Competitor density influences resource defence in a Poeciliid fish

The concept of economic defendability states that individuals will only defend resources when the benefits outweigh the costs. Competitor density is one factor that influences resource defence among fishes, resource defence being predicted to be highest at intermediate competitor densities and reduced at higher and lower densities, producing a dome shaped relationship. We investigated the effects of competitor density using male swordtails, which form dominance hierarchies and have already been demonstrated to defend a food resource. We found that both aggression (F_2,32 = 5.392; P = 0.010) and time at a food resource (F_2,32 = 3.574; P = 0.040) vary with differences in competitor density, and that the frequency of aggression significantly predicts time at the food resource only at an intermediate density (P = 0.033; r²adj = 0.219). The ability to vary the level of defence with respect to the immediate environment may result in fitness benefits to male swordtails. Further studies examining changes in behaviour over time and examining interacting influencing factors would be beneficial.     

Female–female aggression is linked to food defence in a poison frog

Habitat occupancy by territorial animals is expected to depend on the distribution of critical resources. Knowledge on female territoriality is scarce, but it has been suggested as a mechanism to defend limited resources for reproduction. A previous study showed female intrasexual aggression to be associated with territorial behaviour in the strawberry poison frog Oophaga pumilio, a diurnal aposematic species with complex maternal care. Here, we investigate the link between spatial distribution of resources important for reproduction and female distribution and behaviour. We observed focal females in their natural habitat in Costa Rica, and recorded the distribution of ecological predictor variables in a grid system. We used the data for calculating home range and territory sizes and for connecting female habitat use to the distribution of potential resources by computing spatial habitat occupancy models. Even though we found females to occupy large home ranges, they were highly aggressive towards other females only inside a small part of their home range, here termed core area. Among the ecological factors, the sustained abundance of ants (main food item of the frogs), the presence of leaf litter and suitable rearing sites for tadpoles predicted female site occupancy patterns. The number of ants per grid was twice as high in the core areas compared to the rest of the female home ranges. Our results suggest that female spacing behaviour is principally driven by the spatial distribution of its main food resource, but that hiding places (leaf litter) and tadpole‐rearing sites also play a role. The defence of areas with sustainably high abundance of ants could be relevant, as egg production and maternal care are energetically highly demanding in this prolonged‐breeding species. Regarding the link between resource defence and maternal care, the reproductive strategy of female strawberry poison frogs resembles that of the females of small mammals comprising same‐sex competition for food and high investment in producing and rearing young.     

Resource Defence or Exploded Lek? – A Question of Perspective

It becomes increasingly obvious that animal mating systems cannot be classified into distinct categories, but transitions between mating system classes are continuous. Positioning a certain mating system at this continuum is often not straightforward, however. Depending on which characteristic is considered, a mating system may end up at very different positions on this gradient. Here, we explore the potential conflict between mating system classifications that may arise when they are based on different criteria by investigating the mating system of the cichlid fish Simochromis pleurospilus in which males defend small patches of homogeneously distributed food resources (turf algae) vigorously against food competitors, but they allow specific females to use them. We hypothesized that male defence may generate high‐quality feeding patches serving to attract females, and hence male territoriality constitutes a form of courtship. Our field data show that males selectively allow approximately one‐third of the visiting females to feed on their territory and that females preferentially feed in male territories and usually sample several territories successively. As males protect food patches against other algae grazers and guard females from harassment by food competitors, females gain nutritional benefits from visiting male territories. Hence, males appear to generate essential resources for females, which is the key feature of resource‐defence mating systems, although the distributions of resources and of males and females are characteristics of an exploded lek.     

