The influence of food abundance,food dispersion and habitat structure on territory selection and size of an Afrotropical terrestrial insectivore

Most tropical insectivorous birds, unlike their temperate counterparts, hold and defend a feeding and breeding territory year-around. However, our understanding of ecological factors influencing territory selection and size in tropical insectivores is limited. Here we examine three prominent hypotheses relating food abundance, food dispersion (spatial arrangement of food items), and habitat structure to territoriality in the Usambara Thrush Turdus roehli. We first compared leaf-litter macro-invertebrate abundance and dispersion, and habitat structure between territories and random sites. We then examined the relation between these same ecological factors and territory size. Invertebrate abundance and dispersion were sparsely and evenly distributed across our study system and did not vary between territories and random sites. In contrast, habitat structure did vary between territories and random sites indicating the Usambara Thrush selects territories with open understorey and closed overstorey habitat. Invertebrate abundance and dispersion within territories of the Usambara Thrush were not associated with habitat structure. We believe the most likely explanation for the Usambara Thrush’s preference for open understorey and closed overstorey habitat relates to foraging behavior. Using information-theoretic model selection we found that invertebrate abundance was the highest-ranked predictor of territory size and was inversely related, consistent with food value theory of territoriality.     

Hominid paleoecology and competitive exclusion: Limits to similarity,niche differentiation,and the effects of cultural behavior

Fossil evidence from the Plio-Pleistocene of Africa apparently has confirmed a multi-lineage interpretation of early hominid evolution. Empirical refutation of the single species hypothesis must now be matched to the evolutionary ecology theory, which can underwrite taxonomic assessment and help to explain sympatric hominid coexistence. This paper contributes to that goal by reassessing the ecological rationale provided for the single-species hypothesis. Limiting similarity concepts indicate that the allowable ecological overlap between sympatric competitors is greater than the degrees of metric overlap often advanced as standards for identifying fossil species. Optimal foraging theory and the compression hypothesis show that the initial ecological reaction of a hominid to a sympatric competitor would likely be micro-habitat divergence and possibly also temporal differentiation of resource use. The long-term, evolutionary response is niche divergence, probably involving diet as well. General niche partitioning studies suggest that diet and habitat are the most common dimensions of niche separation, although temporal separation is unusually frequent in carnivores. The equation of niche with culture, basic to the single-species hypothesis, has no analytic meaning. Finally, four minor points are discussed, suggesting that (a) extinction is not unlikely, even for a long-lived and competitively competent hominid lineage, (b)parsimony is fickle, (c)interspecific mutualism may jeopardize survival, and (d)generalists are subordinate competitors, but for hominids, seemingly, successful ones. I argue that analog models of hominid paleoecology should be replaced by the use of zoological and anthropological observations to assess the generality and reliability of ecological theory and comcepts that may encompass early hominids.     

Habitat preference, escape behavior, and cues used by feather mites to avoid molting wing feathers

We analyzed the pattern of distribution and the effect of moltingon the escape behavior of feather mites on the wing feathersduring the nonmolting and molting season of the barn swallowHirundo rustica. Feather mites showed consistent preferencefor the second outermost primary, with a steady decrease inproximal distance and avoidance of the outermost primary. Severalexplanations are suggested to explain this unusual distribution.Further, analyzing the escape behavior of feather mites on moltingprimaries, we show that mites avoid the feathers destined tobe dropped next on molting barn swallows, and in the case ofthe outermost primary, mites use the "last moment" strategy,namely, leaving feathers shortly before it is dropped. Next,we performed an experiment in which we simulated shedding feathersor feathers about to be shed on nonmolting barn swallows, inorder to test cues used by feather mites in avoiding moltingprimaries. Both the vibration of the incised feather and thegap of the pulled feather induced mites to leave primaries situateddistally, at two-feathers distance from the manipulated primary,related to the control group. Our results show that feathermites have the ability to perceive the signal produced by thefeather that will drop next and by the gap of the missing feather.It remains to be demonstrated, whether feather mites have theability to perceive the vibration of the feather per se or theyperceive the altered airflow caused by the vibrating feathers.     

