Intra- and interspecific morphological variation in the field mouse species Apodemus argenteus and A. speciosus in the Japanese archipelago: the role of insular isolation and biogeographic gradients

Two species of field mice, Apodemus argenteus and A. speciosus, occur in sympatry across the Japanese archipelago. The inter- and intraspecific patterns of morphological differentiation have been evaluated, using a Fourier analysis of the mandible outline. The relative importance of the effect of insular isolation and latitudinal climatic gradient on the size and shape of the two species was assessed by a comparison of the populations from the large island of Honshu and the surrounding small-island populations. The size variation in A. argenteus is correlated with the climatic gradient whilst the shape variation corresponds mainly to a random differentiation of the small-island populations from a Honshu-like basic morphological pattern. A. speciosus displays increased size on small islands, and its shape variation is related to both the climatic gradient and insularity. Finally, the two species are differentiated by both the size and shape of the mandible across the Japanese archipelago, suggesting that interspecific competition between both species is reduced via niche partitioning. Our results emphasize the importance of insular isolation on shape differentiation, but a part of the morphological differentiation is also related to the latitudinal climatic gradient. Isolation on small islands could have favoured such a response to environmental factors by lowering the gene flow that prevents almost any significant differentiation within Honshu populations.     

Ecotypic variation in the context of global climate change: revisiting the rules

Patterns of ecotypic variation constitute some of the few 'rules' known to modern biology. Here, we examine several well-known ecogeographical rules, especially those pertaining to body size in contemporary, historical and fossil taxa. We review the evidence showing that rules of geographical variation in response to variation in the local environment can also apply to morphological changes through time in response to climate change. These rules hold at various time scales, ranging from contemporary to geological time scales. Patterns of body size variation in response to climate change at the individual species level may also be detected at the community level. The patterns underlying ecotypic variation are complex and highly context-dependent, reducing the 'predictive-power' of ecogeographical rules. This is especially true when considering the increasing impact of human activities on the environment. Nonetheless, ecogeographical rules may help interpret the likely influences of anthropogenic climate change on ecosystems. Global climate change has already influenced the body size of several contemporary species, and will likely have an even greater impact on animal communities in the future. For this reason, we highlight and emphasise the importance of museum specimens and the continued need for documenting the earth's biological diversity.     

Evolution of restriction sites of ribosomal DNA in natural populations of the field mouse,Apodemus speciosus

An analysis by restriction endonuclease digestion of ribosomal DNA (rDNA) was carried out in natural populations of Apodemus speciosus, a field mouse that is endemic to Japan. Two restriction sites, the EcoRI (E3) and DraI (D4) sites, in the nontranscribed spacer region downstream from the gene for 28S RNA showed polymorphism within and between individuals in the populations from the Japanese main islands. By contrast, populations from the small adjoining islands which are thought to have separated from the main islands 1–2 × 10⁴ years ago showed relatively low levels of polymorphism within and between individuals, i.e., one of the polymorphic bands in the case of each enzyme was predominant in these populations, irrespective of the variants. These results indicate that the rate of fixation of site variations depends on population size and that the direction of fixation is random. Furthermore, each polymorphic restriction site seems to be fixed independently.Correspondence to: H. Suzuki     

Climate change and size evolution in an island rodent species: new perspectives on the island rule

As stated by the island rule, small mammals evolve toward gigantism on islands. In addition they are known to evolve faster than their mainland counterparts. Body size in island mammals may also be influenced by geographical climatic gradients or climatic change through time. We tested the relative effects of climate change and isolation on the size of the Japanese rodent Apodemus speciosus and calculated evolutionary rates of body size change since the last glacial maximum (LGM). Currently A. speciosus populations conform both to Bergmann's rule, with an increase in body size with latitude, and to the island rule, with larger body sizes on small islands. We also found that fossil representatives of A. speciosus are larger than their extant relatives. Our estimated evolutionary rates since the LGM show that body size evolution on the smaller islands has been less than half as rapid as on Honshu, the mainland-type large island of Japan. We conclude that island populations exhibit larger body sizes today not because they have evolved toward gigantism, but because their evolution toward a smaller size, due to climate warming since the LGM, has been decelerated by the island effect. These combined results suggest that evolution in Quaternary island small mammals may not have been as fast as expected by the island effect because of the counteracting effect of climate change during this period.     