Home range,activity and sociality of a top predator,the dingo: a test of the Resource Dispersion Hypothesis

The idea that groups of individuals may develop around resource patches led to the formulation of the Resource Dispersion Hypothesis (RDH). We tested the predictions of the RDH, within a quasi‐experimental framework, using Australia’s largest terrestrial predator, the dingo Canis lupus dingo. Average dingo group sizes were higher in areas with abundant focal food sources around two mine sites compared with those in more distant areas. This supports the notion that resource richness favours larger group size, consistent with the RDH. Irrespective of season or sex, average home range estimates and daily activity for dingoes around the mine sites were significantly less than for dingoes that lived well away. Assuming that a territory is the defended part of the home range and that territory size is correlated with home range size, consistent with the RDH, the spatial dispersion of food patches therefore determined territory size for dingoes in our study. However, although sample size was small, some dingoes that accessed the supplementary food resource at the mines also spent a large proportion of their time away, suggesting a breakdown of territorial defence around the focal food resource. This, in combination with the large variation in home range size among dingoes that accessed the same supplementary food resource, limits the predictive capabilities of the RDH for this species. We hypothesize that constraints on exclusive home range occupancy will arise if a surfeit of food resources (in excess of requirements for homeostasis) is available in a small area, and that this will have further effects on access to mates and social structure. We present a conceptual model of facultative territorial defence where focal resources are available to demonstrate our findings.     

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.     

Determinants of reproductive success in voles: space use in relation to food and litter size manipulation

Spacing behaviour of female mammals is suggested to depend on the distribution and abundance of food. In addition, food limitation has been found to constrain the reproductive success of females. However, whether females maximize their reproductive success by adjusting space use in relation to current food availability and reproductive effort (e.g. litter size) has not been experimentally studied. We examined these questions by manipulating simultaneously food resources (control vs. food supplementation) and litter sizes (control vs. plus two pups) of territorial female bank voles (Clethrionomys glareolus) in large outdoor enclosures. Females with supplementary food had smaller home ranges (foraging area) and home range overlaps than control females, whereas litter size manipulation had no effect on space use. In contrast, the size of territory (exclusive area) was not affected by food supplementation or litter size manipulation. As we have previously shown elsewhere, extra food increases the reproductive success of bank vole females in terms of size and proportion of weaned offspring. According to the present data, greater overlap of female home ranges had a negative effect on reproductive success of females, particularly on survival of offspring. We conclude that higher food availability increases the reproductive success of bank vole females, and this effect may be mediated through lower vulnerability of offspring to direct killing and/or detrimental effects from other females in the population. Moreover, it seems that when density of conspecifics is controlled for, home range sizes of females, but not territoriality, is related to food resources in Clethrionomys voles.     

Sexual differences in spatio-temporal interaction among badgers

I tested the following hypotheses of territorial polygyny on badgers (Taxidea taxus: Carnivora; Mustelidae): Competition among adult females for food should result in intrasexual territoriality, while male competition for females should result in larger territories that encompass multiple female territories. The sagebrush-grassland study area (Wyoming, USA) contained a depauperate terrestrial fauna with a dense badger population preying on high densities of ground squirrels (Spermophilus armatus). Implant telemetry generated locations for analysis of home range and spatio-temporal interaction. During the summer breeding season males doubled movement rates and nearly tripled home range areas to overlap those of females. Before and after the breeding season, males reduced their home ranges to sizes nearer those of stable female ranges ( =2.82 km²). Unexpectedly, home range overlap between males and females was no different than intrasexual overlap. However, analysis of spatio-temporal interaction revealed that females spatially avoided one another, while males were spatially and temporally attacted to one another, similar to that of male-female interactions. Presumably, olfactory mechanisms allow resource tracking and lagged communication. Male-male territoriality was not viable, most likely because the high density of badgers, combined with the severely male-biased sex ratio (1.75:1), effectively increased intruder pressure — as a resource, receptive females were too mobile and spatially unpredictable within their home ranges. Consequently, males monitored and searched widely for relatively scarce females during the breeding season with the effect of attracting each other. Male mobility, home range size, and possibly aggression increased with age, suggesting age-related breeding tactics, although dominance could only be surmised. This and other studies suggest how the spatial, temporal, and dominance components of carnivore resource partitioning and sociality will be understood better by unraveling the interplay of olfactory processes, attributes of disparate resources (e.g., food vs. females), seasonality, and population density and age-sex structure.     

