Behaviour

Luque, Sebastián; Guinet, Christophe

doi: 10.1163/156853907782418213pmid: N/A

AbstractForaging behaviour frequently occurs in bouts, and considerable efforts to properly define those bouts have been made because they partly reflect different scales of environmental variation. Methods traditionally used to identify such bouts are diverse, include some level of subjectivity, and their accuracy and precision is rarely compared. Therefore, the applicability of a maximum likelihood estimation method (MLM) for identifying dive bouts was investigated and compared with a recently proposed sequential differences analysis (SDA). Using real data on interdive durations from Antarctic fur seals (Arctocephalus gazella Peters, 1875), the MLM-based model produced briefer bout ending criterion (BEC) and more precise parameter estimates than the SDA approach. The MLM-based model was also in better agreement with real data, as it predicted the cumulative frequency of differences in interdive duration more accurately. Using both methods on simulated data showed that the MLM-based approach produced less biased estimates of the given model parameters than the SDA approach. Different choices of histogram bin widths involved in SDA had a systematic effect on the estimated BEC, such that larger bin widths resulted in longer BECs. These results suggest that using the MLM-based procedure with the sequential differences in interdive durations, and possibly other dive characteristics, may be an accurate, precise, and objective tool for identifying dive bouts.

Buckingham, Jessica; Wong, Bob; Rosenthal, Gil

doi: 10.1163/156853907782418196pmid: N/A

AbstractLittle is known about the mechanisms individuals might use to compare group sizes when making decisions about group membership. One possibility is that animals use ratio to determine differences in group sizes. Weber's Law states that the ease of any numerical comparison is based on the ratio between the stimuli compared; as the ratio becomes smaller the comparison becomes more difficult. We set out to test this prediction by offering female green swordtails, Xiphophorus helleri, dichotomous choices between different shoal sizes, varying both in ratios and absolute numbers of fish. Swordtails attended to the ratio of group size between stimulus shoals, rather than the numerical difference between shoals, when making shoaling decisions. Where group size ratio was 2:1, subjects showed a significant preference for the larger shoal, independent of the numerical difference between the shoals. When the ratio was 1.5:1, subjects showed no preference. The ratio between group sizes may, thus, be an important factor in shoaling decisions. More broadly, ratio could prove to be a widespread mechanism for animals to make numerical comparisons in group assessments.

Webster, ; Atton, ; Ward, ; Hart,

doi: 10.1163/156853907782418222pmid: N/A

AbstractIn aquatic habitats turbidity can affect the foraging efficiency of visual predators, directly influencing their capacity to detect prey. In a laboratory study we tested the effect of different loads of suspended sediment upon the foraging rates of threespine sticklebacks (Gasterosteus aculeatus). We compared the foraging rates of fish under a series of different turbidity treatments, testing fish originating from four habitats within a single drainage basin that differed in a number of environmental parameters including turbidity. Although we found habitat specific differences in foraging rates, these did not correspond to local turbidity levels. The findings of a follow up experiment revealed habitat-specific variation in boldness, which may be indirecly linked to the observed differences in foraging rate. The main finding of our study was that turbidity alone had no impact upon their prey capture rates, but that high turbidity in combination with saturation with prey odour extract caused prey capture rates to fall significantly. This suggests that olfactory cues can be more important than visual cues in determining foraging performance in this species, potentially influencing how they cope with naturally occurring periods of turbidity, and how they adapt to human-induced eutrophication.

Verdolin,

doi: 10.1163/156853907782418231pmid: N/A

AbstractPrevious studies of Gunnison's prairie dogs, Cynomys gunnisoni, have reached different conclusions about the factors influencing sociality in this species. In this study I tested whether Gunnison's prairie dog social structure was resource-based or whether male mating strategies drive the organizational patterns observed. Group size, where the term group refers to individuals occupying the same territory, was predicted by territory size and density of food available. The spatial overlap of adults within territories was positively correlated with spatial patchiness of food resources. All group members participated in territory defense, although adult males engaged in significantly more intergroup aggressive interactions. There was no significant difference in adult male and female home range size. The number of female home ranges that any given male home range overlapped was not correlated with male body mass, male home range size, or territory size. Contrary to predictions of typical mammalian male mating strategies, adult females ranged significantly further than males during the mating period. Body mass of males and nonreproductive females was similar, whereas that of reproductive females was smaller. In addition, males and females did not differ in size, based on skull length and skull width. Results from this study strongly suggest that patterns of space use and social structure in Gunnison's prairie dogs are the result of individual responses to resource abundance and distribution and are not due to male mating strategies, such as resource defense or female defense polygyny.

