Differences In Territory Quality Research Articles

Females are more determinant than males in reproductive performance in the house sparrow Passer domesticus

Which sex has a more determinant role in reproductive performance? This is a long standing question in evolutionary ecology. Theory predicts and several pieces of evidence have indicated that females are more determinant than males. However, a direct test of this hypothesis has never been made. Here we perform such a direct test by using an alternative analytical approach, controlling for age and/or individual experience, and a captive population of the house sparrow Passer domesticus, a monogamous bi‐parental dimorphic species in which both sexes contribute with approximately equal amounts of parental care. In this species, it has been demonstrated that contribution by males to offspring parental care is crucial to maximize reproductive success. Captive conditions with absence of predators and availability of food ad libitum allow us to control several important factors that may affect reproductive performance, such as environmental fluctuations in resource availability and differences in territory quality, without affecting reproductive performance. We consider four types of pairs, and our main prediction derived from the hypothesis is that mixed pairs involving an experienced female (FBM × EF) should present better reproductive performance than mixed pairs involving a first‐time breeder female (EM × FBF). Our results confirm the general pattern reported in other bird species that older or more experienced individuals enjoy a higher reproductive success than first‐time breeders. In addition, in agreement with our main prediction, we found that FBM × EF produced significantly more fledglings and had higher fledging success than EM × FBF. Our results, for the first time demonstrate the broadly accepted statement that females have a more determinant role than males in reproductive performance.

Temporal vs. spatial variation in stress-associated metabolites within a population of climate-sensitive small mammals.

ABSTRACTTemporal variation in stress might signify changes in an animal’s internal or external environment, while spatial variation in stress might signify variation in the quality of the habitats that individual animals experience. Habitat-induced variations in stress might be easiest to detect in highly territorial animals, and especially in species that do not take advantage of common strategies for modulating habitat-induced stress, such as migration (escape in space) or hibernation (escape in time). Spatial and temporal variation in response to potential stressors has received little study in wild animals, especially at scales appropriate for relating stress to specific habitat characteristics. Here, we use the American pika (Ochotona princeps), a territorial small mammal, to investigate stress response within and among territories. For individually territorial animals such as pikas, differences in habitat quality should lead to differences in stress exhibited by territory owners. We indexed stress using stress-associated hormone metabolites in feces collected non-invasively from pika territories every 2 weeks from June to September 2018. We hypothesized that differences in territory quality would lead to spatial differences in mean stress and that seasonal variation in physiology or the physical environment would lead to synchronous variation across territories through time. We used linear mixed-effects models to explore spatiotemporal variation in stress using fixed effects of day-of-year and broad habitat characteristics (elevation, aspect, site), as well as local variation in habitat characteristics hypothesized to affect territory quality for this saxicolous species (talus depth, clast size, available forage types). We found that temporal variation within territories was greater than spatial variation among territories, suggesting that shared seasonal stressors are more influential than differences in individual habitat quality. This approach could be used in other wildlife studies to refine our understanding of habitat quality and its effect on individual stress levels as a driver of population decline.

Simultaneous polygyny by a male Black-capped Vireo (Vireo atricapilla) in central Texas

ABSTRACT Although polygyny is common and regular among a small proportion of North American songbirds, some socially monogamous passerines may also exhibit occasional polygyny. We present evidence for only the second documented case of polygyny within the Vireonidae and the first documentation for polygyny in the endangered songbird the Black-capped Vireo (Vireo atricapilla). We located two simultaneous nests being tended by the same color-banded male vireo in a territory adjacent to an unpaired male. We suspect that differences in territory quality, rather than male quality, unbalanced sex ratios, or asynchronous settlement, were drivers of polygyny in this example.