Resource distribution influences mating system in the bobuck (<Emphasis Type="Italic">Trichosurus cunninghami</Emphasis>: Marsupialia)

Mammalian mating systems are thought to be shaped by the spatial distribution and abundance of key resources, which in turn influence the spacing behaviour of individuals. In particular, female home range size is predicted to reflect the availability of key resources. We documented the availability and distribution of food and shelter resources for two neighbouring populations of bobucks, or mountain brushtail possums, Trichosurus cunninghami, that were characterised by different mating systems: our “forest population” was socially monogamous, whereas the “roadside population” was polygynous. Both silver wattle, Acacia dealbata, the main food resource for bobucks, and den-trees, which provided shelter, occurred at significantly higher density at the roadside site. The pattern of distribution of these two resources also differed between the sites. Both food and den-trees were scattered evenly throughout the roadside habitat. In contrast, den-trees were located predominantly at one end of the forest site, while silver wattle trees were located at the other. There was no significant difference in the amount of silver wattle, or in the number of den-trees, located within the home ranges of individual females at the two sites. However, forest females had home ranges, on average, almost three times the size of those of roadside females. At the roadside site, the size of female home ranges varied inversely with the density of silver wattle, indicating that these females ranged over as large an area as necessary to gain access to sufficient silver wattle trees. There was no such relationship among forest females. These populations provide a clear example of resource distribution determining female home range size. This influenced the number of female home ranges a male’s home range overlapped with, which in turn determined the mating system. Such clear links between resource availability and mating system have not previously been established in a marsupial.     

The mating system of the White-throated Magpie-jay Calocitta formosa and Greenwood's hypothesis for sex-biased dispersal

Greenwood explained the different sex bias in dispersal of birds (usually female biased) and mammals (usually male biased) by a difference in mating systems: male birds primarily defend resources while male mammals primarily defend females. The White-throated Magpie-jay Calocitta formosa is unusual among birds in that females are philopatric and jointly defend permanent resource territories while males disperse before they are 2 years of age. One female in a group is the primary breeder. One male joins the group permanently as her mate. Males that do not have a permanent breeding position circulate among groups and attempt to mate with both the primary breeding female and other group females. Other females feed the primary breeder and her offspring and also pursue other reproductive behaviour, including secondary nesting in the territory and egg dumping into the primary breeder's nest. I argue that the unusual dispersal pattern in this species is a result of the alternative reproductive strategies that can be pursued by males and females excluded from being primary breeders. The White-throated Magpie-jay conforms to Greenwood's predictions: males pursue a mate defence rather than resource defence mating system and they are the dispersing sex. The primary factor influencing alternative reproductive tactics may be asynchronous reproduction among groups during the long breeding season arising from frequent renesting in an area of high nest predation.     

Why do male chimpanzees defend a group range?

Male chimpanzees, Pan troglodytes, cooperate to defend a community range within which resident females range in smaller core areas. There has been debate over exactly what males are defending, whether mates, territory or both. One hypothesis holds that males are defending mates, and that an increase in community range size will lead directly to the acquisition of more females. However, males frequently attack females as well as males at the edge of the community range. We examined 18 years of observational data on the Gombe chimpanzees to determine the behaviour of males during extragroup encounters, and the consequences of changes in community range size on the number of adult females and indirect measures of food availability. Males were always aggressive to males from other communities, and often attacked adult females, especially those that were not sexually receptive, were older, and/or had more than one offspring. The number of females did not increase with range size, but several measures suggested an increase in food availability with range size. These measures include more time spent in large foraging parties, higher encounter rates with resident females, more encounters with sexually receptive females and higher female reproductive rates. These findings suggest that males defend a feeding territory for their resident females and protect them from sexual harassment. Although a large range may eventually attract more females, this is not an immediate consequence of range expansion. Male number was not correlated with community range size.     

Resource heterogeneity influences home range area in the swamp wallaby Wallabia bicolor