Threshold hypotheses,developmental age,and menstrual function

Hypotheses relating the onset and maintenance of menstrual function to threshold levels of various parameters have been subject to statistical critique. Analysis of trends in parameter variance, applied here to data from the Berkeley Guidance Study, discriminates between the predictions of such hypotheses and those of the more traditional concept of developmental age.     

How parasitoid females produce sexy sons: a causal link between oviposition preference, dietary lipids and mate choice in Nasonia

Sexual selection theory predicts that phenotypic traits used to choose a mate should reflect honestly the quality of the sender and thus, are often costly. Physiological costs arise if a signal depends on limited nutritional resources. Hence, the nutritional condition of an organism should determine both its quality as a potential mate and its ability to advertise this quality to the choosing sex. In insects, the quality of the offspring's nutrition is often determined by the ovipositing female. A causal connection, however, between the oviposition decisions of the mother and the mating chances of her offspring has never been shown. Here, we demonstrate that females of the parasitic wasp Nasonia vitripennis prefer those hosts for oviposition that have been experimentally enriched in linoleic acid (LA). We show by (13)C-labelling that LA from the host diet is a precursor of the male sex pheromone. Consequently, males from LA-rich hosts produce and release higher amounts of the pheromone and attract more virgin females than males from LA-poor hosts. Finally, males from LA-rich hosts possess three times as many spermatozoa as those from LA-poor hosts. Hence, females making the right oviposition decisions may increase both the fertility and the sexual attractiveness of their sons.     

Risk,mobility or population size? Drivers of technological richness among contact-period western North American hunter–gatherers

Identifying factors that influence technological evolution in small-scale societies is important for understanding human evolution. There have been a number of attempts to identify factors that influence the evolution of food-getting technology, but little work has examined the factors that affect the evolution of other technologies. Here, we focus on variation in technological richness (total number of material items and techniques) among recent hunter–gatherers from western North America and test three hypotheses: (i) technological richness is affected by environmental risk, (ii) population size is the primary determinant of technological richness, and (iii) technological richness is constrained by residential mobility. We found technological richness to be correlated with a proxy for environmental risk—mean rainfall for the driest month—in the manner predicted by the risk hypothesis. Support for the hypothesis persisted when we controlled for shared history and intergroup contact. We found no evidence that technological richness is affected by population size or residential mobility. These results have important implications for unravelling the complexities of technological evolution.     

Age-specific breeding success in a wild mammalian population: selection, constraint, restraint and senescence

The Selection, Constraint, Restraint and Senescence Hypotheses predict how breeding success should vary with age. The Selection Hypothesis predicts between-individual variation arising from quality differences; the other hypotheses predict within-individual variation due to differing skills or physiological condition (Constraint), residual reproductive lifespan (Restraint), or somatic and reproductive investment (Senescence). Studies tend to focus on either the initial increase in breeding success or later decrease; however, both require consideration when unravelling the underlying evolutionary processes. Additionally, few studies present genetic fitness measures and rarely for both sexes. We therefore test these four hypotheses, which are not mutually exclusive, in a high-density population of European badgers Meles meles. Using an 18-year data set (including 22 microsatellite loci), we show an initial improvement in breeding success with age, followed by a later and steeper rate of reproductive senescence in male than in female badgers. Breeding success was skewed within age-classes, indicating the influence of factors other than age-class. This was partly attributable to selective appearance and disappearance of badgers (Selection Hypothesis). Individuals with a late age of last breeding showed a concave-down relationship between breeding success and experience (Constraint Hypothesis). There was no evidence of abrupt terminal effects; rather, individuals showed a concave-down relationship between breeding success and residual reproductive lifespan (Restraint Hypothesis), with an interaction with age of first breeding only in female badgers. Our results demonstrate the importance of investigating a comprehensive suite of factors in age-specific breeding success analyses, in both sexes, to fully understand evolutionary and population dynamics.     

