appeared to be widely used by PLSH callers and may have helped them cope with their loss. Importantly, the interaction with veterinary staff was identified to potentially aggravate or alleviate a pet owner’s grief experience. Implications for mental health counselors and veterinary staff are that asking pet owners to tell their pet’s story and explore their support network may have value following the loss of a pet. Also, effectively communicating about memorialization and grief coping strategies may be beneficial when talking to owners experiencing grief. Finally, there continues to be a need for curricula and continuing professional training courses for veterinarians and mental health counselors to address topics such as the human–animal bond, grief, euthanasia, and memorialization practices.     

Space‐use strategies of wintering Ovenbirds in Belize: causes and consequences

For long‐distance migrants, territoriality and prey biomass during the non‐breeding season have been linked to body condition that can carry over to affect spring migration and breeding events. For Ovenbirds (Seiurus aurocapilla), studies in Jamaica showed that body condition in mid‐season depended on leaf litter prey biomass and declined seasonally as conditions became drier, and that individuals with sedentary (territorial) and wandering space‐use strategies did not differ in age or body condition. During October and November 2010–2011, we radio‐tracked Ovenbirds in Belize to determine if space‐use patterns differed with age and sex, if space‐use strategy influenced foraging behavior or body condition, and if areas used by wanderers and territory owners differed in food abundance or habitat characteristics. Most Ovenbirds (41 of 51, 80.4%) possessed small (1‐ha) territories with largely non‐overlapping cores, but 22.5% (10 of 51) of birds were wanderers (～7‐ha home range). Early season space use was predicted by age class, with most wanderers (90%, 9 of 10) being first‐year birds and most territory owners (63%) being older birds. Sex ratios of wanderers and territory owners did not differ. We found that wanderers may have been at a disadvantage because they had significantly lower foraging rates and lower relative body masses than territorial birds, although baseline corticosterone levels did not differ. Habitat characteristics of areas used by wanderers and territory owners did not differ nor did biomass of ground‐surface arthropods, likely because ranges of most wanderers overlapped those of territory owners. Using stable hydrogen isotopes in feathers, we found that first‐year Ovenbirds that were wanderers tended to have a more northern natal origins than sedentary birds, though the difference was not significant. Longer migration distances could delay arrival and reduce competitive ability. Our results suggest that wandering may not be an alternative and equally successful strategy, at least early in the season, and instead young birds may be competitively excluded from territory ownership.     

Effects of population growth on Crested Tit Parus cristatus post-fledging settlement

From 1987 to 1993, the winter density of Crested Tits Parus cristatus in north Belgium increased 2.76 times. The increase was the result of high annual survival rates of both adult and first-year birds despite a low reproductive success (number of fledglings per female) due to high predation of nestlings. A fc-factor analysis assuming intermediate costs of post-fledging dispersal and settlement gave the best fit. First-year birds had two options when trying to settle in a prospective breeding territory: (1) establish a new territory during August or early September and defend it against neighbouring flocks during winter or immigrants in early spring or both, or (2) overwinter as a subordinate in a mixed-age flock and pair with a widowed adult or replace a territory owner in early spring ("hopeful dominant stategy"). Settlement strategies varied with density; at low density, only the hopeful dominant strategy was observed, whereas at higher density, both strategies occurred.     

Territory acquisition during winter by juvenile Willow Tits Parus montanus

Willow Tits Parus montanus live within exclusive territories in non-kin winter flocks with a dominance hierarchy in which males dominate females and adults dominate juveniles. Because they live in habitats that are saturated with dominant territory owners, the options of subordinate juveniles surviving the winter are: (1) to become a dominant owner of a vacated territory, (2) to stay in an occupied territory and hope for ownership or (3) to leave the area and hope for territory acquisition elsewhere. Removal experiments during December to February revealed that particularly the most dominant of the juvenile pairs left their own flock territory and replaced birds experimentally removed from a neighbouring flock, if by doing so they increased their own dominance position. It is suggested that juvenile Willow Tits updated their information about the composition and dominance structure of adjacent winter flocks by regularly visiting these territories and attempted to become dominant owners during winter, thereby increasing their chances of breeding.     

Incorporating territory compression into population models

The ideal despotic distribution, whereby the lifetime reproductive success a territory's owner achieves is unaffected by population density, is a mainstay of behaviour-based population models. We show that the population dynamics of an island population of Seychelles warblers ( Acrocephalus sechellensis ) cannot be modelled with an ideal despotic distribution, and suggest the effects of both territory shrinkage and territorial disputes on reproductive success must be included to adequately model the population dynamics of this species. To do this we introduce two different approaches. The first is reductionist, using data on how population density affects individuals' reproductive success to predict population growth rates. Because such a model is mechanistic, it can be used to predict population dynamics in novel environments, making it a desirable long-term solution. However, because territorial populations are typically tightly regulated, birth and death rate data at low population densities are often unavailable. Hence, our second approach statistically infers the relationship between population density and per territory reproductive success, and thus provides a stop-gap solution for the shorter term. Our analysis indicates that although the Cousin population of Seychelles warblers is highly resilient to environmental stochasticity, the degree of resilience is considerably underestimated by approaches that ignore intrinsic regulation through territory shrinkage and territorial disputes.     

Multiple asymmetry and concord resolutions of a conflict

A model for a population-game with multiple asymmetry is studied, in which the participants are assumed to be different from one another both in size and in status as owners or non-owners of a territory. Only owners can reproduce, hence natural selection is assumed to operate in favor of the increase of ownership-time. Conditions for the evolutionary stability of the Bourgeois Principle of owner-priority, despite difference in body size, are characterized. It is shown that ownership-priority tends to be at least partially replaced by strength-priority as the availability of habitats, the expected longevity of potential intruders and the harm inflicted on the loser of an aggressive confrontation decrease, and as the expected longevity of the owner increases. It is further established that the combined effect of all these parameters can be characterized by a single parameter, referred to as the concord coefficient of the population. Finally, when this parameter reaches a certain critical level, only strength-priority can prevail. If the concord coefficient decreases below this critical level, no priority-rule can remain stable in the population, in which case aggressive confrontations cannot be avoided, at least in certain situations. In this case, it is shown that aggression emerges first among low-rank individuals.     

Reproductive parasitism: male and female responses to conspecific and heterospecific intrusions at spawning in a mouth‐brooding cichlid Ophthalmotilapia ventralis

A rare form of alternative reproductive behaviour without simultaneous parasitic spawning was observed in Ophthalmotilapia ventralis, a lekking mouth‐brooding cichlid from Lake Tanganyika. Floater males attempted to sneak opportunistically into the territory to actively court the female, while the owner (bourgeois male) defended the territory against other potential intruders. Floater males had more body fat than territory owners and generally higher condition factors. In field experiments, the response of bourgeois males and courted females was tested towards floaters and egg predators (a catfish Synodontis multipunctatus) present in the territories. Territory owners responded aggressively particularly to floaters, and female responsiveness to bourgeois male courtship tended to decline when floaters were present. The potential influence of reproductive parasitism on sexual selection in mouth‐brooding cichlids is discussed.