Home range area is influenced by the spatio‐temporal distribution of multiple resources, but current theoretical frameworks such as the habitat productivity and resource dispersion hypotheses fail to account for this adequately. We propose a conceptual framework for quantifying the influence of multiple resources on home range area where separate resources interact to form a continuous, multi‐dimensional resource surface exhibiting an emergent environmental pattern. We adopt the term resource heterogeneity to describe this pattern, and predict that home range area will be more closely correlated with resource heterogeneity than with simple additive or interactive effects of separate resources. Initially, we quantified resource heterogeneity as the geometric mean of resource abundance, and tested the performance of this index against simulated low, moderate and high heterogeneity scenarios. In all cases, the geometric mean reflected the modelled scenarios well, demonstrating its utility as a heterogeneity index. We then quantified shelter and food resources within the home ranges of swamp wallabies Wallabia bicolor, and used these data in a generalised linear mixed modelling framework to test our prediction. Based on Akaike's information criterion (AIC_c), the best model included the main effect of sex and the heterogeneity index. Although model selection uncertainty was relatively high (largest Akaike weight=0.37), the AIC_c value associated with the best model was 2.41 units less than the highest ranked model including shelter and food, indicating support for our prediction. Home range area was negatively correlated with resource heterogeneity, and males had larger home ranges than females (37.6 (28.5, 49.7) ha compared to 17.2 (13.6, 21.7) ha; mean and 95% CLs). We suggest that statistical models of home range area parameterised using an index of resource heterogeneity will often be superior to those that focus on a single resource, or fail to take the heterogeneity of multiple resources into account.     

Environmental determinants of butterflyfish social systems

Synopsis Butterflyfishes (Chaetodontidae) display a variety of social systems, including monogamous pair-bonds, harems, and schooling with group spawning. The range of reproductive options available to butterflyfishes is shaped by their general life history characteristics, such as broadcast spawning with widely dispersed pelagic larvae, large body size and low adult mortality. The distribution and quality of food resources are major determinants of group size and mobility, thereby influencing the relative costs and benefits of available options, and determining specific social systems. Planktivorous and corallivorous butterflyfishes exemplify the relationship between food resources and social systems. Pelagic plankton is a patchy, but temporally and spatially unpredictable food resource which is efficiently exploited by fish in mobile schools. Neither sex is able to monopolize food resources necessary for the other sex, and plantivorous butterflyfishes appear constrained to spawn in groups. In contrast, corals are stable and predictable in space and time, favoring residence in one area and territorial defense of that space by coral-feeding butterflyfishes. Females defend food resources from other females, and males defend territories containing a female from other males. Males attempt to defend areas containing more than one female, but are unsuccessful. A monogamous social system results. This system favors the evolution of cooperative behavior between mates to increase female fecundity, as long as the male has an opportunity of sharing in that reproduction. Mate removal experiments conducted on two monogamous coral-feeding species,Chaetodon multicinctus andChaetodon quadrimaculatus reveal a division of labor between male and female pair-mates. Paired males assume most of the territorial defense activities, allowing their mates to feed more.     

Mating system structure and population density in a polygynous lizard, Sauromalus obesus (= ater)

Increases in population density often are associated with achange in mating system structure in numerous taxa. Typically,male interactions are minimal in extremely low density populations.As density increases, males exhibit territoriality but if densitybecomes too high, the energetic cost of defending a territorywill eventually outweigh the reproductive benefits associatedwith territoriality. Consequently, males in high density populationsmay abandon territoriality and adopt dominance polygyny, lekking behavior, or scramble competition. We investigated the relationshipbetween population density and mating system structure in threepopulations of the chuckwalla, Sauromalus obesus (= ater),near Phoenix, Arizona. Densities in the Phoenix Mountains (2.7chuckwallas/ha) were lower than any population previously studied.In the Santan Mountains (10.9 chuckwallas/ha), densities weresimilar to populations studied in the Mojave Desert, and inthe South Mountains (65 chuckwallas/ha), densities were the highest yet recorded. Male mating behavior was examined by determininghome range overlap and by making direct behavioral observations.Male home range size decreased with increasing population density.There was little overlap in home ranges among males in allthree populations, whereas home ranges of males and femalesconsistently overlapped, indicating that males were strictly territorial. This conclusion was supported by behavioral observationsof interactions among individuals in a natural setting. Thenumber of females wihin male territories was correlated withfood resources (plants) in all three populations. Female homerange size appeard to be related to food resources whereasmale home ranges appeared to be related to female distribution,population density, and geology. The retention of territoriality in spite of high population densities raises new questions aboutthe relationship between density and resource defense.     

Territoriality in Lake Eyre Dragons Ctenophorus maculosus: are Males ‘Superterritorial’?