Mandibles and molars of the wood mouse, Apodemus sylvaticus (L.): integrated latitudinal pattern and mosaic insular evolution

Aim The distinct nature of island populations has traditionally been attributed either to adaptation to particular insular conditions or to random genetic effects. In order to assess the relative importance of these two disparate processes, insular effects were addressed in the European wood mouse, Apodemus sylvaticus (Linnaeus, 1758). Location Wood mice from 33 localities on both mainland and various Atlantic and western Mediterranean islands were considered. This sampling covers only part of the latitudinal range of A. sylvaticus but included the two main genetic clades identified by previous studies. Islands encompass a range of geographical conditions (e.g. small islands fringing the continent through large and isolated ones). Methods The insular syndrome primarily invokes variations in body size, but ecological factors such as release from competition, niche widening and food availability should also influence other characters related to diet. In the present study, the morphology of the wood mice was quantified based on two characters involved in feeding: the size and shape of the mandibles and first upper molars. The size of the mandible is also a proxy for the body size of the animal. Patterns of morphological differentiation of both features were estimated using two‐dimensional outline analysis based on Fourier methods. Results Significant differences between mainland and island populations were observed in most cases for both the mandibles and molars. However, molars and mandibles displayed divergent patterns. Mandible shape diverged mostly on islands of intermediate remoteness and competition levels, whereas molars exhibited the greatest shape differentiation on small islands, such as Port‐Cros and Porquerolles. A mosaic pattern was also displayed for size. Body and mandible size increased on Ibiza, but molar size remained similar to mainland populations. Mosaic patterns were, however, not apparent in the mainland populations. Congruent latitudinal variations were evident for the size and shape of both mandibles and molars. Main conclusions Mosaic evolution appears to characterize insular divergence. The molar seems to be more prone to change with reduced population size on small islands, whereas the mandible could be more sensitive to peculiar environmental conditions on large and remote islands.     

A note on the presence of B chromosome in the small Japanese field mouse,Apodemus argenteus,in central Honshu,Japan

Previously, many studies have revealed the presence of B chromosomes in wild mouse taxa of the genus Apodemus (Rodentia, Muridae). In one of the Apodemus species, A. argenteus, which is endemic to Japan, it is known that B chromosomes were confirmed only in individuals (2n = 46 + B chromosome) from Hokkaido, Japan. There is no report of the presence of B chromosomes from other localities in the Japanese Islands. In this study, we analyzed the chromosomal constitutions of 43 individuals of A. argenteus from three localities in Honshu, Japan. A total of three individuals from central Honshu showed 2n = 47, and each individual carried a dot-like B chromosome. In addition, these B chromosome features were analyzed by differential staining methods, and the C- and QM-banding patterns of the B chromosomes were identical to those of the X chromosomal heterochromatic region showing the delayed-fluorescent response. Thus, it is considered that these B chromosomes would be derived from the heterochromatin of the X chromosomes, as reported in previously published papers.     

