Territorial occupancy and breeding performance in a migratory raptor do not follow ideal despotic distribution patterns

It has commonly been argued that many territorial species select their breeding sites following an ideal despotic distribution model, in which the most productive, high-quality territories are more frequently occupied. Theoretical and empirical studies have shown that this occupancy pattern may have population regulatory consequences, leading to density dependence in heterogeneous habitats. During a 9-year research project in a forested area of south-eastern Spain, we tested some of the predictions of the ideal despotic distribution model and the site-dependent population regulation theory in a migratory raptor species, the booted eagle Hieraaetus pennatus . Contrary to the predictions of the despotic model, our results showed that the temporal pattern of territorial occupation did not differ from randomness, and that the territory occupancy rate was not significantly related to the reproductive parameters considered. At population level, the breeding variables were density independent, suggesting the absence of site-dependent regulation. In addition, we were unable to find significant differences in the habitat characteristics between high-quality and low-quality territories, classified according to the criteria of both occupancy frequency and average productivity. Overall, our results suggest that booted eagles select their territories at random, probably due to the lack of strong environmental heterogeneity, and that occupancy rate is not a good measure of territory quality for the population studied.     

Seasonal effects of density on territory occupation by males of the satyrine butterfly Paryphthimoides phronius (Butler 1867)

Territorial defense in butterflies may be related to both population density and climatic conditions. If these factors change throughout the year, males are expected to adaptively adjust their behavior in order to maximize reproductive success. In this study, we analyzed the annual dynamics of territory occupation by males of the satyrine butterfly Paryphthimoides phronius at a mildly seasonal subtropical site in southeastern Brazil. We investigated the relationship between the number of defended sites, number of males disputing mating areas, proportion of males adopting alternative mate-locating tactics, and the proportion of time invested in territorial disputes with annual variations in temperature and male density. We found little support for the influence of temperature on the dynamics of territory occupation. On the other hand, the number of defended sites increased with male density, whereas the number of males inside each territory, the proportion of satellite males, and the proportion of time spent in territorial disputes were unrelated to variations in population abundance. Territory defense seems to be adopted whenever possible. We conclude that, instead of increasing the number of individuals disputing the same territory during months of high population abundance, males apparently opt to colonize and defend new and, maybe, suboptimal areas.     

Influence of age on reproductive performance in the Seychelles warbler

I studied age-related breeding performance of the cooperativelybreeding Seychelles warbler (Acrocephalus sechellensis) on CousinIsland, Seychelles, during 14 years. The annual number of youngthat fledged is significantly related to territory quality andnumber of helpers in the breeding group. Accounting for thesefactors and for the partner's breeding experience, annual productionof fledglings by breeding birds increases from 2 to 5 yearsand decreases beyond 5 years of age. Age-related changes inreproductive success within breeding individuals, paired withthe same experienced partner and occupying the same breedingterritory with similar amount of food from 2 to 8 years of age,show that Seychelles warblers have higher hatching success andproduce more hatchlings and fledglings as they become older.This is probably not a response to decreasing residual reproductivevalue caused by decreasing life expectancy as they become older.Primiparous warblers produce the same number of fledglings asmultiparous warblers of the same age, have a similar life expectancyas multiparous warblers, and occupy territories with similaramounts of resources available for reproduction. As all warblershave similar access to food before reproduction and similarforaging efficiency, the low reproductive success in youngerwarblers cannot be ascribed to differences in environment butto the bird's ability to breed successfully (e.g., a resultof previous helping and/or breeding experience). Effects ofsenescence on reproduction begin to occur from age 6 for bothsexes. From that age, eggs have lower hatching success, butfledging success remains the same. Birds that start breedingat a young age on a given quality territory produce more fledglingsin their lifetime than birds that delay breeding. Many old birdsnever fledge young of their own. They have not been able tobreed because of a shortage of breeding territory vacancies.[BehavEcol 7: 417–425 (1996)]     

Territory Occupancy and Parental Quality as Proxies for Spatial Prioritization of Conservation Areas

