Defence, intrusion and the evolutionary stability of territoriality

Territorial behaviour can only be adaptive if its costs are outweighed by its benefits. Territorial individuals incur costs by defending their territories against intruders. Usually these intruders are assumed to be non-territorial floaters attempting to take over the whole territory or neighbours trying to extend the borders of their own territory. We instead investigate how costs and benefits of territorial behaviour are affected by neighbours which invade to steal resources on a territory.We show analytically that in the absence of defence intrusion into neighbouring territories always pays and that even if territories are defended intrusion levels can still be high. Using a more detailed simulation model we find that territory defence usually disappears from the population even if owners have a strong advantage over intruders in terms of fighting costs or foraging efficiency. Defence and thus territoriality can only be evolutionarily stable if fighting costs for the intruder relative to the productivity of the territory are very high or if crossing the borders between territories carries additional costs.Our results show that stealing of resources by neighbours can have a considerable effect on the evolutionary stability of territory defence and thus territoriality itself. A more mechanistic model of territorial behaviour is needed to incorporate these kinds of mechanisms into a general theory on the evolution of territoriality.     

Access to mates in a territorial ungulate is determined by the size of a male's territory, but not by its habitat quality

1. Territoriality is commonly associated with resource defence polygyny, where males are expected to gain access to females by anticipating how resources will influence female distribution and competing for resource-rich sites to establish their zone of dominance. 2. We tested this hypothesis in European roe deer (Capreolus capreolus) by simultaneously assessing the influence of resources on female distribution and the influence of female distribution on male distribution and breeding success using paternity analyses. 3. Females did not fully distribute themselves among male territories in relation to resources. As a result, relative female abundance in a male's territory depended on territory size, but not on its habitat quality. In turn, relative female abundance in a male's territory determined, at least partially, his breeding success. 4. Interestingly, male territory size, and hence access to females, was partly determined by male body mass (all males) and by residual antler size (subadults only). The latter result suggests that large antlers may be important to young males for establishing their first territory, which is then usually retained for all subsequent reproductive seasons. 5. To conclude, although territoriality of male roe deer has certainly evolved as a tactic for ensuring access to mates, our results suggest that it does not really conform to a conventional resource defence polygyny strategy, as males seem to gain no obvious benefit from defending a territory in an area of high habitat quality in terms of enhanced access to mates. 6. This may explain the stability of male territories between years, suggesting that male territoriality conforms to an 'always stay' and 'low risk-low gain' mating strategy in roe deer.     

Why are Male Columbian Ground Squirrels Territorial?

Male territorial defence is a component of many vertebrate mating systems and is often regarded as a tactic for acquiring mates. Traditionally considered within the context of overt site‐specific defence, territoriality actually may have several components which encompass a variety of behavioural tactics (e.g. post‐copulatory mate‐guarding, defence of resources that females need, defence of area around females) that underlie a mating system. The purpose of our study was to evaluate such influences on the territorial behaviour of male Columbian ground squirrels in southwestern Alberta, Canada. Males were dominant and territorial if they defended a minimum convex polygon activity range by chasing other males more within the activity range than they were chased. Subordinate males had no territory and were chased throughout their ranges, but they competed for mates by increasing chases in their activity range when nearby females were oestrous. Dominant males exhibited conditional breeding tactics, tending to chase other dominant males from their territory when nearby females were oestrous, but travelling outside their activity ranges to chase subordinate males when females were not oestrous. Although females mated first with a dominant male on whose territory they resided (and in order from oldest to youngest if several territories overlapped), mating pairs were not exclusive, as females usually mated with additional males. Males also guarded females after copulation and defended females directly just before oestrus, rather than defending territory per se during those times. Thus, males possess a repertoire of behaviours that complement site‐specific territoriality, and territory ownership serves to facilitate a first mating with females that live on the territory.     

Butterflyfish social behaviour,with special reference to the incidence of territoriality: a review

Synopsis Butterflyfishes (Chaetodontidae) are among the best studied of coral reef fishes. Feeding ecology and some aspects of behaviour have been firmly established. However, spacing behaviour remains controversial. Two major studies made in the 1970s concluded that the majority of species were not territorial. We suggest that these and other studies which have concluded that territories are not held have generally suffered from short observation periods, and have not mapped the ranges occupied by individuals. Further, low frequencies of agonistic behaviour have been interpreted as evidence of non-territoriality. By contrast, studies which have proven territoriality have had long observation periods and have mapped ranges. These have shown that territories are usually maintained with very little overt aggression. Spacing behaviour and feeding behaviour are clearly linked, with territoriality common among benthic-feeding species, especially obligate corallivores. Species with broad dietary flexibility tend to have flexible social systems, while plankton feeders are usually gregarious. The widespread occurrence of monogamy in butterflyfishes appears linked to territoriality, the majority of territorial species identified to date occurring predominantly as pairs. Data currently available suggest that this is because pair defence of the territory is more efficient than by individuals. However, several alternative hypotheses for the evolution of monogamy based on spawning constraints and predation risk cannot yet be ruled out.     