新疆开都河流域水生植物多样性及其影响因素

河流是一个连续的、流动的、独特而完整的系统,研究河流生态系统中水生植物的多样性分布格局及其影响因素对河流生态学研究具有重要意义。本文通过野外调查,研究了新疆开都河流域水生植物多样性、主要水生植物群落特征及与环境因子之间的关系,并利用水分-能量动态假说和栖息地异质性假说对该流域水生植物物种多样性的地理格局进行解释。结果表明: 开都河流域共有水生植物71种,隶属于24科39属;聚类分析可将开都河流域水生植物群落划分为10个主要群落类型,其中芦苇群落物种丰富度最高,狭叶香蒲群落和金鱼藻群落物种丰富度最低;流域水生植物群落Shannon指数与pH呈显著负相关,Simpson指数与pH、经度呈显著负相关,与海拔呈显著正相关;流域水生植物群落类型主要受海拔、水深及水温的影响;流域水生植物物种多样性随经纬度无明显变化规律。水分-能量动态假说和栖息地异质性假说共解释开都河流域水生植物多样性格局变量的31.4%,表明这两个假说对于该流域水生植物多样性格局的解释力并不高。     

Bird species richness patterns of northern Taiwan: primary productivity, human population density, and habitat heterogeneity

Energy, climate, habitat heterogeneity, and human activity are important correlates of spatial variation in species richness. We examined the correlation between species richness and these variables using the birds that breed in northern Taiwan. We conducted general linear models (GLMs) and spatial correlation models to examine the relationship between bird species richness (BSR) and environmental variables. We found that normalized difference vegetation index (NDVI) was the most important predictor of BSR. We suggest productivity is the primary process of BSR. Additionally, we hypothesized that scale dependency might exist in the relationship between BSR and NDVI in Taiwan. Human population density, the second most important factor, was inversely correlated with BSR. The factor and BSR did not have similar response to NDVI, which contradicted observations in most of the previous studies on human population vs. species richness. We proposed that the human population density had an effect on NDVI, which in turn had an effect on BSR. Moreover, we hypothesized that the contradiction between our study and the previous studies might arise from a higher level of human disturbance in Taiwan than in other areas. The necessity of conserving native species in intensively developed lowlands of Taiwan cannot be overemphasized. Number of land cover type was another significant predictor of BSR. Habitat heterogeneity may have an effect on BSR in Taiwan.     

Genetic sex determination,sex chromosome size and sex-specific lifespans across tetrapods

Sex differences in lifespan are ubiquitous across the tree of life and exhibit broad taxonomic patterns that remain a puzzle, such as males living longer than females in birds and vice versa in mammals. The prevailing unguarded X hypothesis explains sex differences in lifespan by differential expression of recessive mutations on the X or Z chromosome of the heterogametic sex, but has only received indirect support to date. An alternative hypothesis is that the accumulation of deleterious mutations and repetitive elements on the Y or W chromosome might lower the survival of the heterogametic sex (‘toxic Y’ hypothesis). Here, we use a new database to report lower survival of the heterogametic relative to the homogametic sex across 136 species of birds, mammals, reptiles and amphibians, as expected if sex chromosomes shape sex-specific lifespans, and consistent with previous findings. We also found that the relative sizes of both the X and the Y chromosomes in mammals (but not the Z or the W chromosomes in birds) are associated with sex differences in lifespan, as predicted by the unguarded X and the ‘toxic Y’. Furthermore, we report that the relative size of the Y is negatively associated with male lifespan in mammals, so that small Y size correlates with increased male lifespan. In theory, toxic Y effects are expected to be particularly strong in mammals, and we did not find similar effects in birds. Our results confirm the role of sex chromosomes in explaining sex differences in lifespan across tetrapods and further suggest that, at least in mammals, ‘toxic Y’ effects may play an important part in this role.     

The Evolution of Reversed Sexual Size Dimorphism in Hawks,Falcons and Owls: A Comparative Study

