Association patterns of spider monkeys: the influence of ecology and sex on social organization

Summary In this paper I consider how the costs and benefits of group living in spider monkeys (Ateles geoffroyi) vary between troop members. The results suggest that ecological factors set an upper limit to the number of spider monkeys that can associate and still efficiently exploit the available resources. In addition, the needs of the individual appears to influence the type and size of the subgroup it chooses. Adult males band together, travel over a large area, and are frequently sighted near the community's boundary. In contrast, adult females spend more time solitary than males and have association patterns that are strongly influenced by the presence of a dependent infant. Females with dependent infants tend to travel in small subgroups or alone, avoid the boundaries of the community's home range, and exhibit a restricted pattern of use of their range. The results suggest that males may be attempting to locate females with which they can breed, while mothers attempt to protect their infants by avoiding conspecifics and potentially dangerous situations near territorial boundaries.     

Comprehensive study of endocrine disrupting compounds using grab and passive sampling at selected wastewater treatment plants in South East Queensland, Australia

Chemical (gas chromatography-mass spectrometry, GC-MS) and biological (E-Screen assay) analyses were used to determine the concentrations of 15 endocrine disrupting compounds (EDCs) and estrogen equivalent (EEq) in grab and passive samples from five municipal wastewater treatment plants (WWTPs) in South East Queensland, Australia. EEq concentrations derived by E-Screen assays for the grab samples were between 108-356 ng/L for the influents and < 1-14.8 ng/L for the effluents with the exception of one effluent sample which was at 67.8 ng/L EEq. The EDC concentrations and EEq values for the passive samples were several times lower than those of the grab samples: a decrease probably caused by, but not limited to biofouling, low flow rate, biodegradation and temperature which can progressively reduce the uptake of compounds into the sampler. At this stage, grab sampling is the most reliable method for field monitoring; nevertheless, passive sampler is a useful sampling tool but the method requires more research to ensure that the information obtained can be interpreted appropriately. Although alkylphenols and phthalates were detected at higher concentrations in the wastewater samples as compared to natural hormones, the environmental risk may be negligible as their estrogenic potencies are several orders of magnitude lower than that of the natural estrogens. In most wastewater samples, the natural estrogens contributed to 60% or more of the EEq value. Removal efficacy of most estrogenic and xenoestrogenic compounds from the conventional activated sludge or biological nutrient removal (BNR) WWTPs monitored in this study was in the range of 80-> 99%. The efficiency of the WWTPs in removing estrogenic activity was > 95%. The EEqs of the E-Screen and those calculated from the results of extensive chemical analyses using the estradiol equivalency factors were comparable for most of the WWTPs samples.     

Intratree vertical variation of fruit density and the nature of contest competition in frugivores

Recently, we demonstrated that the highest densities of fruit pulp are located in the uppermost zones of tree crowns. Since heterogeneous distributions of depletable food is theorized to foster contest competition, we tested three hypotheses involving rank differences among species of arboreal frugivores: (1) In the absence of competitors, species tend to feed in higher strata of tree crowns; (2) interspecific contest competition occurs through monopolization and usurpation of feeding sites in these higher strata; and (3) subordinate species decrease their feeding height and ingestion rate when dominants enter the food patch. To test these hypotheses, we observed chimpanzees (Pan troglodytes), red-tailed monkeys (Cercopithecus ascanius), blue monkeys (Cercopithecus mitis), and gray-cheeked mangabeys (Lophocebus albigena) in Kibale National Park, Uganda. We found that: (1) all four primates fed preferentially in upper tree crowns when alone, (2) dominant species monopolized and aggressively usurped the upper crown when co-feeding with subordinates and the latter retreated below the middle of tree crowns, (3) in the presence of dominant species, subordinate species showed lower standardized feeding height and modified their food intake rates, while dominants were not affected by the subordinate species, (4) subordinates moved down at the arrival of and up at the departure of dominants, and (5) the presence of folivores in the tree did not affect the feeding height of a frugivore, even through folivores were socially dominant. Contrary to expectations, we found that red-tailed monkeys decreased their movements between successive fruits that they ate in the presence of blue monkeys compared to when they were feeding alone, perhaps to avoid disturbing dominants and attracting aggression or because they ingested more semi-ripe and green unripe fruits, i.e., more food of lower quality.     