Territorial Behaviour and Social Organization as a Function of the Level of Aggressiveness in Male Mice

Territoriality and social organization were examined in relation to different genetic dispositions for aggressive behaviour. The animals used in the study were male mice of the 51st and 52nd generation of selection for high (Turku Aggressive, TA) and low (Turku Non-Aggressive, TNA) levels of aggressiveness. The level of aggressiveness of the animals was assessed by means of individual tests with non-aggressive standard opponents, after which they were allowed to form individual territories in a 102 times 204 times 90 cm enclosure. TA and TNA males were placed in different enclosures. After 2 wk, when the partitions between individual pens were removed, the behaviour of the animals was observed for a 7-d period. Excessive fighting between the highly aggressive TA males occurred, resulting in the formation of dominant-subordinate relationships. A great number of attacks inflicted were found to be associated with dominance in the colony, and correlated with a high level of aggressiveness when the animals were individually tested for aggression after having been in colony environments. The level of aggressiveness of the TA males that had become subordinates had significantly decreased. The TNA males fought less and were more often found to stay in their original territory for the entire period of observation. The results suggest that different genotypes for aggression arc related to differences in territoriality and social organization in mice.     

Winter territoriality of Mute Swans Cygnus olor

There was considerable variation in winter territoriality among Mute Swan pairs around Oxford, though most pairs maintained their territories for at least half the winter. Variation was associated with temperature and with territory quality pairs left their territories most commonly during the coldest months of the winter, and pairs on good territories, with abundant vegetation and accessible pasture. stayed longer on territory than those on poor territories with sparse vegetation and little pasture. As in other species, exclusive territorial defence was maintained at intermediate levels of resource availability, and flocks were able to settle on a few particularly good territories. Circumstantial evidence suggested that winter territories may be maintained not only to provide an adequate food supply for the owners but also to ensure access to a brerding site by preventing other individuals from taking over the area.     

Territorial and foraging behaviour of two corallivorous butterflyfishes

The territorial and foraging behaviour of two Red Sea butterflyfish species was studied at three sites in the Gulf of Aqaba. Chaetodon austricaus , a generalist corallivore that exploited evenly distributed food resources, maintained exclusive pair territories. Individuals fed by grazing for brief periods on a coral colony before moving to the next. In contrast, C. trifascialis , a specialist corallivore that exploited patchily distributed food resources, demonstrated considerable variation in territorial behaviour that ranged from the defence of exclusive solitary territories, to the shared use of a large home range. Individuals showed highly variable feeding behaviour, from grazing analogous to C. austriacus , to continual use of a single large coral colony. The results of this study demonstrate how the use of space by individuals depends critically upon the distribution of key food resources. In addition, the results demonstrate that foraging behaviour of territorial butterflyfish can be quite plastic, and adapt to local conditions.     

FOOD RESOURCES, TERRITORY DENSITY AND REPRODUCTIVE SUCCESS OF AN ISLAND SILVEREYE POPULATION ZOSTEROPS LATERALIS

We examined the relationships between food resources, territory density and some breeding parameters (individual reproductive success and parental age) of a Capricorn Silvereye population during two years' detailed study on Heron Island, Great Barrier Reef. The territorial behaviour of the Silvereyes included dawn song. aggression and distinctive vocalizations. During both years, about 85% of pairs occupied territories although the population sizes differed. The dispersion pattern of territories was not regular and was correlated with the density of figs and human food scraps. Nestlings were fed more figs as they grew, and the parents foraged in fig trees outside their territories. However, only about 60%, of territorial pairs fledged young. Pairs which fledged most young were older, fed more insects to their nestlings, and nested in areas containing more fruiting fig trees per territory. We conclude that food resources were in short supply, and that access to fig trees provided breeding birds with a quick energy source while they searched for insect protein for the young. The data are consistent with the predictions of the ‘sufficient resource‘ hypothesis of the adaptive significance of territoriality but not with its assumption that the principal benefit is the food within the territory.     