Assessment and decision-making in a Caribbean damselfish: nest-site quality influences prioritization of courtship and brood defence

In systems where territory quality varies, animals are expected to exhibit plasticity in behaviour in order to maximize fitness relative to their present territory quality. This requires assessment of territory quality followed by decision-making in relation to the priority of activities necessary for survival and reproduction. We examined how differences in territory quality of beaugregory damselfish (Stegastes leucostictus) influence the prioritization of courtship and egg defence by comparing behavioural responses of males defending artificial sites (high quality) with males defending natural sites (low quality) when presented with an egg predator, a conspecific female, and a simultaneous choice between both. A significant three-way interaction of territory quality, presentation type and stimulus was observed for time near stimuli. In paired presentations, males defending low-quality territories spent more time near a female and less near an egg predator; while males on high-quality territories spent more time near a predator than a female. Additionally, comparing single and paired presentations reveals that behaviours towards egg predators remain constant while behaviours towards females decrease with paired stimuli. These data suggest that territory quality and ecological context impact decision-making and the relative values of potential reproduction and/or past reproductive effort.

Male breeding success is predicted by call frequency in a territorial species, the agile frog (Rana dalmatina)

Calling behaviour and the characteristics of the male call are important for both female mate choice and male mating success in anurans. As with most other ranid frogs, males of the agile frog ( Rana dalmatina Fitzinger in Bonaparte, 1839) emit advertisement calls during the mating period. However, since males occupy and defend territories, it is not clear whether the calls serve to defend a territory and (or) to attract a mate. We investigated the relationship between male call characteristics and male breeding success in a field study by relating individual males’ call parameters (viz. call duration, number pulses, pulse rate, and fundamental frequency) with their breeding success as indicated by the number and size of egg clutches in the territories of males. We found that the number and size (in number of eggs) of clutches in the territories of males increased with decreasing fundamental frequency of calls. We found no correlation between territory characteristics and breeding success, suggesting that the observed correlation between male call characteristics and mating success is not likely to be explained by differences in territory quality, but by female potential preference for males calling with low fundamental frequency.

Territory quality affects female preference in a Lake Victoria cichlid fish

Mate preferences on male colour have been implicated in generating and maintaining species diversity among haplochromine cichlid fish. Their lek-like mating system suggests that not only male colour but also territory quality is instrumental in mate choice. We assessed the relative importance of territory quality and male colour in mate choice by testing whether territory quality can override the female preference for males of her own colour in the Lake Victoria cichlid genus Pundamilia. First, we showed in experimental groups that the dominant male preferentially monopolised a large tube relative to a small tube. The situation mimics quality difference in rocky crevices that serves as a focal point for male courtship display. Second, in mate-choice tests, Pundamilia nyererei females were allowed to choose between closely related P. nyererei and P. pundamilia males; these species differ strikingly in male nuptial coloration, but little else. We gave either both males the same small tube or one of them a large tube. The preference of P. nyererei females for P. nyererei males in the control situation (where both males had a small tube) was significantly diminished in favour of P. pundamilia males when the latter had the large tube. The results provide experimental evidence that differences in territory quality can override the female preference for males of her own colour. This finding is critical for a recent hypothesis proposing that male competition for mating territories can facilitate the process of sympatric speciation by sexual selection.

Delayed Breeding Affects Lifetime Reproductive Success Differently in Male and Female Green Woodhoopoes

In cooperatively breeding species, many individuals only start breeding long after reaching physiological maturity [1], and this delay is expected to reduce lifetime reproductive success (LRS) [1-3]. Although many studies have investigated how nonbreeding helpers might mitigate the assumed cost of delayed breeding (reviewed in [3]), few have directly quantified the cost itself [4, 5] (but see [6, 7]). Moreover, although life-history tradeoffs frequently influence the sexes in profoundly different ways [8, 9], it has been generally assumed that males and females are similarly affected by a delayed start to breeding [7]. Here, we use 24 years of data to investigate the sex-specific cost of delayed breeding in the cooperatively breeding green woodhoopoe (Phoeniculus purpureus) and show that age at first breeding is related to LRS differently in males and females. As is traditionally expected, males that started to breed earlier in life had greater LRS than those that started later. However, females showed the opposite pattern: Those individuals that started to breed later in life actually had greater LRS than those that started earlier. In both sexes, the association between age at first breeding and LRS was driven by differences in breeding-career length, rather than per-season productivity. We hypothesize that the high mortality rate of young female breeders, and thus their short breeding careers, is related to a reduced ability to deal with the high physiological costs of reproduction in this species. These results demonstrate the importance of considering sex-specific reproductive costs when estimating the payoffs of life-history decisions and bring into question the long-held assumption that delayed breeding is necessarily costly.

