Anne W. Goldizen

Saddle-back tamarin (Saguinus fuscicollis) reproductive strategies : evidence from a thirteen-year study of a marked population

We monitored a population of four to seven groups of individually marked saddle‐back tamarins (Saguinus fuscicollis; Callitrichidae) at the Cocha Cashu Biological Station in Perus Manu National Park every year from 1979 through 1992. In this paper we use data on life histories, group compositions, group formations, and dispersal patterns collected during these 13 years to examine the reproductive strategies of males and females. Group compositions and mating patterns were quite variable in this population, with both monogamy and cooperative polyandry common. In polyandrous groups, two males shared a females copulations and cooperatively cared for her young. Although most groups contained a single breeding female, we recorded four cases in which secondary females successfully reared young. Most young females appeared to wait in their natal groups for the first opportunity to fill a primary breeding position in their own or a neighboring group. Females that acquired primary breeding positions maintained those positions for a mean of 3 years. No female was observed to transfer between groups a second time. Variation in female lifetime reproductive success was high. Half of the females marked as juveniles never bred; the other half produced an average of 3.5 young. A paucity of female breeding opportunities may explain the high mortality of females between 2.5 and 4.5 years of age and the resulting male‐biased adult sex ratio. The majority of groups contained more than one probable male breeder. Polyandrous groups included both related and unrelated males. Behavioral differences between Cocha Cashu tamarins and other studied populations may result from the pressures of living in an environment inhabited by nine other primate species and numerous predators.

SEASONAL FOOD SHORTAGE, WEIGHT-LOSS, AND THE TIMING OF BIRTHS IN SADDLE-BACK TAMARINS (SAGUINUS-FUSCICOLLIS)

SUMMARY (1) Annual birth peaks in the breeding of several primate species are thought to correlate with seasonal changes in food availability, yet no study published to date has both correlated birth seasonality with food availability, and shown that the physical conditions of individuals decline during annual periods of food scarcity. (2) We document the following observations in a population of saddle-back tamarins (Saguinusfuscicollis Spix; Callitrichidae) at the Cocha Cashu Biological Station in Perus Manu National Park. (3) The availability of both fruits and insects was substantially lower during the annual 4-month dry season (May-September) than at other times of the year. (4) Individual tamarins lost an average of 5% of their weight over this period. (5) Three-quarters of twenty-two S. fuscicollis births at this site occurred between November and February, and none occurred between mid-March and mid-August. (6) We suggest that tamarin births at Cocha Cashu are timed such that lactation and weaning occur when food is abundant, because during the period of low food availability, there would be insufficient food to meet the demands of lactation and to serve as easily obtainable weaning foods. In this sort of seasonal environment, tamarins appear to be constrained, by the seasonality of their food supply, from breeding as frequently as they do in captivity.

A landscape genetics approach for quantifying the relative influence of historic and contemporary habitat heterogeneity on the genetic connectivity of a rainforest bird.

Landscape genetics is an important framework for investigating the influence of spatial pattern on ecological process. Nevertheless, the standard analytic frameworks in landscape genetics have difficulty evaluating hypotheses about spatial processes in dynamic landscapes. We use a predictive hypothesis‐driven approach to quantify the relative contribution of historic and contemporary processes to genetic connectivity. By confronting genetic data with models of historic and contemporary landscapes, we identify dispersal processes operating in naturally heterogeneous and human‐altered systems. We demonstrate the approach using a case study of microsatellite polymorphism and indirect estimates of gene flow for a rainforest bird, the logrunner (Orthonyx temminckii). Of particular interest was how much information in the genetic data was attributable to processes occurring in the reconstructed historic landscape and contemporary human‐modified landscape. A linear mixed model was used to estimate appropriate sampling variance from nonindependent data and information‐theoretic model selection provided strength of evidence for alternative hypotheses. The contemporary landscape explained slightly more information in the genetic differentiation data than the historic landscape, and there was considerable evidence for a temporal shift in dispersal pattern. In contrast, migration rates estimated from genealogical information were primarily influenced by contemporary landscape change. We discovered that landscape heterogeneity facilitated gene flow before European settlement, but contemporary deforestation is rapidly becoming the most important barrier to logrunner dispersal.