Dominance hierarchies in group-living cleaning gobies: causes and foraging consequences

In species living in social groups, aggression among individuals to gain access to limiting resources can lead to the formation of stable social hierarchies. We tested whether dominance rank in social groups of sponge-dwelling cleaning gobies Elacatinus prochilos in Barbados was determined by physical attributes of individuals or by prior experience of dominance, and examined the foraging consequences of dominance rank. Intraspecific aggression within groups resulted in stable dominance hierarchies that were strongly correlated with fish length. Dominant individuals maintained exclusive territories while subordinate fish occupied broader home ranges. Larger, competitively dominant fish were able to monopolize areas inside the sponge lumen with the highest abundance of the polychaete Haplosyllis spp., a favoured prey item, and achieved the highest foraging rates. The removal of a territorial individual from large groups resulted in a domino-like effect in territory relocation of the remaining fish as individuals moved to the territory previously occupied by the individual just above them in the group hierarchy. Individuals added to existing groups generally failed to gain access to territories, despite being formerly dominant in their original groups. When given the opportunity to choose a location in the absence of larger competitors, gobies frequently preferred positions that were previously defended and that had abundant food. These results suggest that intraspecific competition for resources creates the observed dominance structures and provides support for the role of individual physical attributes in the formation and maintenance of dominance hierarchies.     

Do Feeding Resources Induce the Adoption of Resource Defence Polygyny in a Lekking Butterfly?

Among polygynous species, males often compete for the possession of mating sites to increase their reproductive success. Weaker individuals frequently adopt alternative non‐territorial mate‐locating tactics, but the adoption of alternative territorial tactics may also occur. Although alternative tactics with territory defence are less common in arthropods, factors that drive its adoption may provide information to understand the organization of different territorial mating systems in the group. Here we investigate the adoption of resource‐based territoriality as an alternative to a non‐resource‐based one by males of the butterfly Paryphthimoides phronius. Male P. phronius commonly defend sunny clearings lacking feeding resources in the forest edge (non‐resource‐based territoriality). However, after experimentally offering fermenting fruit in previously undefended sites, we showed that males also adopt a resource defence tactic. Males in territories with fermenting fruits apparently feed on this resource when they are not defending the territory. However, males in sites without resources did not migrate to territories with resources when given the opportunity. To our knowledge, this is the first experimental investigation to show a non‐resource‐ and an alternative resource‐based mate‐locating tactic in a butterfly. We suggest that this behavioural flexibility may represent an important step to understand the ecological factors responsible for the organization and evolution of different territorial mating systems in insects.     

The ontogeny of territoriality during maturation

Territoriality drives the evolution of many mating systems, yet has remained an extremely difficult trait to measure in the wild. Classic studies rely on the theoretical framework of resource holding potential (RHP) as a predictor of success in territory acquisition. However, mounting evidence suggests that an individual's RHP may change over short time scales. Previous studies suggest that RHP is best understood by considering two categories of territoriality, resource defending and resource usurping potential (RDP and RUP, respectively). In a population of the side-blotched lizard, Uta stansburiana, blue-throated males defend territories near their natal site (RDP) while mature orange-throated males use their RUP to sequester high quality territories from defending territorial males. We tested differences in territoriality by releasing pairs of maturing male lizards onto experimentally altered territories that had improved thermal qualities owing to the addition of rock piles. Dyads of males competed for these thermal resources and the females that were released on rock piles. Early in the season, when throat colors were not yet fully expressed, large male body size predicted contest victories irrespective of throat color. This pattern changed however, with the onset of the breeding season and maturation of throat color. Orange males tended to usurp territories from blue males within 2 weeks of contest initiation. Large male body size still influenced these contests, but after one more week, throat color was the sole factor explaining variance in territory ownership. We demonstrate the ontogeny of territoriality relating to body size and throat color during maturation, and suggest a novel approach to assessing territoriality and aggression in the wild.     

THE ECOLOGY OF THE GREENISH WARBLER PHYLLOSCOPUS TROCHILOIDES IN ITS WINTER QUARTERS

The Greenish Warbler is an abundant entirely insectivorous Pafaearctic migrant wintering in the tropical deciduous forests of India and east Asia. A population was studied at one locality in the eastern Ghats of south India over one winter, with a short return the following winter. Individuals maintain, and annually re-occupy, territories throughout their seven or eight months stay. A general account of territorial behaviour is given.
There is much evidence that food is critically short, particularly during the months of December to February and March, which coincides with the end of the dry season. Because of the short duration of the study, there are shortcomings in data presented. Nevertheless there is evidence that territories vary severalfold in quality and individual birds' behaviour and survival probability are correlated with this. It is suggested that territorial behaviour is the best individual strategy for long-term resource management. The presence of food competitors can alter this behaviour, much as changes in food dispersion are known to. The ability to control return time to a patch as a subsidiary function for territoriality is briefly discussed.     