In order to maximize their fitness, individuals aim at choosing territories offering the most appropriate combination of resources. As population size fluctuates in time, the frequency of breeding territory occupancy reflects territory quality. We investigated the relationships between the frequency of territory occupancy (2002–2009) vs. habitat characteristics, prey abundance, reproductive success and parental traits in hoopoes Upupa epops L., with the objective to define proxies for the delineation of conservation priority areas. We predicted that the distribution of phenotypes is despotic and sought for phenotypic characteristics expressing dominance. Our findings support the hypothesis of a despotic distribution. Territory selection was non-random: frequently occupied territories were settled earlier in the season and yielded higher annual reproductive success, but the frequency of territory occupancy could not be related to any habitat characteristics. Males found in frequently occupied territories showed traits expressing dominance (i.e. larger body size and mass, and older age). In contrast, morphological traits of females were not related to the frequency of territory occupancy, suggesting that territory selection and maintenance were essentially a male''s task. Settlement time in spring, reproductive success achieved in a given territory, as well as phenotypic traits and age of male territory holders reflected territory quality, providing good proxies for assessing priority areas for conservation management.     

Sex biased natal dispersal in a closed, saturated population of Seychelles warblers Acrocephalus sechellensis

The distances that individuals disperse, from their natal site to the site of first breeding and between breeding sites, have important consequences for the dynamics and genetic structure of a population. Nearly all previous studies on dispersal have the problem that, because the study area encompassed only a part of the population, emigration may have been confounded with mortality. As a result long-distance dispersers may have been overlooked and dispersal data biased towards short distances. By studying a virtually closed population of Seychelles warblers Acrocephalus sechellensis we obtained almost unbiased results on several aspects of dispersal. As in the majority of other avian species, natal dispersal distance was female biased in the Seychelles warbler. Female offspring also forayed further from the natal territory in search of breeding vacancies than male offspring. The sex bias in natal dispersal distance did, however, depend on local breeding density. In males, dispersal distance decreased as the number of territories bordering the natal territory increased, while in females, dispersal distance did not vary with local density. Dispersal by breeders was rare and, unlike in most species, distances did not differ between the sexes. We argue that our results favour the idea that the sex bias in natal dispersal distance in the Seychelles warbler is due to inbreeding avoidance and not resource competition or intrasexual competition for mates.     

Restricted dispersal reduces the strength of spatial density dependence in a tropical bird population

Spatial processes could play an important role in density-dependent population regulation because the disproportionate use of poor quality habitats as population size increases is widespread in animal populations-the so-called buffer effect. While the buffer effect patterns and their demographic consequences have been described in a number of wild populations, much less is known about how dispersal affects distribution patterns and ultimately density dependence. Here, we investigated the role of dispersal in spatial density dependence using an extraordinarily detailed dataset from a reintroduced Mauritius kestrel (Falco punctatus) population with a territorial (despotic) breeding system. We show that recruitment rates varied significantly between territories, and that territory occupancy was related to its recruitment rate, both of which are consistent with the buffer effect theory. However, we also show that restricted dispersal affects the patterns of territory occupancy with the territories close to release sites being occupied sooner and for longer as the population has grown than the territories further away. As a result of these dispersal patterns, the strength of spatial density dependence is significantly reduced. We conclude that restricted dispersal can modify spatial density dependence in the wild, which has implications for the way population dynamics are likely to be impacted by environmental change.     

Daughters on request: about helpers and egg sexes in the Seychelles warbler

The Seychelles warbler (Acrocephalus sechellensis) was an endangered endemic of the Seychelles islands where, until 1988, the entire population of ca. 320 birds was restricted to the one island of Cousin Island (29 ha). Additional breeding populations were successfully established on the islands of Aride (68 ha, 1988) and Cousine (26 ha, 1990) and now with the existence of ca. 2000 warblers on three islands the conservation status of the warbler has improved from endangered to vulnerable. Emigration from the island is extremely rare, so birds that disappeared were known to have died. Almost every bird on Cousin Island has been individually colour ringed and monitored throughout all breeding attempts during a 17-year period (1985-2002; total ca. 2400 birds). These birds were also blood sampled for molecular parentage and sex analyses. Therefore the lifetime reproductive success of many birds is known. Although warblers can breed independently in their first year, some individuals remain in their natal territory as subordinates, and often help by providing nourishment to non-descendant offspring. The frequency of 'helping' is affected by habitat saturation and variation in territory quality (insect prey availability). The long-term benefits of helping are higher for daughters than for sons, and it is therefore no wonder that most helpers are daughters from previous broods. Furthermore, on low-quality territories breeding pairs raising sons gain higher fitness benefits than by raising daughters, and vice versa on high-quality territories. Female breeders adaptively modify the sex of their single-egg clutches according to territory quality: male eggs on low quality and female eggs on high quality. The Seychelles warbler is a beautiful example of behavioural and life-history adaptations to restricted circumstances.     