Fine‐scale spatial genetic correlation analyses reveal strong female philopatry within a brush‐tailed rock‐wallaby colony in southeast Queensland

We combine spatial data on home ranges of individuals and microsatellite markers to examine patterns of fine‐scale spatial genetic structure and dispersal within a brush‐tailed rock‐wallaby (Petrogale penicillata) colony at Hurdle Creek Valley, Queensland. Brush‐tailed rock‐wallabies were once abundant and widespread throughout the rocky terrain of southeastern Australia; however, populations are nearly extinct in the south of their range and in decline elsewhere. We use pairwise relatedness measures and a recent multilocus spatial autocorrelation analysis to test the hypotheses that in this species, within‐colony dispersal is male‐biased and that female philopatry results in spatial clusters of related females within the colony. We provide clear evidence for strong female philopatry and male‐biased dispersal within this rock‐wallaby colony. There was a strong, significant negative correlation between pairwise relatedness and geographical distance of individual females along only 800 m of cliff line. Spatial genetic autocorrelation analyses showed significant positive correlation for females in close proximity to each other and revealed a genetic neighbourhood size of only 600 m for females. Our study is the first to report on the fine‐scale spatial genetic structure within a rock‐wallaby colony and we provide the first robust evidence for strong female philopatry and spatial clustering of related females within this taxon. We discuss the ecological and conservation implications of our findings for rock‐wallabies, as well as the importance of fine‐scale spatial genetic patterns in studies of dispersal behaviour.

Songs of male humpback whales, Megaptera novaeangliae, are involved in intersexual interactions

Male humpback whales produce complex songs during the breeding season, yet the singing behaviour of males and whether songs function in male contests and/or through female choice are still poorly understood. We investigated song function by obtaining simultaneous observations of the positions and movements of singing and nonsinging whales in real time during their migration off the east coast of Australia. We collected movement data by acoustic tracking using a hydrophone array, land-based visual tracking and observations from a small boat. Of the 114 singers analysed, 66 (58%) associated with conspecifics. Singers were significantly more likely to join groups containing a mother–calf pair than other groups. Males started to sing after joining groups only if they consisted of a mother–calf pair not escorted by another male. Singers also associated longer and sang for a significantly greater proportion of time with mother–calf pairs than any other group type. Associating with mother–calf pairs has been shown to be a reproductively successful strategy for males. In contrast, whales that joined singers were usually lone males; these associations were brief and singers typically stopped singing in the presence of other males. This is the highest reported incidence in humpback whales of males singing when escorting females and supports an intersexual function of song in humpback whales. We suggest that males joining singers are prospecting for females rather than engaging in male social ordering and that singing may incur the cost of attracting competing males.

Interactions among social monitoring, anti-predator vigilance and group size in eastern grey kangaroos

Group size is known to affect both the amount of time that prey animals spend in vigilance and the degree to which the vigilance of group members is synchronized. However, the variation in group-size effects reported in the literature is not yet understood. Prey animals exhibit vigilance both to protect themselves against predators and to monitor other group members, and both forms of vigilance presumably influence group-size effects on vigilance. However, our understanding of the patterns of individual investment underlying the time sharing between anti-predator and social vigilance is still limited. We studied patterns of variation in individual vigilance and the synchronization of vigilance with group size in a wild population of eastern grey kangaroos (Macropus giganteus) subject to predation, in particular focusing on peripheral females because we expected that they would exhibit both social and anti-predator vigilance. There was no global effect of group size on individual vigilance. The lack of group-size effect was the result of two compensating effects. The proportion of time individuals spent looking at other group members increased, whereas the proportion of time they spent scanning the environment decreased with group size; as a result, overall vigilance levels did not change with group size. Moreover, a degree of synchrony of vigilance occurred within groups and that degree increased with the proportion of vigilance time peripheral females spent in anti-predator vigilance. Our results highlight the crucial roles of both social and anti-predator components of vigilance in the understanding of the relationship between group size and vigilance, as well as in the synchronization of vigilance among group members.

GENETIC POPULATION STRUCTURE AND CALL VARIATION IN A PASSERINE BIRD, THE SATIN BOWERBIRD, PTILONORHYNCHUS VIOLACEUS

Abstract Geographic variation in vocalizations is widespread in passerine birds, but its origins and maintenance remain unclear. One hypothesis to explain this variation is that it is associated with geographic isolation among populations and therefore should follow a vicariant pattern similar to that typically found in neutral genetic markers. Alternatively, if environmental selection strongly influences vocalizations, then genetic divergence and vocal divergence may be disassociated. This study compared genetic divergence derived from 11 microsatellite markers with a metric of phenotypic divergence derived from male bower advertisement calls. Data were obtained from 16 populations throughout the entire distribution of the satin bowerbird, an Australian wet‐forest‐restricted passerine. There was no relationship between call divergence and genetic divergence, similar to most other studies on birds with learned vocalizations. Genetic divergence followed a vicariant model of evolution, with the differentiation of isolated populations and isolation‐by‐distance among continuous populations. Previous work on Ptilonorhynchus violaceus has shown that advertisement call structure is strongly influenced by the acoustic environment of different habitats. Divergence in vocalizations among genetically related populations in different habitats indicates that satin bowerbirds match their vocalizations to the environment in which they live, despite the homogenizing influence of gene flow. In combination with convergence of vocalizations among genetically divergent populations occurring in the same habitat, this shows the overriding importance that habitat‐related selection can have on the establishment and maintenance of variation in vocalizations.