The tempo of genetic evolution in birds: body mass and climate effects

Aim Negative relationships between body mass and substitution rates have previously been reported. However, most of these studies have involved contrasted taxa that, due to their highly divergent phylogenetic histories, also differ in many additional characteristics other than mass. In particular, there has been little examination of the potentially confounding effects of climate or population size. Here we test for differences in rates of microevolution among bird species that, although differing in mass, are nonetheless very closely related phylogenetic pairs. We additionally tested for latitudinal/elevational and population size effects across these contrasts. Location Global. Methods The tempo of microevolution within the cytochrome b gene of mitochondrial DNA was compared between closely related bird species that differed in body mass, using 130 phylogenetically independent species pairs. In order to minimize climate effects, pairs not having overlapping latitudinal ranges were discarded. In addition, a subset of pairs was identified and analysed that involved comparisons between species that have different latitudinal or elevational midpoints. Results Species with smaller mass had substitution rates marginally faster than those with larger mass (small : large median ratio = 1.05). However, this result was only statistically significant when data were pruned to eliminate comparisons in which population or range size also varied substantially between contrasted species. Latitude and elevation had a much stronger association with substitution rates than body mass within the subset of pairs (n = 30) that also differed in their spatial distributions: lower elevation or latitude species had substantially more substitutions than those at higher latitudes or elevations (low : high ratio = 1.35). Furthermore, when the dataset was pruned of pairs in which body mass was confounded by latitude or elevation, the body mass effect was eliminated. Main conclusions Body mass is known to correlate with latitude, so that the latitudinal/elevational association with microevolution we found might either be additive to, or causal of, the body mass effect. These results are consistent with the evolutionary speed hypothesis, which suggests that latitudinal diversity gradients derive from variation in the rate of microevolution. Our findings also serve to raise concerns about biogeographical studies that use genetic distances between taxa to estimate time since divergence.     

Environmental influences on spatial and temporal patterns of body-size variation in California ground squirrels (Spermophilus beecheyi)

Aim  In order to understand how ground squirrels ( Spermophilus beecheyi ) may respond to future environmental change, we investigated five biotic and environmental factors potentially responsible for explaining body-size variation in this species across California. We examined the concordance of spatial patterns with temporal body-size change since the last glacial maximum (LGM).
Location  California, western North America.
Methods  We quantified body size of modern populations of ground squirrels ( n  = 81) and used a model-selection approach to determine the best variables (sex, vegetation, number of congeners, temperature and/or precipitation) explaining geographical variation in body size among modern populations. We also quantified body size of one fossil population in northern California ( n  = 39) and compared temporal body-size change in S. beecheyi at this location since the LGM with model predictions.
Results  Body size of modern populations conformed to Bergmann's rule, with larger individuals in northern (wetter and cooler) portions of California. However, the models suggest that precipitation, rather than temperature or other variables, may best explain variation in body size across modern spatial gradients. Our conclusion is supported by the temporal data, demonstrating that the body size of S. beecheyi has increased in northern California since the LGM, concordant with precipitation but not temperature change in the region.
Main conclusions  Precipitation, rather than temperature, vegetation or number of congeneric species, was the main factor explaining both spatial and temporal patterns of body-size variation in S. beecheyi . The integration of space and time provides a powerful mechanism for predicting how local populations may respond to current and future climatic changes.     

Population structure of the large Japanese field mouse, Apodemus speciosus (Rodentia: Muridae), in suburban landscape, based on mitochondrial D-loop sequences

Genetic structure of the large Japanese field mouse populations in suburban landscape of West Tokyo, Japan was determined using mitochondrial DNA control region sequence. Samples were collected from six habitats linked by forests and green tract along the Tama River, and from two forests segregated by urban areas from those continuous habitats. Thirty-five haplotypes were detected in 221 animals. Four to eight haplotypes were found within each local population belonging to the continuous landscape. Some haplotypes were shared by two or three adjacent local populations. On the other hand, two isolated habitats were occupied by one or two indigenous haplotypes. Significant genetic differentiation between all pairs of local populations, except for one pair in the continuous habitats, was found by analysis of molecular variance (amova). The geographical distance between habitats did not explain the large variance of pairwise F(ST)-values among local populations. F(ST)-values between local populations segregated by urban areas were higher than those between local populations in the continuous habitat, regardless of geographical distance. The results of this study demonstrated quantitatively that urban areas inhibit the migration of Apodemus speciosus, whereas a linear green tract along a river functions as a corridor. Moreover, it preserves the metapopulation structure of A. speciosus as well as the corridors in suburban landscape.     