TERRITORIALITY IN THE COMMON SHELDUCK TADORNA TADORNA

A population of Common Shelducks on the Ythan Estuary was studied intensively from December 1961 to August 1964, with special attention to territoriality and population regulation.
Many of the shelducks in this population establish mutually exclusive territories; the others (usually about one third of the population) remain together in a communal flock. Both members of territorial pairs take part in territorial defence.
Territory size is determined by the immediate topography of the area and by the limits of tolerance of the owner. The distribution of territories was found to be related to the distribution of Hydrobia ulvae , which is the staple item in the shelducks' diet.
Territories were usually occupied by the same birds year after year. The number of territories remained constant at 71 ± 1 throughout the three years of the study.
The first birds to return in the spring were not necessarily the first to take up their territories. Some territories were left unclaimed (at least for the greater part of the day) until the end of April. At no time were interlopers or neighbours ever seen trying to establish themselves in these unoccupied territories.
Territories from which both birds were experimentally removed were reoccupied by birds from the surplus flock, usually within a matter of days. When females of territorial pairs were removed, the surviving males invariably deserted their territories, but when the males were removed, the females remained on their territories and eventually acquired new mates.     

Acoustic Monitoring Reveals Congruent Patterns of Territorial Singing Behaviour in Male and Female Tropical Wrens

Many animals defend territories against conspecific individuals using acoustic signals. In birds, male vocalizations are known to play a critical role in territory defence. Territorial acoustic signals in females have been poorly studied, perhaps because female song is uncommon in north‐temperate ecosystems. In this study, we compare male vs. female territorial singing behaviour in Neotropical rufous‐and‐white wrens Thryothorus rufalbus, a species where both sexes produce solo songs and often coordinate their songs in vocal duets. We recorded free‐living birds in Costa Rica using an eight‐microphone Acoustic Location System capable of passively triangulating the position of animals based on their vocalizations. We recorded 17 pairs of birds for 2–4 consecutive mornings and calculated the territory of each individual as a 95% fixed kernel estimate around their song posts. We compared territories calculated around male vs. female song posts, including separate analyses of solo vs. duet song posts. These spatial analyses of singing behaviour reveal that males and females use similarly sized territories with more than 60% overlap between breeding partners. Territories calculated based on solo vs. duet song posts were of similar size and similar degrees of overlap. Solos and duets were performed at similar distances from the nest for both sexes. Overall, male and female rufous‐and‐white wrens exhibit very similar spatial territorial singing behaviour, demonstrating congruent patterns of male and female territoriality.     

Agonistic Behaviour and Development of Territoriality During Ontogeny of the Sea Anemone Dwelling Crab Allopetrolisthes Spinifrons (H. Milne Edwards, 1837) (Decapoda: Anomura: Porcellanidae)

Allopetrolisthes spinifrons is an ectosymbiotic crab of the sea anemone Phymactis clematis. As a consequence of low host abundance, these represent a scarce and limited resource for the crab. Additionally, the relatively small size of the sea anemone host suggests that few symbiotic crabs can cohabit on one host individual, forcing crabs to adopt a territorial behaviour. In order to examine the potential presence and ontogenetic development of territoriality, the agonistic behaviour between crabs of various ontogenetic stages (adults, juveniles, and recruits) was studied in the laboratory. Laboratory experiments demonstrated that adult or juvenile crabs aggressively defended their sea anemone hosts against adult or juvenile intruders, respectively, but both adult and juvenile crabs tolerated recruits. Adult crabs behaved indifferently towards juvenile crabs, sometimes tolerating them, sometimes expelling them. Recruits never showed agonistic behaviour among themselves. The agonistic interactions observed in the laboratory and the uniform population distribution pattern on sea anemones recently described for A. spinifrons indicate that this species exhibits territorial behaviour, which develops during ontogeny. Territoriality in this species and other symbiotic decapods may function as a density-dependent mechanism of population regulation, being mediated by the availability of hosts. Resource monopolisation behaviours may be common among other symbiotic and free-living marine invertebrates inhabiting discrete habitats that represent a limiting resource.     