Zaldívar-Rae, Jaime; Drummond, Hugh

doi: 10.1163/156853907782418187pmid: N/A

AbstractPost-copulatory female accompaniment by males is often interpreted as mate guarding. However, several alternative hypotheses for the function of accompaniment have received little attention. We analysed potential functions of post-copulatory accompaniment in whiptail lizards, Aspidoscelis costata, by comparing 23 accompanied females and 54 unaccompanied females in the field. Male companions closely followed females for 1 to 2 days around ovulation, after which females became unreceptive. Unaccompanied females were in all stages of the reproductive cycle, including 12 nearly-ovulating females. Male companions were aggressive to other males and, on average, won 98.7% of interactions. Only pairs in accompaniment performed consensual copulations (1 to 3 per pair). Solitary males attempted opportunistic copulations but did not selectively target nearly-ovulating females. Male companions attacked rivals attempting opportunistic copulations, but did not copulate in retaliation when attempts were successful. Accompaniment reduced lunges and pursuits from other males on females, but did not reduce opportunistic copulations or predation, or increase foraging opportunities for females. Through accompaniment, males likely (1) copulate repeatedly, (2) swamp rival sperm, (3) inseminate females more and (4) monopolise access to fertile females, whereas females may receive (1) post-copulatory courtship, (2) copulations with high quality males and (3) sufficient sperm for fertilisation.

Przybylski, Mirosław; Reichard, Martin; Spence, Rowena; Smith, Carl

doi: 10.1163/156853907782418204pmid: N/A

AbstractWe investigated reproductive rate in relation to oviposition site distribution and quality in the European bitterling, Rhodeus amarus, a freshwater fish that spawns on the gills of living unionid mussels. In a laboratory experiment male bitterling led females to groups of four mussels at a significantly higher rate than single mussels, irrespective of mussel species. Females spawned significantly more frequently on the gills of mussels in groups than on solitary mussels, and showed a preference for spawning on the gills of Unio pictorum in comparison with Anodonta anatina. In a field experiment the total number of eggs spawned on the gills of four mussels was significantly higher than that of single mussels, though the mean number of eggs per mussel was equivalent within species. There was a significant effect of species on the number of eggs spawned in mussels; U. pictorum and U. tumidus received more eggs than A. anatina and A. cygnea. We discuss these results in the context of mating system evolution.

Martin, Jennifer; Handasyde, Kathrine; Taylor, Andrea; Coulson, Graeme

doi: 10.1163/156853907782418240pmid: N/A

AbstractMost mammals are polygynous and are characterised by male-biased sexual size dimorphism. One hallmark of mammalian monogamy is the lack of such dimorphism. Bobucks, or mountain brushtail possums, Trichosurus cunninghami, lack sexual size dimorphism; however, few behavioural data exist for this species. We studied the mating system of a bobuck population in south-eastern Australia. Adult bobucks were strongly paired: pair-members had exclusive access to a suite of den-trees and overlapped in home range on average by 70%. Pair-members rested together in the same tree-hollow on approximately 70% of days during the breeding season and 47% of days during the non-breeding season. While active, pair-members remained within approximately 8 m of one another during the breeding season and within 31 m of one another during the non-breeding season. Females established pair-bonds at 2-5 years of age; pair-bonds ended only as a result of the death of one pair member. However, molecular paternity analysis established that 35% of young were the result of extra-pair copulations (EPCs). This is the first study to provide strong evidence of long-term pair-bonds in a marsupial and raises questions about the relative benefits of pairing to males and females in this population.

White, David; Smith, V. Anne

doi: 10.1163/156853907782418259pmid: N/A

AbstractTechniques used to measure patterns of affiliation among social animals have rarely been tested for accuracy. One reason for this lack of validation is that it is often impossible to compare sample data to the true distribution of social assortment of a group of animals. Here we test some methods of assessing social assortment by using a computer simulation of organisms whose assortment patterns were under our control. We created male and female organisms that moved in a direction that was based on a social bias parameter. As the weight of this parameter increased, organisms were more likely to move in the direction of others of their sex. We then created virtual observers to sample assortment of the organisms under different social bias conditions. Observers used three different techniques of measuring assortment. These were (1) group membership: noting all organisms that were associated in the same 'group', (2) nearest neighbour: noting the nearest organism to a randomly selected individual and (3) neighbourhood: noting all organisms near a selected individual. Neighbourhood was taken either by all-occurrence sampling or by focal sampling the associations of randomly selected individuals. Some techniques emerged as more sensitive than others under different conditions and biases were revealed in some measures. For example, the group membership method was biased toward finding significant assortment differences between the sexes when no difference actually existed. Nearest neighbour was insensitive to finding a difference in assortment between sexes when one existed. Focal sampling was less sensitive to finding effects than all-occurrence sampling. The computer simulation revealed properties of each technique that would have been impossible to detect in the field.