The role of group size and environmental factors on survival in a cooperatively breeding tropical passerine

1. Variation in survival, a major determinant of fitness, may be caused by individual or environmental characteristics. Furthermore, interactions between individuals may influence survival through the negative feedback effects of density dependence. Compared to species in temperate regions, we have little knowledge about population processes and variation in fitness in tropical bird species. 2. To investigate whether variation in survival could be explained by population size or climatic variables we used capture-recapture models in conjunction with a long-term data set from an island population of the territorial, cooperatively breeding Seychelles warbler (Acrocephalus sechellensis). The lack of migration out of the study population means that our results are not confounded by dispersal. 3. Annual survival was high, both for adults (84%) and juveniles (61%), and did not differ between the sexes. Although there was significant variation in survival between years, this variation could not be explained by overall population size or weather variables. 4. For territorial species, resource competition will work mainly on a local scale. The size of a territory and number of individuals living in it will therefore be a more appropriate measure of density than overall population density. Consequently, both an index of territory quality per individual (food availability) and local density, measured as group size, were included as individual covariates in our analyses. 5. Local density had a negative effect on survival; birds living in larger groups had lower survival probabilities than those living in small groups. Food availability did not affect survival. 6. Our study shows that, in a territorial species, although density-dependent effects might not be detectable at the population level they can be detected at the individual territory level - the scale at which individuals compete. These results will help to provide a better understanding of the small-scale processes involved in the dynamics of a population in general, but in particular in tropical species living in relatively stable environments.     

Can redistribution of breeding colonies on a landscape mitigate changing predation danger?

The reproductive success of colonially breeding species depends in part upon a trade‐off between the benefit of a dilution effect against nestling predation within larger colonies and colony conspicuousness. However, there may be no net survivorship benefit of dilution if smaller colonies are sufficiently inconspicuous. This raises the question about how the size distribution of breeding colonies on a landscape might change as the predation danger for nestlings changes. In southwest British Columbia, Canada, bald eagle Haliaeetus leucocephalus populations have increased exponentially at ～5% per year in recent decades and prey upon nestlings of colonial breeding great blue herons Ardea herodias faninni. Motivated by field data on reproductive success in relation to colony size, modeling is used to ask under which circumstances trading off a dilution benefit against colony conspicuousness can improve population reproductive success. That is, which colonial nesting distribution, dispersed and cryptic versus clumped and conspicuous, best mitigates predation danger on nestlings? When predators are territorial, the modeling predicts a dispersed nesting strategy as attack rate increases, but not as predator numbers increase. When predators are non‐territorial, the modeling predicts a dispersed nesting strategy as predator numbers and/or attack rates increase. When predators are both territorial and non‐territorial, colonial nesting within a predator's territory improves reproductive success when attack rates are low. This suggests nesting in association with territorial predators may offer decreased levels of predation when compared with nesting amongst non‐territorial predators. Thus a change in the colony size distribution of colonially breeding species might be anticipated on a landscape experiencing a change in predation danger.     

Dynamics of habitat distribution in breeding mallards: assessing the applicability of current habitat selection models

The applicability of ideal free, ideal despotic and ideal preemptive habitat selection models to explain dynamics of habitat distribution of breeding mallards ( Anas platyrhynchos ) was explored. Data from 35 lakes studied between 1985 and 2000 were used to examine overall habitat distribution of breeding pairs, breeding success in different habitats, within-year order of habitat occupation, and density dependence of habitat distribution and breeding success. Two habitat types, rich and poor, were defined based on the structure and luxuriance of shore vegetation; each lake belonged to one or the other of the habitat types. Breeding pairs used the rich habitat more than expected, breeding density also being higher there than in the poor habitat. Both average brood density and breeding success were higher in the rich habitat than in the poor. Breeding success was not density dependent, neither when analysed separately for the habitat types, nor in the study area in general. Within season, arriving mallard pairs did not occupy rich lakes earlier than poor lakes. An isodar analysis based on between-year variation of the breeding density in rich and poor habitats revealed that habitat distribution of breeding pairs was not density dependent. By contrast, density in the rich habitat increased and proportional use of the poor habitat decreased with increasing overall population density, i.e. the rich habitat got increasingly crowded. None of the habitat selection models considered was applicable to explain the dynamics of habitat distribution of breeding mallards.     