The Australian Lake Eyre dragon, Ctenophorus maculosus, lives on dry salt lakes in the Australian interior. An unusual characteristic of this habitat is that windblown insects are the major food resource, which makes it impossible for males to defend site-related resources. Male territory size is not correlated to male size; thus, males do not seem to defend trophic territories in relation to their own energy demands. Instead, males with higher densities of lookout sites have larger territories, and males with larger territories have more mates. In consequence, males primarily seem to guard sexual resources on territories that are not economically defensible from a trophic point of view; males appear to conform to the concept of ‘superterritoriality’ (sensu Stamps 1983).     

Phenotypic and genetic integration of personality and growth under competition in the sheepshead swordtail,Xiphophorus birchmanni

Competition for resources including food, physical space, and potential mates is a fundamental ecological process shaping variation in individual phenotype and fitness. The evolution of competitive ability, in particular social dominance, depends on genetic (co)variation among traits causal (e.g., behavior) or consequent (e.g., growth) to competitive outcomes. If dominance is heritable, it will generate both direct and indirect genetic effects (IGE) on resource‐dependent traits. The latter are expected to impose evolutionary constraint because winners necessarily gain resources at the expense of losers. We varied competition in a population of sheepshead swordtails, Xiphophorus birchmanni, to investigate effects on behavior, size, growth, and survival. We then applied quantitative genetic analyses to determine (i) whether competition leads to phenotypic and/or genetic integration of behavior with life history and (ii) the potential for IGE to constrain life history evolution. Size, growth, and survival were reduced at high competition. Male dominance was repeatable and dominant individuals show higher growth and survival. Additive genetic contributions to phenotypic covariance were significant, with the G matrix largely recapitulating phenotypic relationships. Social dominance has a low but significant heritability and is strongly genetically correlated with size and growth. Assuming causal dependence of growth on dominance, hidden IGE will therefore reduce evolutionary potential.     

Spacing Behavior of a Non‐Larder‐Hoarding Tamiasciurus: A Study of Mearns's Squirrels in Xeric Coniferous Forests

In ecosystems with seasonal fluctuations in food supply many species use two strategies to store food: larder hoarding and scatter hoarding. However, because species at different geographic locations may experience distinct environmental conditions, differences in hoarding behavior may occur. Tree squirrels in the genus Tamiasciurus display variation in hoarding behavior. Whereas red (Tamiasciurus hudsonicus) and Douglas's (Tamiasciurus douglasii) squirrels in mesic coniferous forests defend territories centered around larder hoards maintaining non‐overlapping home ranges, red squirrels in deciduous forests defend small scatter‐hoarded caches of cones maintaining overlapping home ranges. As in other rodent species, variation in hoarding behavior appears to influence the spacing behavior of red and Douglas's squirrels. In contrast, Mearns's squirrels (Tamiasciurus mearnsi) in xeric coniferous forests neither rely on larder hoards nor appear to display territorial behavior. Unfortunately, little is known about the ecology of this southernmost Tamiasciurus. Using radiotelemetry, we estimated home‐range size, overlap, and maximum distance traveled from nest to examine the spacing behavior of Mearns's squirrels. Similar to scatter‐hoarding rodents, maximum distance traveled from nest was greater for males during mating season, whereas those of females were similar year round. Although no seasonal differences were detected, male home ranges were three times larger during mating season, whereas those of females were smaller and displayed a minor variation between seasons. Home ranges were overlapped year round but contrary to our expectations, overlap was greater during mating season for both sexes, with no detectable relationship between male home‐range size and the number of females overlapped during mating season. Overall, the results appear to support our hypothesis that in the absence of larder hoards, the spacing behavior of Mearns's squirrels should be different from larder‐hoarding congeners and more similar to scatter‐hoarding rodents.     

Spatial distributions of male and female strawberry poison frogs and their relation to female reproductive resources

