Geographic gradients in body size: a clarification of Bergmann's rule

1997 marked the sesquicentenary of the publication by Carl Bergmann of the observation that, in general, large-bodied animal species tend to live further north than their small-bodied relatives. This has been dubbed Bergmann's rule in his honour. However, more than 150 years on, we appear to be little closer to a general understanding of the rule, or even to any consensus as to whether it exists. This is due in large part to confusion about the taxonomic level at which the rule is considered to operate, and to the conflation of pattern and mechanism. In this paper, we attempt to resolve this confusion by highlighting its sources, and by providing a definition of Bergmann's rule that is practical and useful, yet that retains the essential features of its original formulation. We conclude by briefly reviewing the mechanisms proposed to explain Bergmann's rule as we define it.     

Known unknowns,Google Earth,plate tectonics and Mt?Bellenden Ker: some thoughts on locality data

Latitude/longitude data in locality records should be published with spatial uncertainties, datum(s) used and indications of how the data were obtained. Google Earth can be used to locate sampling sites, but the underlying georegistration of the satellite image should be checked. The little-known relabelling of a set of landmarks on Mt Bellenden Ker, a scientifically important collecting locality in tropical north Queensland, Australia, is documented as an example of the importance of checking records not accompanied by appropriately accurate latitude/longitude data.     

Testing for latitudinal and other body-size gradients

Testing for a relationship between the body size of animals and a gradient such as latitude is complicated by the fact that typically there is a single average size for each species, and each species occurs at several sample stations over the gradient. This results in standard tests for statistical significance being invalid. This problem can be overcome by using a randomization test. A more difficult problem, however, is determining whether the relationship between size and latitude is the same for two subfamilies of species. In this paper a general method for relating body size to latitude and subfamily differences is proposed, with the significance of effects determined by randomization. A simulation study suggests that this procedure has good properties. This approach to data analysis has promise both for the particular situation considered and for other related problems in biogeography.     

中国植物细根碳、氮、磷化学计量学的空间变化及其影响因子

为了研究中国陆地植物细根碳(C)、氮(N)、磷(P)的空间变化模式, 揭示细根在“温度-植物生理假说”及“生长速率假说”等方面的规律, 该文收集已发表的有关中国陆地植物细根研究的文献, 从中提取细根C、N、P元素含量及其相关数据, 分析了细根C、N、P含量及其比例与经纬度之间的关系。结果表明: 细根N、P元素含量均随纬度增加而增加, P含量随经度增加而降低, N:P随经度增加而增加。细根N、P含量与年平均气温、年降水量均呈负相关关系, 与土壤养分呈正相关关系。在土壤养分、温度、降水量3个非生物因素中, 土壤养分对细根N、P含量的影响最大。该文中细根和粗根的C:P、N:P差异变化不完全支持“生长速率假说”。根系和叶片一样, N、P含量与纬度呈正相关关系, 支持“温度-植物生理假说”, 反映了植物对自然环境的适应策略。     

Variable host quality, life-history invariants, and the reproductive strategy of a parasitoid wasp that produces single sex clutches

The parasitic wasp Achrysocharoides zwoelferi (Hymenoptera, Eulophidae) produces clutches consisting of only one sex. Moreover,male clutch size is invariably one while female clutches arein the range one to four. We designed field experiments todetermine the effect of host quality on clutch composition.We found that solitary male and solitary female clutches werereared from the same size mines, and that larger mines tendedto produce gregarious female clutches. A higher proportionof male clutches were placed in older hosts, despite theirlarge size. Variation in body size, both between and withinclutches, was measured in order to test the predictions of models that take into account the constraint that clutch size is aninteger trait, something of potential importance when absoluteclutch size is low. Our data supported several predictionsof these models, including the trade-off-invariant rule foroptimal offspring size developed by Charnov and Downhower.However, while most invertebrate clutch size models assume equal resource share among members of the same clutch, we found anincrease in inequality in larger clutches.     

Behavioral response of 12 ungulate species in captivity to the presence of humans

Twelve species of captive ungulates were studied to determine behavioral responses to the presence of a zookeeper within the exhibit and in front of the exhibit, with and without zoo visitors present. Significant differences in behavior occurred between species for nearly all behaviors observed. A significantly greater occurrence of vigilance and approach behavior was directed toward the zookeeper while within the exhibit relative to when the zookeeper stood in front of the exhibit. A significantly lower occurrence of eating or drinking occurred when the zookeeper was inside the exhibit. Significant differences occurred across size categories in the occurrence of approaching the zookeeper. The most frequently scored behavior was visual orientation. Statistically significant differences in the occurrence of visual orientation directed by females toward the zookeeper existed across size category, with more vigilance by species with larger body size. A statistically higher occurrence of vigilance toward the zookeeper was directed by female ungulates but not by males when the zoo was closed to the public. Although no statistical significance was found regarding the intraspecific vigilance of males, data on females revealed significant differences across species and across size categories. When data regarding vigilance toward the public were analyzed, statistically significant differences existed between species for females only. Likewise, when data regarding interspecific vigilance were examined, statistically significant differences were found across size categories for females, but not for males. The potential roles of vigilance in the wild are discussed in reference to its role in captivity.     