Density-dependent habitat selection: Testing the theory with fitness data

Summary According to density-dependent habitat selection theory, reproductive success should decline with increased density. Fitness should be similar between habitats if habitat selection follows an ideal free distribution; fitness should be dissimilar between habitats if habitat selection is modified by territorial behavior. I tested these assumptions by examining a variety of fitness estimates obtained from white-footed mice living in nest boxes in forest, forest edge and fencerow habitats in southwestern Ontario. As expected, mean litter size declined with increased population density. Litter sizes, adult longevity and the proportion of adult animals in breeding condition were not significantly different among the three habitats. The success at recruiting at least one offspring to the adult population and the number of recruits per litter were much greater in the forest than in either of the other two habitats. Fitness was thus unequal among habitats and the results confirm both assumptions of density-dependent habitat selection theory for territorial white-footed mice.     

Why Seychelles Warblers fail to recolonize nearby islands: unwilling or unable to fly there?

The Seychelles Warbler Acrocephalus sechellensis is a rare island endemic which, from 1920 to 1988, occurred only on Cousin Island (29 ha) in the Seychelles. Despite the saturated nature of this population and the possibility of obtaining higher reproductive success on new nearby islands, inter-island dispersal by Seychelles Warblers is extremely rare (0.10%). We test the hypothesis that Seychelles Warblers show an adaptation typical for island birds: a low-cost reduced-size flight apparatus. We compared the anatomy of the flight apparatus (wing shape, wing loading, skeletal parts and musculature) of Seychelles Warblers with that of three closely related migratory Acrocephalus species (Eurasian Reed Warbler A. scirpaceus , Australian Reed Warbler A. australis and African Reed Warbler A. baeticatus ). Seychelles Warblers do not differ from the migratory warblers in pectoral mass and skeletal attachment area relative to body mass, wing shape and wing loading. Seychelles Warblers show the morphological structures required for sustained flight, but may have the behavioural reluctance to cross what they may regard as extensive bodies of water.     

Microsatellite determination of male reproductive success in a natural population of the territorial ornate dragon lizard, Ctenophorus ornatus

It is now evident that the genetic mating system can be very different to the observed mating system. However, it is less well known what makes particular individuals more (or less) successful than expected from the observed system. In this study the observed territorial structure of a field population of the agamid lizard, Ctenophorus ornatus, was compared with the mating system as evidenced by microsatellite parentage assignment. This study also investigated whether any male traits predicted reproductive success. Sixty-five per cent of clutches were sired at least partially by a male other than the main territory-holding male and 35% of clutches were sired by a male with no overlap of the female's territory. Multiple paternity was moderately frequent at 25% of clutches. Male chest patch size predicted territory size and the number of females in the territory, but did not predict reproductive success. Instead, male head depth and body size were independently related to the number of offspring sired. As male head depth also predicted the number of females in a territory, these males are likely to be gaining increased reproductive success as a consequence of the higher number of females in their territories. Larger body size males, however, did not have a greater number of females in their territory and instead had more extra-territorial copulations. Whether these extra-territorial copulations are due to female choice or success in male competition is unknown.     

Territory quality determines social group composition in Ethiopian wolves Canis simensis

1. We contrast the value of four different models to predict variation in territory size as follows: resource density (the ideal free distribution), population density, group size and intruder pressure (relative resource-holding potential). In the framework of the resource dispersion hypothesis, we test the effect of resource abundance and spatial variation in resource distribution on the age/sex composition of social groups. 2. We explore these drivers of territory size and group size/composition in Ethiopian wolves Canis simensis in the Bale Mountains, Ethiopia, using fine-scale distribution maps of their major prey species based on satellite-derived vegetation maps. 3. The number of adult males is correlated with territory size, while prey density, wolf population density and intruder pressure are not associated with territory size. On average, each additional adult male increases territory size by 1.18 km(2). 4. Prey abundance increases with territory size (average biomass accumulation of 6.5 kg km(-2)), and larger territories provide greater per capita access to prime foraging habitat and prey. 5. The age/sex composition of wolf packs is more closely related to territory quality than territory size. Subordinate adult females are more likely to be present in territories with greater proportions of prime giant molerat Tachyoryctes macrocephalus habitat (i.e. >80% of Web Valley territories and >20% in Sanetti/Morebawa), and more yearlings (aged 12-23 months) occur in territories with greater overall prey biomass. 6. Wolf packs with restricted access to good foraging habitat tend to defend more exclusive territories, having a lower degree of overlap with neighbouring packs. 7. The greater per capita access to prey in large groups suggests a strong evolutionary advantage of collaborative territorial defence in this species, although the relative costs of territorial expansion vs. exclusion depend upon the spatial distribution of resources. We propose a model whereby territory size is determined by the number of adult males, with the presence of subordinate females and yearlings dependent on the quality of habitat, and the abundance and distribution of prey, incorporated within territory boundaries.     