Conspecific threat,predation avoidance,and resource defense: implications for grouping in langurs

Data on langur (Presbytis entellus) populations were gathered from the literature to test the importance of three selective pressures in determining group size and composition: predation pressure, intergroup resource defense, and conspecific threat. There were no detectable difference in the size of groups in populations facing nearly intact predator communities compared to those populations where predators were severely reduced in number or absent, although there was a trend for the number of adult males per group to increase in areas with nearly intact predator communities. Using population density as an indirect measure of the frequency of intrusions into a group’s home range and thereby as an index of the demographic pressure favoring resource defense, we predicted that higher densities would result in larger defensive coalitions and higher numbers of females per group. This prediction was not upheld. Our third selective pressure, conspecific threat, encompasses those selective forces resulting from physical attack on females, infants, and juveniles. Our index of conspecific threat uses the number of non-group males divided by the number of bisexual groups, because in langurs, the major source of conspecific threat derives from non-group males who, following group take-over, kill infants, wound females, and expel juveniles from groups. This index of conspecific threat was strongly related to the mean number of resident females, was weakly related to the mean group size, but was not related to the number of males in the group. In addition, as predicted, populations with a high index of conspecific threat had higher levels of juvenile expulsion. These analyses were corroborated by a simulation model which used a computer-generated series of null populations to calculate expected slopes of immatures regressed on adult females. These randomly generated populations, matched to means and ranges of real populations, allowed us to determine if deviations of the observed slopes from the expected null slopes could be explained by variation in predation pressure, population density, or conspecific threat. We found no evidence that predation pressure was associated with decreases in immature survival in smaller groups, as would be predicted by the predation-avoidance hypothesis. We found no evidence that immature survival was compromised by small group size in high-density populations, as would be predicted by the resource-defense hypothesis. However, as the index of conspecific threat increased, groups with larger numbers of females were more successful than groups with fewer females in reducing mortality or expulsion of immatures. Overall, conspecific threat received the strongest support as a selective pressure influencing langur group size and composition, suggesting that this selective pressure should be evaluated more widely as a factor influencing composition of animal groups. Received: 23 January 1995/Accepted after revision: 18 February 1996     

Seasonal growth in Laminaria longicuris: Relations with reserve carbohydrate storage and production

Growth rates of Laminaria longicruris increase during January and February, and the role of carbohydrate reserves as a carbon source for this growth was investigated. Seasonal variations in the levels of laminaran and mannitol showed maximum values for both in late summer. Minimum values occurred in February at the time when growth rates were increasing rapidly. Erosion of the blades in winter carried away much of the tissue containing carbohydrate reserves accumulated during the previous summer. Experimental reduction of carbohydrate reserves by fertilization with sodium nitrate during the summer did not affect subsequent winter growth rates. Truncation of the plants in November significantly reduced growth rates. The lower rate of growth is attributed to a reduction in photosynthetic area rather than a loss of storage products.NRCC No. 16478     

Testing sediment biological effects with the freshwater amphipod Hyalella azteca: the gap between laboratory and nature