Many hypotheses have been proposed to account for the origin and maintenance of reversed size dimorphism (RSD, females being larger than males) in hawks, falcons and owls, but no consensus has been reached. I performed comparative analyses, using both cross-taxa data and phylogenetically independent contrasts, to investigate potential correlates of reversed size dimorphism. Using a similar set of explanatory variables, covering morphology, life history and ecology, I tested whether any trait coevolved with size dimorphism in all three groups and hence provided a general explanation for the evolution of RSD. For hawks, strong correlates were found in the foraging-variable complex, so RSD might have evolved in species hunting large and agile prey. This is consistent with the intersexual-competition hypothesis (sexes have evolved different sizes to lessen intersexual competition for food), but especially the small-male hypothesis (males have evolved to be smaller to be more efficient foragers). Evolutionary pathway analyses suggest that RSD evolved most likely as a precursor of changes in hunting strategy but as a consequence of high reproduction. The falcons showed a similar pattern: species with strong RSD hunted larger and more agile prey. The evolutionary pathway analysis supported the idea that RSD evolved before the specialisation on more agile and/or larger prey. Finally for owls, the results showed clear parallels. RSD increased with prey size, consistent with the small-male hypothesis. Evolutionary pathway analysis suggests that RSD in owls has most likely evolved before specialisation on large prey, so a small and more agile male might be advantageous even when hunting small prey. These results suggest that RSD in hawks, falcons and owls evolved due to natural-selection pressures rather than sexual-selection pressures. Co-ordinating editor: J. Tuomi     

The variations of human sex ratio at birth during and after wars, and their potential explanations

Data on wartime sex ratios (proportions male at birth) are reviewed. Two sorts of variation are empirically well supported viz. (a) rises during and just after both World Wars and (b) a fall in Iran during the Iran-Iraq War. Potential explanations are offered here for these rises and fall. The fall seems plausibly explained by psychological stress causing pregnant women disproportionately to abort male fetuses. The rises may be explained by either or both of two different forms of hypothesis viz. (i) Kanazawa's “returning soldier” hypothesis and (ii) variation in coital rates. The coital rate hypothesis potentially accounts, in slightly different ways, for the rises both during, and just after, some wars. The argument that coital rate affects sex ratio just after wars seems to be supported by evidence that in some combatant countries, dizygotic (DZ) twinning rates (which also reportedly vary with coital rate) peaked after the World Wars. The suggestion that war is associated with rises in sex ratio at birth was first made more than two centuries ago. However, I have been unable to locate direct supporting sex ratio data relating to any conflict before World War One. So it would be useful if historical demographers were to search for such data relating to these earlier wars.     

Long-term variability of meiobenthos: value,synopsis, hypothesis generation and predictive modelling

Few long-term data sets exist for meiofauna. Such data sets are expensive to collect, sort and identify; continuous meiofauna data for a period of greater than two years are limited to one site in Belgium (7 yrs) and two sites (one mud, one sand) in South Carolina, USA (11 yrs). The Belgian study concentrates on benthic copepod abundances whereas data from South Carolina includes major taxa and benthic copepods as well as 4 years of concurrent macrofauna abundance and 3 years of nematode species abundances. In South Carolina, the variance associated with meiofaunal abundance had 6 or 12 month recurrent cycles. Similar analyses on 4 years of macrofauna from the same 2 sites indicated the same cyclicity: one year. Seasonality of the South Carolina major taxa and the 6 most abundant mud copepod species was pronounced at the mud site, but absent or less pronounced at the sand site. Similar results were also found for the nematode species over three years. Variability in meiofaunal abundance was greater year-to-year than within a year. Many such long-term data sets are analysed and abandoned. Herewith, I use our long-term results to hypothesize the causes of the high temporal variance in mud and the lower temporal variance in sand. Is it because the mud fauna is controlled by seasonal inputs of natant predators while at the hydrodynamically active sand site temporal variability is homogenized by constant physical activity? By appropriate statistical modelling long-term data sets can also be used to assess the appropriateness of the sampling schedule (spatial and temporal) and as a predictor of future trends.     

Play behaviour in lowland gorillas: Age differences,sex differences,and possible functions

A study on lowland gorilla (Gorilla gorilla gorilla) play behaviour was conducted on four exhibits at three different zoological parks so that 19 gorillas were observed. Juvenile gorillas played the most, but play continued at fairly high frequencies through adolescence. Most social play occurred between dyads. Triadic groups usually chased each other. No sex differences in type of play were observed, but gender differences in partner preferences were observed. Males played with both other males and females, while females seldom played together. These data support the social skills hypothesis (Baldwin & Baldwin, 1974) of play. Data were gathered while the author was a graduate student at Tulane University and a visiting lecturer at the University of California, Riverside.     