Ecological correlates of body size and egg size in parasitic Ascothoracida and Rhizocephala (Crustacea)

In order to identify key factors in the evolution of life history traits in Ascothoracida and Rhizocephala (two groups of crustacean parastes of invertebrates), comparative analyses were performed using phylogenetically independent contrasts. Among 59 ascothoracidan species, latitude correlated positively with body size, whereas there was no relationship between water depth and body size. Body size also correlated strongly with egg size; however, once corrected for body size, egg size was not related to either latitude or water depth. Among 91 rhizocephalan species, neither latitude nor water depth correlated with body size. However, host species of larger sizes harboured larger species of rhizocephalan parasites. Egg size of rhizocephalans did not correlate with body size, and was not influenced by either latitude or water depth. The patterns observed in this study show both differences from an similarities to those reported for other groups of crustacean parasites, and suggest that adaptations to similar selective pressures are not always identical among distantly-related taxa.     

性别、季节和体型大小对吐鲁番沙虎巢域的影响

2008年6月份至2009年5月份对吐鲁番沙虎的巢域进行调查:2008年6月份至2008年8月份为繁殖季节(RS),2008年9月份至2009年5月份(冬眠期除外)为非繁殖季节(NRS)。利用截趾标志重捕法研究吐鲁番沙虎的巢域,共标记283只吐鲁番沙虎,累计繁殖季节24只,非繁殖季节43只重捕超过3次(其中13只个体在繁殖季节和非繁殖季节均够3次以上捕捉次数,为重复个体),可以用于计算个体巢域面积数据。利用软件MapGis计算最小凸多边形法(MCP)巢域面积,并分析性别、体型大小、季节等因素对巢域的影响。结果表明:吐鲁番沙虎非繁殖季节雄性、雌性与幼体各组间的巢域面积差异均显著,繁殖季节巢域面积差异不显著;雌雄个体不同季节或全年合并比较巢域面积差异性均不显著;非繁殖季节面积与吻肛长(SVL)显著相关、全年成体组的巢域面积与吻肛长显著相关;成体巢域面积季节差异显著(U=41,P=0.046),幼体则没有季节差异(U=159,P=0.537)。因而,吐鲁番沙虎的巢域大小受性别因素影响不大,体型大小对巢域面积有显著影响,由于繁殖、食物资源等的季节变化是影响吐鲁番沙虎巢域最重要的因素。     

Limited gene flow may enhance adaptation to local optima in isolated populations of the Roesel's bush cricket (Metrioptera roeselii)

Variation in morphological traits along latitudinal gradients often manifests as size clines. In insects, both positive and negative correlations are seen, and the mechanism behind the response is unclear. We studied variation in seven morphological traits of Roesel's bush cricket, Metrioptera roeselii, sampled from seven latitude-matched-pair populations that were either geographically isolated from or connected to the species continuous distribution range. The aim was to examine whether morphological traits differed between isolated and continuous populations, and whether latitudinal variation was apparent. The data were used to indicate whether variation in trait means originates from plastic responses to the environment or genetic adaptation to local conditions. To evaluate the influence of gene flow on trait means, we analysed the genetic variation in seven microsatellites. Data showed that individuals from isolated populations display a positive relationship between latitude and body size, whereas individuals from continuous populations show little or no such relationship. The combined morphological and genetic data suggest that the isolated populations have adapted to local optima, while gene flow between continuous populations appears to counteract this process.     

Variation in life-history characteristics among populations of North American wood turtles: a view from the north

Life-history traits such as age at maturity, body size and clutch size tend to vary across a species' distribution. The purpose of our study was to describe the demography of a newly discovered population of North American wood turtles Glyptemys insculpta at the species' northern range limit, and to compare our findings to those of other studies to test hypotheses about adaptive life-history variation. Turtles were hand-captured from May to October 2005 and 2006 along a 4.5 km stretch of river located in the Sudbury District, ON, Canada (46°N). Fifty-five captured individuals provided a population density estimate of 1.3 turtles/100 m of river. Juveniles comprised 35% of wood turtles captured, and growth ring counts (i.e. age estimates) indicated recruitment in each of the past 11 years. Among populations, we found a nonlinear pattern in body size variation with the largest turtles in the north, smallest turtles in the centre of the range, and intermediate-sized turtles in the south. This nonlinear pattern in body size was reflected in clutch size variation. Selective pressures to overcome years of low recruitment may have resulted in larger body sizes and hence large clutch sizes at northern latitudes while conspecifics at southern latitudes can achieve larger body sizes because they live in a more productive environment. Population density decreased with latitude, likely as a result of a gradient in habitat productivity.