Determining habitat quality for the cooperatively breeding Rufous Treecreeper, Climacteris rufa

Abstract The theory of habitat selection predicts that organisms should use habitat that maximizes their fitness. The cooperatively breeding Rufous Treecreeper, Climacteris rufa, exhibits non‐random habitat use at a number of spatial scales. By assessing correlative relationships between nest‐site use and nest success, and territory use and reproductive success and survival, it was determined whether non‐random use of habitat yields fitness benefits. It was also determined whether breeding group size contributed significantly to fitness once differences in territory quality had been considered. Structural characteristics of nest sites that were positively correlated with the probability of a site being used had no relationship with nest success. This result probably reflects the relatively unrestricted access to an abundance of suitable nest sites in the study area. Habitat traits that predicted territory use by treecreepers were positively correlated with a number of fitness measures. They were also positively correlated with breeding group size and provisioning rate to nestlings, which in turn were correlated with fitness. However, group size was not significantly related to any measure of fitness, except primary male survival, once territory quality had been considered. The quality of territories occupied by Rufous Treecreepers appeared to be a significant factor for breeding group fitness.

Polygyny in the dusky warbler, Phylloscopus fuscatus: the importance of female qualities

The polygyny threshold model states that secondary females gain benefits from high territory quality that outweigh the costs of sharing a male. We aimed to test this prediction using the dusky warbler as a model species. We first showed that neither the shifted sex ratio hypothesis nor the no-cost models were likely to apply to our study. Secondary females settled in territories of higher quality (high food abundance, low predator density) and had a nonsignificantly higher reproductive success than simultaneously settling monogamous females. However, there were strong indications that these two groups of females differed intrinsically. Secondary females were older than late monogamous females, and while they replaced lost clutches more often, they also suffered from a nonsignificantly higher winter mortality. Consequently, it was impossible to tell whether differences in reproductive success were caused by differences in territory quality or in female qualities. Our study suggests that female choice may also depend on characteristics that are specific to the individual, and may therefore be more sophisticated than allowed for in traditional polygyny models. In other words, the polygyny threshold may be not the same for all individuals. We suggest that prior breeding experience may help older females to profit more from the benefits and to suffer less from the costs of polygyny than young females.

Nestling sex ratio variation in the cooperatively breeding acorn woodpecker ( Melanerpes formicivorus )

We examined sex ratio variation in the cooperatively breeding acorn woodpecker (Melanerpes formicivorus) over a 27-year period in central coastal California. The sex ratio of eggs is even or possibly biased toward females. However, hatching asynchrony and brood reduction differentially favor the slightly larger males such that the sex ratio when young become self-sufficient is 54.0% males, slightly but significantly different from 50:50. This bias, or at least the differential mortality that produces it, does not appear to be explainable by any of the major hypotheses for an overall sex bias. These include the repayment model, local resource competition, and sexual size dimorphism, all of which predict a female bias or a male bias significantly smaller than that observed. On an individual level, we found no evidence for facultative sex ratio manipulation related to annual differences in the acorn crop, apparent seasonal declines in food availability, or differences in territory quality. We also found no evidence for a non-binomial distribution of sexes within broods despite the potential fitness benefits of creating large coalitions of same-sexed siblings. Males inherit their natal territories more frequently than do females, and we speculate that birds may invest more in sons either to increase the probability that they will be able to pass along their territory to their descendants or to facilitate their sons' ability to compete as future cobreeders. Alternatively, acorn woodpeckers may be unable to fully compensate for the ancillary bias caused by differential juvenile survivorship, leading to unequal investment in the sexes contrary to the prediction of Fisher. Opposite to what has been found in other birds and mammals, the faster growth and larger size of male nestlings appears to confer a survival benefit rather than a cost.