Is there an influence of historical events on contemporary fish species richness in rivers? Comparisons between Western Europe and North America

Freshwater fish species richness on 132 West European and North American rivers is analysed using eleven variables related to contemporary ecology (nine) and history (two). This is done in order to examine the relative and joint effects of both historical and ongoing processes on the contemporary richness of these two regional fish faunas. Relationships are quantified by simple and stepwise multiple regression procedures. Species-area curves are presented for the fish faunas within both continents. We show that ecological factors statistically explain most of the variation in freshwater fish species richness for both continents. Effects of historical factors are shown to be statistically significant, but add only a little to the variance already explained by ecological factors. Our analyses further indicate that rivers (which flow directly into the ocean) support fewer species of fish than do similarly sized tributaries. The immigration-extinction hypothesis appears to provide a plausible explanation for this observed pattern. The fact that in our final model, a continental effect is still highly significant, leads us not to exclude the possibility of some other historical influences in generating different overall species richness levels on the two continents.     

Resource availability and growth responses to defoliation in seedlings of three early-successional,tropical, woody species

A growth experiment was conducted using seedlings of three early-successional, tropical, woody species:Dillenia suffruticosa (Dilleniaceae),Macaranga heynei (Euphorbiaceae) andTrema tomentosa (Ulmaceae). These species are characteristic of different positions along a soil fertility gradient in Singapore, withD. suffruticosa being the least andT. tomentosa the most demanding of high nutrient availability. The seedlings were grown in vermiculite at either low or high nutrient availabilities supplied by watering with different concentrations of a commercial plant food. Half the seedlings were subjected to a 50% defoliation at the start of the experiment by cutting off the distal half of each leaf. After 9 weeks the plants were harvested.Macaranga heynei andT. tomentosa seedlings showed no significant difference in parameters of growth such as total dry weight and total leaf area between the defoliated and control seedlings. The seedlings compensated completely for the loss of leaf area.Dillenia suffruticosa did show significant reductions in growth in some parameters due to defoliation, and these were more pronounced under the high nutrient treatment. These findings support the hypothesis that plants characteristic of resource-rich sites can readily recover from herbivory through fast growth, probably associated with a rapid turnover of leaves, whereas species of resource-poor habitats cannot easily replace losses due to herbivory and are adversely effected by defoliation.     

At the landscape level,birds respond strongly to habitat amount but weakly to fragmentation

Aim

It is usually thought that habitat fragmentation acts negatively on species survival, and consequently, on biodiversity. Recent literature challenges whether habitat fragmentation per se affects species richness, beyond the effect of habitat area. Theoretical studies have suggested that fragmentation may matter most when the amount of available habitat is small or at intermediate levels. However, a recent review suggests that the effect of fragmentation on species richness is usually positive. Here, we dissect the richness–fragmentation relationship. What is the effect size? Does it depend upon the amount of habitat cover? How do individual species respond to fragmentation?

Methods

Applying a macroecological approach, we empirically related avian richness and the probability of occurrence (p_occ) of individual species to fragmentation (number of patches), after controlling for habitat amount in 991 landscapes, each 100‐km², in southern Ontario, Canada.

Results

Species richness was strongly related to total habitat amount, but habitat fragmentation had no detectable additional effect. Individual species’ p_occ related strongly to habitat amount. For some species, p_occ also related secondarily to habitat fragmentation within landscapes. Logistic models revealed that p_occ related significantly negatively to fragmentation after controlling for habitat amount for only ~13% of forest‐ and 18% of open‐habitat species bird species. However, p_occ related significantly positively to fragmentation for even greater proportions of species, including some red‐listed species. Fragmentation effects were not stronger at low or intermediate levels of habitat amount within landscapes.

Conclusion

In earlier studies, negative effects of isolation were observed at the patch level in experimental manipulations. However, at the landscape level, avian species richness in southern Ontario apparently responds primarily to habitat amount and negligibly to fragmentation. We argue that the evidence is inconsistent with the hypothesis that reducing habitat fragmentation per se would be an effective conservation strategy for birds at the landscape level.