Population regulation by habitat heterogeneity or individual adjustment?

1. The habitat heterogeneity (HHH) and individual adjustment (IAH) hypotheses are commonly proposed to explain a decrease in reproduction rate with increasing population density. Higher numbers of low-quality territories with low reproductive success as density increases lead to a decrease in reproduction under the HHH, while more competition at high density decreases reproduction across all territories under the IAH. 2. We analyse the influence of density and habitat heterogeneity on reproductive success in eight populations of long-lived territorial birds of prey belonging to four species. Sufficient reliability in distinguishing between population-wide, site-specific and individual quality effects on reproduction was granted through the minimal duration of 20 years of all data sets and the ability to control for individual quality in five of them. 3. Density increased in five populations but reproduction did not decrease in these. Territory occupancy as a surrogate of territory quality correlated positively with reproductive success but only significantly so in large data sets with more than 100 territories. 4. Reproductive success was always best explained by measures of territory quality in multivariate models. Direct or delayed (t-1) population density entered very few of the best models. Mixed models controlling for individual quality showed an increasing reproductive performance in older individuals and in those laying earlier, but measures of territory quality were also always retained in the best models. 5. We find strong support for the habitat heterogeneity hypothesis but weak support for the individual adjustment hypothesis. Both individual and site characteristics are crucial for reproductive performance in long-lived birds. Proportional occupancy of territories enables recognition of high-quality territories as preferential conservation targets.     

Multiple Plumage Ornaments as Signals of Intrasexual Communication in Golden‐Winged Warblers

Avian plumage represents some of the greatest diversity in integument coloration of all animals. Plumage signals are diverse in function, including those that allow for assessing potential mates or the mitigation of agonistic interactions between rivals. Many bird species possess multiple ornamental traits that have the potential to serve as multiple or redundant signals. For example, male golden‐winged warblers (Vermivora chrysoptera) have brilliant carotenoid‐based yellow crowns, melanin‐based black throats, and structurally based white patches on their outer tail feathers. Using a correlative approach, we investigated whether plumage ornaments have the potential to reliably signal ability to acquire higher quality territory, aggressive response to simulated territorial intrusions, and reproductive success. We found that both crown chroma and tail brightness were significantly related to habitat quality and aggression; more ornamented birds held territories with higher quality habitat and were less aggressive toward simulated conspecific stimuli. Older birds sang less threatening songs than younger birds and were more likely to sing their mate attraction song type (type 1) rather than songs typically reserved for agonistic interactions (type 2). Finally, despite our previous research demonstrating that habitat strongly predicts reproductive success in this warbler population, we found no evidence of a direct link between ornamentation and reproductive success. Overall, these data suggest that younger males, and those with lower quality ornaments, compensate with more aggressive behaviors. Additional research is needed to investigate the dynamics between behavioral traits and ornaments to better understand complex signaling and how golden wing signals function in conspecific interactions (male–male interactions and mate‐choice).     

Territory quality affects the relative importance of habitat heterogeneity and interference competition in a long‐lived territorial songbird

Density‐dependent reproduction is commonly explained by either the habitat heterogeneity (HHH) or individual adjustment (IAH) hypothesis. Under the HHH, high quality territories are assumed to be occupied first. At higher density, occupation of low‐quality territories increases due to lower availability of high‐quality territories, which reduces mean reproductive success. Alternatively, the IAH assumes that increased competition at higher densities reduces reproductive success in all territories. For birds of prey, HHH plays an important role in territorial species, and IAH in socially breeding species. To test the generality of this hypothesis, we studied the mechanism behind density dependence in raven Corvus corax, a long‐lived passerine bird, using long‐term population data from a large number of territories. Population density decreased reproduction, which was explained by increased usage of low quality territories at higher density, supporting the HHH. Density reduced reproduction in low quality territories, but not in high and intermediate quality territories. We additionally compared the explanatory power of different models describing brood size, representing IAH, HHH, or a combination of both. The best model represented a combination of both hypotheses, in which the effect of density depended on territory quality. Our conclusion that both IAH and HHH are supported can be explained by the biology of ravens, where territorial adults not only experience interference competition with other territorial adults, but also with social groups of juveniles and floaters. We conclude that the relative importance of IAH and HHH may depend on variation in territory quality and social structure.     