In many species with a resource-based mating system, males defend resources to increase their attractiveness to females. In the strawberry poison frog, Dendrobates pumilio, suitable tadpole-rearing sites appear to be a limited resource for females. Territorial males have been suggested to defend tadpole-rearing sites to increase their access to females. In this study we investigate the spatial association between tadpole-rearing sites and the sexes as well as the spatial association of males and females. If strawberry poison frogs have resource defense polygyny, we expect males and females to be associated with tadpole-rearing sites and that females will deposit their offspring in tadpole-rearing sites inside the territories of their mates. To test this hypothesis, home range and core area sizes were calculated for both sexes and the association patterns were compared in two areas that differed in their abundance of tadpole-rearing sites. Home ranges and core areas of females were much larger than male home ranges. Females showed a clumped distribution in the vicinity of tadpole-rearing sites. Males were not clumped and were less associated with tadpole-rearing sites. Females generally did not use tadpole-rearing sites in the territory of their mates and we therefore conclude that males did not defend tadpole-rearing sites for females. Our data are consistent with the general assumption that female distribution is influenced by resource distribution and that male distribution depends on female distribution. Nevertheless, the distribution of D. pumilio females was also influenced by male spacing patterns. Males probably initially establish their core areas where female density is high and then females move among territories to sample males. Males compete vigorously for places with high female density, the defense of which is likely important for enhancing their mating success. In general, the spacing patterns did not differ between populations but the sex ratio was strongly female biased in the habitat with more tadpole-rearing sites, reflecting the direct reliance of females on these resources.     

The Causes of Resource Monopolization: Interaction Between Resource Dispersion and Mode of Competition

The degree of monopolization of resources is thought to be higher in groups that compete by interference than by exploitation. However, the monopolization of resources will presumably depend on (1) whether the dispersion of resources is economically defendable, and (2) whether some competitors have the ability to defend these resource distributions and hence capitalize on this potential. We tested for an interaction between the effects of temporal resource dispersion and aggressiveness on the degree of resource monopolization in a foraging system. Two species of fish differing markedly in aggressiveness (high: convict cichlids, Archocentrus nigrofasciatus; low: goldfish, Carrasius auratus) were allowed to compete intra‐specifically in groups of four for food that was either potentially defendable (arrived asynchronously) or not (arrived synchronously). As predicted, the monopolization of food, measured as the coefficient of variation of food eaten within groups, was significantly higher in the defendable than in the undefendable treatment for convict cichlids but not for goldfish. However, the monopolization of food was higher in the non‐aggressive goldfish than in the aggressive convict cichlids. Future studies should quantify and compare the monopolization in species that compete primarily via scramble competition to those that use primarily resource defence.     

Ranging Movements of Female Roe Deer: Do Home-loving Does Roam to Mate?

Bimonthly changes in home range size of seven mature roe deer Capreolus capreolus L. females were analysed over one year. Great stability of home range size and high site fidelity was common to all females, which remained bimonthly within areas of 6.1–20.8 ha. Two groups of females could be identified on the basis of bimonthly variations in their home range sizes: females with larger areas (LHR females), who decreased their ranges in the birth season only, and females with smaller home ranges (SHR females), who increased significantly their home ranges during the rut. The most likely explanation is that the areas inhabited by SHR females included high-quality food resources allowing survival even in small home ranges. In the rut, SHR females may have expanded their ranges to increase mating opportunities.     

Social Monogamy in the Big-Clawed Snapping Shrimp, Alpheus heterochelis

Social monogamy has evolved independently in many taxa, and often involves biparental care of the young. Where it does not, mate guarding and shared territoriality have been invoked as causal factors. We evaluated mate guarding and shared resource defence (a common shelter) as factors that could have led to social monogamy in the snapping shrimp, Alpheus heterochelis. This species is found in male–female pairs that defend a common shelter together. Female receptivity lasts only for a few hours immediately after her periodic moult. Their monogamous pair bond may represent mate guarding or joint defence of a territory. Monogamy in A. heterochelis seems most importantly driven by the cryptic nature of the female's moult cycle. We found that males did not discriminate among females at different intermoult stages for pairing, nor did they modulate their defence of mate and shelter (vs. the risk in finding a new shelter and mate) according to female moult stage. This, together with the short period of female receptivity before her single copulation per cycle, make extended mate guarding the most efficient method for a male to secure a mating opportunity. Comparing eviction rates of paired and unpaired shelter residents by conspecific intruders provided no evidence of enhanced resource defence that would confer a selective advantage to a pair. Male presence during the moult is beneficial for the female, as searching for a male during her soft-bodied receptive phase would put her at mortal risk. Our results show empirically for the first time that guarding may be beneficial, even if males are not able to assess the female's reproductive stage. This extends the theoretical framework for understanding the evolution of social monogamy in taxa without biparental care of young.