Heritable variation for territorial success in two Drosophila melanogaster populations

Male fruitflies from stocks from two localities were artificially selected for defence of a food area against intruding males. Both stocks showed a rapid replicable response to selection over a few generations, indicating considerable genetic variation for territorial success in the base populations. Crosses between lines indicate directional dominance for increased territorial success and no maternal or paternal effects. Selected males escalated relatively more frequently against territory residents than control males, and won relatively more escalated encounters. There was no correlated response in body weight. In the presence of territories, selected males had a higher mating success with inseminated females than control males, but did not differ in mating speed. Indirect selection for territorial success was carried out by allowing flies to mate in the presence of different types of resources. After 21–26 generations, males from lines held in cages with discrete resources where territories could be established had greater territorial success than males from lines held in cages with one large resource. This genetic divergence in response to resource type is consistent with the heritable variation in territorial success and mating success of territorial males.     

Territoriality of Giant Otter Groups in an Area with Seasonal Flooding

Territoriality carries costs and benefits, which are commonly affected by the spatial and temporal abundance and predictability of food, and by intruder pressure. Giant otters (Pteronura brasiliensis) live in groups that defend territories along river channels during the dry season using chemical signals, loud vocalizations and agonistic encounters. However, little is known about the territoriality of giant otters during the rainy season, when groups leave their dry season territories and follow fish dispersing into flooded areas. The objective of this study was to analyze long-term territoriality of giant otter groups in a seasonal environment. The linear extensions of the territories of 10 giant otter groups were determined based on locations of active dens, latrines and scent marks in each season. Some groups overlapped the limits of neighboring territories. The total territory extent of giant otters was correlated with group size in both seasons. The extent of exclusive territories of giant otter groups was negatively related to the number of adults present in adjacent groups. Territory fidelity ranged from 0 to 100% between seasons. Some groups maintained their territory for long periods, which demanded constant effort in marking and re-establishing their territories during the wet season. These results indicate that the defense capacity of groups had an important role in the maintenance of giant otter territories across seasons, which may also affect the reproductive success of alpha pairs.     

Agonistic Behaviour and Development of Territoriality During Ontogeny of the Sea Anemone Dwelling Crab Allopetrolisthes Spinifrons (H. Milne Edwards, 1837) (Decapoda: Anomura: Porcellanidae)

Allopetrolisthes spinifrons is an ectosymbiotic crab of the sea anemone Phymactis clematis . As a consequence of low host abundance, these represent a scarce and limited resource for the crab. Additionally, the relatively small size of the sea anemone host suggests that few symbiotic crabs can cohabit on one host individual, forcing crabs to adopt a territorial behaviour. In order to examine the potential presence and ontogenetic development of territoriality, the agonistic behaviour between crabs of various ontogenetic stages (adults, juveniles, and recruits) was studied in the laboratory. Laboratory experiments demonstrated that adult or juvenile crabs aggressively defended their sea anemone hosts against adult or juvenile intruders, respectively, but both adult and juvenile crabs tolerated recruits. Adult crabs behaved indifferently towards juvenile crabs, sometimes tolerating them, sometimes expelling them. Recruits never showed agonistic behaviour among themselves. The agonistic interactions observed in the laboratory and the uniform population distribution pattern on sea anemones recently described for A . spinifrons indicate that this species exhibits territorial behaviour, which develops during ontogeny. Territoriality in this species and other symbiotic decapods may function as a density-dependent mechanism of population regulation, being mediated by the availability of hosts. Resource monopolisation behaviours may be common among other symbiotic and free-living marine invertebrates inhabiting discrete habitats that represent a limiting resource.     

Correlates of Territoriality in Rutting Red Deer

The mating strategy most commonly reported for male red deer, Cervus elaphus, is the defence of females (harems), territoriality having been described only in Doñana, Spain. We observed rutting males at five different populations in Spain and during 4 consecutive yr in Doñana. Female defence was the only strategy observed in two of the populations, whereas territorial defence coexisted with female defence in the remaining three populations. Territorial defence appeared to be more costly than female defence, in terms of rates of aggressive interaction, and territorial males tended to gather more females per d than non-territorial ones. Both mating strategies seemed to respond to local variations in habitat, which in turn affected female distribution. Females concentrated in areas with high-quality forage, and most territories contained patches of high-quality food (i.e. greater quality within boundaries) or were located along main routes used by females. The results are interpreted in the light of environmental conditions in southern Europe, where the rut coincides with the less favourable season for herbivores (in terms of food resources) after the hot and dry summer. Under such conditions of food scarcity coupled with patchy distribution, females tend to concentrate on the remaining patches of green swards, and males benefit from defending the food resources that attract females.