Experimental evaluation of sex differences in territory acquisition in a cooperatively breeding bird

In many species, territory ownership is a prerequisite for reproduction;consequently, factors that affect success in territory acquisitioncan have a large impact on fitness. When competing for territories,some individuals may have an advantage if, for example, theyare phenotypically superior or more familiar with the site thanothers. The relative importance of the many factors involvedin territory acquisition is, at present, unclear. We studiedpatterns of natural territory acquisition in a closed and saturatedpopulation of Seychelles warblers. Furthermore, by removingbreeders, we experimentally investigated the relative importance,to territory acquisition, of a range of factors and assessedwhether this differed between the sexes. In both sexes, themain route to natural territory acquisition was to dispersefrom the natal territory to immediately claim a vacant dominantposition. Males were older than females when acquiring a territoryfor the first time. In the removal experiment, for both sexes,the proximity of an individual's natal territory to a vacantdominant position was positively related to the individual'schance of claiming the vacancy. Older males were more likelyto gain an experimental vacant dominant position than were youngmales, whereas age did not affect territory acquisition in females.In the Seychelles warbler, the degree of intrasexual competitionfor territory ownership may be stronger for males than for femalesbecause territory ownership is a prerequisite for male reproduction,whereas females can reproduce on their natal territory. In suchcompetition, young males subsequently lose out to older ones.     

Constrained by available raptor hosts and islands: density-dependent reproductive success in red-breasted geese

In this paper we aim to explain the distribution of red-breasted geese Branta ruficollis over different nesting habitats. To be safe from land predators red-breasted goose colonies were restricted to i) islands on rivers, ii) cliffs with peregrine falcons Falco peregrinus , and iii) the close proximity of snowy owl Nyctea scandiaca and rough-legged buzzard Buteo lagopus nests. Among years nest site availability varied by fluctuations in numbers of owls and buzzards in association with cycles in lemming abundance, but the total number of goose nests found in the study area did not vary. The distribution of geese, in combination with data on reproductive success, suggested a despotic mechanism: at cliffs, goose numbers were constant among years with an invariably high reproductive success, whereas large fluctuations in numbers on islands coincided with opposite trends in success. Apparently, geese nesting with owls or buzzards moved to the few islands present in the study area during years when these birds of prey were absent. Consequently, in such years the average density of geese on islands was more than twice as high as at cliff colonies (5.4 and 2.3 pairs per ha of foraging habitat, respectively). Colony size at cliffs may have been restricted by territorial behaviour of the geese, though there is evidence that, additionally, the host falcons also limited the number of nesting geese. Apparently rare in closely related species, we observed a negative density-dependent effect on reproductive success during the nest phase, and attribute this to limited food resources, reinforced by the high frequency of territorial interactions. This leads to the conclusion that, in addition to predation pressure, nesting density is an important agent in the link between lemming cycles and goose breeding success.     

Territorial defense, territory size, and population regulation

The carrying capacity of an environment is determined partly by how individuals compete over the available resources. To territorial animals, space is an important resource, leading to conflict over its use. We build a model where the carrying capacity for an organism in a given environment results from the evolution of territorial defense effort and the consequent space use. The same evolutionary process can yield two completely different modes of population regulation. Density dependence arises through expanding and shrinking territories if fecundity is low, breeding success increases gradually with territory size, and/or defense is cheap. By contrast, when fecundity is high, breeding success sharply saturates with territory size, and/or defense is costly, we predict fixed territory sizes and regulation by floaters. These "surplus" individuals form a buffer against population fluctuations. Yet floaters can also harm breeder performance, and by comparing population growth of a territorial population to a nonterritorial (and individually suboptimal) alternative, we can quantify the harmful effect of evolutionary conflict on population performance. Territoriality has often been found to increase population stability, but this may come at a cost of reduced equilibrium densities.