Temperature effects on egg size and their fitness consequences in the yellow dung fly Scathophaga stercoraria

Organisms and parts of an organism like eggs or individual cells developing in colder environments tend to grow bigger. A unifying explanation for this Bergmann's rule extended to ectotherms has not been found, and whether this is an adaptive response or a physiological constraint is debated. The dependence of egg and clutch size on the mother's temperature environment were investigated in the yellow dung fly Scathophaga stercoraria. Smaller eggs were laid at warmer temperatures in the field and the laboratory, where possible confounding variables were controlled for. As clutch size at the same time was unaffected by temperature, this effect was not due to a trade-off between egg size and number. Temperature-dependent egg sizes even persisted within individuals: when females were transferred to a cooler (warmer) environment, they laid third-clutch eggs that were larger (smaller) than their first-clutch eggs. The fitness consequences of these temperature-mediated egg sizes were further investigated in two laboratory experiments. Neither egg and pre-adult survivorship nor larval growth rate were maximized, nor was development time minimized, at the ambient temperature corresponding to the mother's temperature environment. This does not support the beneficial acclimation hypothesis. Instead, this study yielded some, but by no means conclusive indications of best performance by offspring from eggs laid at intermediate temperatures, weakly supporting the optimal temperature hypothesis. In one experiment the smaller eggs laid at 24 °C had reduced survivorship at all ambient temperatures tested. Smaller eggs thus generally performed poorly. The most parsimonious interpretation of these results is that temperature-mediated variation in egg size is a maternal physiological response (perhaps even a constraint) of unclear adaptive value. This revised version was published online in November 2006 with corrections to the Cover Date.     

Variation at high latitudes: the geography of body size and cranial morphology of the muskox, Ovibos moschatus

Abstract Aim Bergmann's rule, one of the most studied and controversial ecogeographical generalizations, has rarely been tested with observations from high latitudes. We tested the rule using cranial measurements of the muskox [Ovibos moschatus (Zimmerman)], a homeotherm with an extremely northern distribution. We also used these data to describe geographical patterns in the species' dental architecture, an extension of the framework developed from interspecific comparisons. Location Specimens were compiled from arctic Canada, Alaska and Greenland, a latitudinal range of 60° N?83° N. Methods Body size was estimated from principal components analysis (PCA) of five cranial characters from 128 specimens. Mean scores on the first principal component from each locality were regressed against latitude and mean temperature to identify geographical variation in body size; scores on the second principal component were regressed against latitude to assess patterns in dental architecture. Regression analyses of the individual characters were performed as a complement to PCA. Results No latitudinal or climatic trend in body size was observed in either sex. On the other hand, for males, significant latitudinal variation was found for the second PCA axis (r = ?0.434), and the feature which loaded most heavily on it, maxillary tooth row length (r = 0.429). For females, this dental structure also tended to increase with latitude (r = 0.423), but the trend was only marginally significant (P=0.12), perhaps owing to a smaller sample size. Main conclusions The geographically invariant body size of muskoxen failed to support current hypotheses of size variation. Behavioural and physiological adaptations may exempt the muskox from selective pressures underlying these hypotheses. We interpret latitudinal variation in dental architecture as a reflection of a cline in diet, dominated by graminoids at the expense of willows at higher latitudes. This intraspecific geographical trend is a recapitulation of the interspecific framework for large mammalian herbivores.     

The acoustic ecology of an Amazonian bird assemblage: the role of allometry,competition and environmental filtering in the acoustic structure

Communication among birds constitutes the foundation of social interactions, and acoustic signals should evolve based on their efficiency to convey information. We examined the acoustic signals of an Amazonian bird assemblage by testing whether vocal allometry was the main driver in song evolution. We expected the acoustic parameters of the songs to follow general allometric rules, as the size of the vocal apparatus limits the vibration capacity of the syrinx. We tested whether smaller species use lower than expected frequencies due to environmental filtering by examining deviations from allometric relationships. Alternatively, small species could use higher than expected frequencies as a consequence of competitive processes that promote the use of vacant portions of the acoustic spectrum. We recorded birdsongs between 2013 and 2018 and measured three spectral parameters: the dominant frequency (FDOM), the minimum fundamental frequency (FFMIN) and the maximum fundamental frequency (FFMAX). We created an allometric model based on the acoustic pattern of the larger species and used it to predict the frequencies of the smaller species. We compared the frequency values expected by allometry with the observed parameters of the avian assemblage. We found that FDOM and FFMIN were higher than expected by allometry alone, supporting competition structuring in the acoustic ecology of the assemblage. The successful insertion of many species into the acoustic space is the result of long processes of natural selection, with our data highlighting the importance of competition in the vocal structuring of the community.     