Male-male competition and parental care in collared flycatchers (Ficedula albicollis): an experiment controlling for differences in territory quality.

Females are known to benefit from mate choice in several different ways but the relationship between these benefits has received little attention. The quality of resources provided by males, such as nest sites, and paternal care are often assumed to covary positively However, because the location of the nest affects the cost of parental care, these two benefits from mate choice can easily be confounded. To investigate the provisioning ability of successful competitors while controlling for differences in territory quality we removed early-settled pairs of collared flycatchers (Ficedula albicollis) and allowed replacement by later-arriving males or floaters (i.e.'poor competitors'). A control group of early-settled males (i.e. 'good competitors') had their females removed. Females paired to good competitors enjoyed a significantly higher reproductive success and tended to receive more parental assistance from their mates compared with females mated to poor competitors. Thus, some males seem able not only to compete successfully over resources but also to feed their offspring at a relatively higher rate. An alternative explanation, that poor competitors invested less in offspring quality in response to a lower share of paternity, could be rejected. The rate of extra-pair paternity did not differ between the two treatment groups. Our results suggest that male- male competition can sometimes facilitate female choice of superior care-givers. Thus, a female's benefit from choosing a competitive male may not be restricted to the quality of the resource he defends but can also include superior paternal care.

Reproductive success increases with degree of kinship in cooperative coalitions of female red howler monkeys ( Alouatta seniculus )

Evaluation of evolutionary mechanisms proposed to promote cooperative behavior depends on the relative influence of the behavior on the reproductive success of individuals, the reproductive success of the group in which they interact behaviorally, and the degree of gene correlation among cooperators. The genetic relationship within cooperative coalitions of female red howler monkeys was examined for three populations with different densities and growth rates. Patterns of gene correlation change within coalitions is documented using data from the mitochondrial and nuclear genomes, and long-term census monitoring. Differences in fecundity and infant survivorship within and between groups of unrelated (r¯=0) and related (r¯≥ 0.25) females are compared. Females that emigrate from their natal groups form coalitions with other migrant females. These coalitions attempt to establish a territory and, once successful in producing offspring, exclude other females from feeding resources. Females in these coalitions had different mtDNA haplotypes and a genetically estimated mean r of 0, supporting demographic data on emigration patterns indicating that these females rarely have the opportunity to form coalitions with kin. Patterns of recruitment and rate of matriline development within social groups supported behavioral data indicating that females actively attempt to promote their own matriline as breeders over that of other females, and that some matrilines are more successful at this than others. Mean r among females was significantly higher in coalitions established as social groups for several generations (r¯=0.44). In these groups, females all shared the same mtDNA haplotype, and mtDNA haplotype divergence was significantly higher between than within groups. Females in coalitions with kin had significantly higher reproductive success than females in unrelated coalitions in all populations. This difference was not a function of coalition size, number of males, socionomic sex ratio, or primiparity, although anecdotal evidence suggests that allomothering may compensate for inept new mothers in related coalitions more often than in unrelated ones. Differences in territory quality could not be ruled out as a potential causal factor in the saturated populations, but were unlikely in the low-density, growing population. There were substantial differences among long-established coalitions in overall reproductive output in all three populations, and this was significantly correlated with the number of breeding females. Increase in coalition size was a function of both group age and the behavioral tolerance among females. Regardless of the underlying reasons for the patterns observed, reproductive success clearly increases with degree of gene correlation among females within cooperative coalitions, and coalitions that recruit more daughters produce more offspring. The nature of the cooperative relationship among group females directly influences both of these outcomes. This is associated with substantial genetic differentiation among social groups within populations, creating conditions in which genetic tendencies towards cooperative behavior can become tightly associated with group reproductive success.