The freshwater amphipod, Hyalella azteca, is widely used in laboratory sediment toxicity and bioaccumulation tests. However, its responses in the laboratory are probably very different from those in the field. A review of the literature indicates that in its natural habitat this species complex is primarily epibenthic, derives little nutrition from the sediments, and responds primarily to contaminants in the overlying water column (including water and food), not sediment or porewater. In laboratory sediment toxicity tests H. azteca is deprived of natural food sources such as algal communities on or above the sediments, and is subjected to constant light without any cover except that afforded by burial into the sediments. Under these constraining laboratory conditions, H. azteca has been reported to respond to sediment or porewater contamination. In nature, contamination of overlying water from sediment is less likely than in the laboratory because of the large, generally non-static sink of natural surface water. H. azteca does not appear to be the most appropriate test species for direct assessments of the bioavailability and toxicity of sediment contaminants, though it is probably appropriate for testing the toxicity of surface waters. Toxic and non-toxic responses will be highly conservative, though the latter are probably the most persuasive given the exposure constraints. Thus H. azteca is probably a suitable surrogate species for determining sediments that are likely not toxic to field populations; however, it is not suitable for determining sediments that are likely toxic to field populations.     

Nitrogen uptake characteristics of Chordaria flagelliformis (Phaeophyta) in batch mode and continuous mode experiments

The uptake of NH ₄ ⁺ and urea by Chordaria flagelliformis was measured in a perturbed system (batch mode) and in an apparent steady-state system (continuous mode). The maximum uptake rates (V_max) measured in short-term depletion experiments greatly exceeded those determined under a steady nutrient supply. C. flagelliformis briefly exposed to high nutrient concentrations has an impressive capacity for rapid uptake (high V_max)_which is uncoupled from growth. In contrast, under continous, homogenous low N concentrations the alga appears well equipped (low half-saturation constant, K_m) to take up the available N. The results show that previous work based on batch mode uptake experiments probably overestimated the N requirements for the growth of many seaweeds.     

Seasonal growth of Laminaria solidungula in the Canadian High Arctic in relation to irradiance and dissolved nutrient concentrations

Pontomyia is a genus of tiny flightless marine midges, with 4 described species, found on tropical or subtropical sea shores of the western Pacific Ocean. They are rarely noticed because of their small size (about 1.5 mm) and ephemeral adult life (1 to 3 h). They usually occur in association with seagrasses and seaweeds on which the larvae feed. The oar-like wings of adult males propel them over the water surface, but do not enable them to fly. Adult females are not only wingless but virtually legless. Emergence of the adults in the field may occur either during the day or at night. In a laboratory aquarium population of P. cottoni Womersley, maintained for about 18 months in a 12 h light-12 h dark cycle, males began to emerge at the end of the light period, whereas females emerged only after the onset of darkness. Field observations suggest that emergence times are probably influenced also by tides.     

How an introduced seaweed can affect epibiota diversity in different coastal systems

Invasions by non-indigenous species have the potential to alter the biodiversity of recipient systems. The magnitude of this effect often depends on the nature of the invaded communities and the ecology of the invader. We investigated the impacts of the Japanese seaweed Sargassum muticum (Phaeophyceae, Fucales) on biodiversity in a rocky and sedimentary environment on two islands in the North Sea. In each case, we compared the epibiota of non-indigenous S. muticum with epibiota communities on taxonomically related and structurally similar native seaweed hosts. Total and average species richness on S. muticum were similar on the rocky shore (60 species and 22±6 species, respectively) and the sandy shore (64 species and 20±3 species, respectively). However, community structure and species composition differed significantly between the environments. On the rocky shore, another native fucoid seaweed, Halidrys siliquosa, supported an epibiota community very similar to that of the invader. On the sandy shore, the only other abundant native habitat-providing algal species was Fucus vesiculosus. This species supported a different and less diverse assemblage of associated taxa. We conclude that S. muticum enhances epibiota diversity in the sedimentary environment, probably by increasing the substratum availability and habitat heterogeneity. In contrast, it has negligible impacts on epibiota diversity in the rocky shore environment, where it does not represent a fundamentally new habitat component. We conclude that even within the same region, the consequences of non-indigenous species on biodiversity cannot be generalised but depend on the composition and structural complexity of the species in the recipient community. This paper is dedicated to Udo Schilling, Chief Diving Officer, Alfred Wegener Institute who trained all of the authors in the waters off Helgoland to be scientific divers. The work reported here and in previous publications has been made possible through Udo’s training and support. We remain grateful for his enthusiasm, effort and patience.