The importance of functional connectivity in the conservation of a ground-dwelling mammal in an urban Australian landscape

The distribution of the northern brown bandicoot (Isoodon macrourus), a medium-sized ground-dwelling marsupial, was examined in habitat fragments within the urban landscape of the city of Brisbane, Australia. From surveys conducted in 68 fragments, bandicoots were found to be present in 33 (49%) despite widespread habitat loss and fragmentation. Logistic regression analysis revealed that of 13 measured independent variables, functional connectivity was the only factor that significantly predicted the presence of bandicoots within fragments, with connectivity positively correlated with the likelihood of occupation. Functional connectivity was equated to the likelihood of bandicoot immigration into the focal fragment from the nearest occupied fragment, based on the estimated resistance to movement offered by the intervening matrix. Within Brisbane, riparian habitat fragments typically have a relatively high level of functional connectivity, as thin strips of vegetation fringing waterways serve as corridors between larger riparian areas and facilitate the movement of bandicoots between patches. Analyses based on the Akaike Information Criterion revealed that the optimal model based on landscape context variables was convincingly better supported by the data than the optimal model produced from fragment characteristics. However, it is important to examine both internal attributes of habitat fragments and external features of the surrounding landscape when modelling the distribution of ground-dwelling fauna in urban environments, or other landscapes with a highly variable matrix. As urban centres throughout the world expand, it is crucial that the ecology of local wildlife be considered to ensure functional connection is maintained between habitat patches, especially for the conservation of species that are highly susceptible to fragmentation.

Demography and Dispersal Patterns of a Tamarin Population: Possible Causes of Delayed Breeding

We analyze the demography and dispersal patterns of a population of wild saddle-back tamarins (Saguinus fuscicollis) in Peru. Saddle-back tamarins live in small groups with one reproductive female and one or two breeding males. Data on the ages at which females had their first young and the ages at which males and females emigrated from their natal territories show that most animals do not first breed for at least one year past the age of potential sexual maturity. Data on the survival of adults and the lengths of tenure of breeders suggest that breeding vacancies are not frequent. Emigration and survival patterns are not significantly different for the two sexes. We suggest that delayed first breeding may occur in this species for any or all of the following reasons: a shortage of breeding positions, territories, or helpers; the risks of solitary dispersal; and the inclusive-fitness benefits gained from helping. We compare the demographic patterns of S. fuscicollis with those of well-studied cooperatively breeding species and suggest that two preconditions of helping behavior, high costs of infant care and frequent delayed breeding, are quite similar in cooperatively breeding birds and tamarins.

Long-term effects of the cleaner fish Labroides dimidiatus on coral reef fish communities.

Cleaning behaviour is deemed a mutualism, however the benefit of cleaning interactions to client individuals is unknown. Furthermore, mechanisms that may shift fish community structure in the presence of cleaning organisms are unclear. Here we show that on patch reefs (61–285 m2) which had all cleaner wrasse Labroides dimidiatus (Labridae) experimentally removed (1–5 adults reef−1) and which were then maintained cleaner-fish free over 8.5 years, individuals of two site-attached (resident) client damselfishes (Pomacentridae) were smaller compared to those on control reefs. Furthermore, resident fishes were 37% less abundant and 23% less species rich per reef, compared to control reefs. Such changes in site-attached fish may reflect lower fish growth rates and/or survivorship. Additionally, juveniles of visitors (fish likely to move between reefs) were 65% less abundant on removal reefs suggesting cleaners may also affect recruitment. This may, in part, explain the 23% lower abundance and 33% lower species richness of visitor fishes, and 66% lower abundance of visitor herbivores (Acanthuridae) on removal reefs that we also observed. This is the first study to demonstrate a benefit of cleaning behaviour to client individuals, in the form of increased size, and to elucidate potential mechanisms leading to community-wide effects on the fish population. Many of the fish groups affected may also indirectly affect other reef organisms, thus further impacting the reef community. The large-scale effect of the presence of the relatively small and uncommon fish, Labroides dimidiadus, on other fishes is unparalleled on coral reefs.