Delayed Breeding in Avian Social Systems: the Role of Territory Quality and "Floater" Tactics

Abstract In many avian societies, young birds delay breeding beyond the age of sexual maturity. Most previous hypotheses of delayed breeding have emphasized forces that keep young birds from becoming breeders. We develop a model of delayed breeding which includes the future acquisition of a high quality territory as a potential direct benefit of delayed breeding. Strong differences in territory quality, age-correlated asymmetries in resource holding potential, and territory site tenacity set the stage for young birds to either breed immediately on a poor territory, or obtain a high quality territory through reproductive delay on or near the site. A wide variety of species and social organizations reveal common patterns of breeding status acquisition through behaviours as nonbreeders with site tenacity on or immediately near the breeding site. A review of 'floater' strategies reveals that nonbreeders frequently have restricted home ranges that encompass one or more breeding territories, and prior experience at a site improves their chances of acquiring a territory in future years. This pattern of territory acquisition argues for incorporating direct benefits into models of delayed breeding. We discuss the potential applications to understanding delayed breeding in social systems as apparently different as cooperatively-breeding birds, migratory passerines, colonial breeding gulls, and lek-breeding grouse and manakins.

Clutch Size Determination in the Marsh Tit (Parus Palustris)

By providing supplemental food to Marsh Tits (Parus palustris) from the day the first egg was laid, effects on clutch size could be directly attributed to food without the confounding effects on laying date. Females provisioned with additional food responded by laying, on average, on egg more than control females. Differences in territory quality did not influence this result because, on territories occupied in both years, one more egg was laid in the year of provisioning. Although the rate and amount of extra food provided were equal during the two experimental years, the resulting clutch sizes of provisioned females differed between years by more than one egg in absolute terms. Further, the mean clutch size of provisioned females declined seasonally in parallel to that of unprovisioned females. I conclude that clutch size in Marsh Tits is determined by a tactical decision based on declining values of offspring with the progress of the season. However, within the limits sets by this tactical decision, the availability of food during egg—laying also plays a role.

Cooperative Enhancement Of Reproductive Success in Tropical Wren Societies

Stripe—backed Wrens, Campylorhynchus nuchalis, live in cooperative groups of up to 14 adults in which all members share in defense of the common territory, in construction and defense of roosting and breeding nests, and in the care of young produced by a single breeding pair. A 5—yr study of a completely marked population of 25—30 groups in the Venezuelan savanna shows that breeders (principals) assisted by two or more nonreproductive auxiliaries have much greater reproductive success than those with less help. Per capita production of independent juveniles in higher, as well. Only groups with at least two auxiliaries successfully rear two clutches in a season. The proportion of nesting attempts successful in producing fledglings is much higher for groups of four adults or more than for smaller groups, probably because of lesser predation on the nests of large groups. The success of large groups is not likely due to differences in territory quality of breeder experience. Rates of food delivery to nestlings and number of fledglings per successful nest are as high for pairs and trios as for larger groups. However, feeding of nestlings and fledglings by auxiliaries frees the principals from these tasks and probably makes multiple successful clutches possible. Auxiliaries directly defend the breeding nest from predators and competitors, although the principle male is most active in defense. Feeding efforts of auxiliaries are probably linked to increased nesting success primarily through enabling the principal male to defend the nest better. Aid—giving by auxiliaries is explained (1) by its effectiveness in improving the reproductive success of close kin through reducing risk of predation for nestlings, (2) by the probability of reciprocation of such effective help, and (3) by the low productivity of breeding outside a large established group. Data from this population of wrens constitute some of the strongest evidence to data that group defense against predators can provide the impetus for cooperative breeding.