蜂桶寨自然保护区中华姬鼠和社鼠肥满度的研究

我们于2008年4~11月对四川蜂桶寨自然保护区内中华姬鼠(Apodemus draco)和社鼠(Niviventer confucianus)肥满度在各年龄组及不同季节中的变化进行了研究,并初步分析了影响因素。结果显示：中华姬鼠肥满度在各年龄组中的性别差异不明显;在各年龄组间的差异显著,其变化趋势为老年组＞成年组＞亚成年组＞幼年组,亚成年组及老年组肥满度在各季节间无显著差异,而成年组则差异明显。社鼠肥满度在各年龄组间无显著性差异,亚成年组肥满度在各季节间差异显著,同时成年组及老年组肥满度在季节间无显著差异;二物种,亚成年组、成年组及老年组肥满度与海拔无明显的线性关系。分析认为,繁殖期能量的消耗的增加可能导致中华姬鼠肥满度在繁殖期下降,而社鼠成年及老年个体面对食物资源、能量需求等方面的季节变化,能够通过相应的调节,维持肥满度的稳定。     

Phenology, ontogeny and the effects of climate change on the timing of species interactions

Climate change is altering the phenology of many species and the timing of their interactions with other species, but the impacts of these phenological shifts on species interactions remain unclear. Classical approaches to the study of phenology have typically documented changes in the timing of single life-history events, while phenological shifts affect many interactions over entire life histories. In this study, we suggest an approach that integrates the phenology and ontogeny of species interactions with a fitness landscape to provide a common mechanistic framework for investigating phenological shifts. We suggest that this ontogeny–phenology landscape provides a flexible method to document changes in the relative phenologies of interacting species, examine the causes of these phenological shifts, and estimate their consequences for interacting species.
Ecology Letters (2010) 13: 1–10     

Testing Bergmann's rule in the presence of potentially confounding factors: a case study with three species of Galerida larks in Morocco

Aim  To test Bergmann's rule (which predicts a larger body size in colder areas within warm-blooded vertebrate species) in three partially sympatric species of larks ( Galerida theklae , Galerida cristata and Galerida randonii ) that occur in Morocco.
Location  Morocco.
Methods  Restriction fragment length polymorphism techniques applied on cytochrome b haplotypes were used to discriminate G. cristata and G. randonii , and to investigate the effects of interspecific hybridization in their contact zone. A comprehensive statistical framework was then designed to test Bergmann's rule in our three Galerida species (using altitude as a proxy for cold temperatures), while controlling for the possible influence of interspecific hybridization and competition and accounting for spatial autocorrelation. The method we propose is conservative in the sense that potentially confounding factors are adjusted so as to maximize their influence on the variable of interest.
Results  Bergmann's rule was strongly supported in G. theklae and G. randonii . However, body size did not respond to altitude in G. cristata , a result that was not simply explained by species-specific differences in geographical ranges and altitudinal span. In G. cristata , we detected a tendency for body size to increase with aridity, in agreement with an alternative definition of Bergmann's rule. However, since G. cristata also hybridizes with G. randonii in a contact zone located in the most arid part of the range of G. cristata , we could not tease apart the relative contribution of selection and hybridization in driving this pattern.
Main conclusions  This study highlights the need for careful statistical designs that allow meaningful variables to be picked out from large sets of potential factors. When taking these factors into account, we found that Bergmann's rule was still strongly supported in two out of the three species examined.     

Long‐distance call evolution in the Felidae: effects of body weight,habitat, and phylogeny

Long‐distance calls used for mate attraction and territorial spacing are distinctive signals in the felid vocal repertoire. Their evolution is subject to natural and sexual selection, as well as various constraints. Body size is an important morphological constraint, with the scaling of the spectral characteristics of a species' vocalizations with its body size being established for several vertebrate groups. Alternatively, the structure of long‐distance calls may have been optimized for transmission in species' habitats (acoustic adaptation hypothesis). The present study assessed whether the mean dominant frequency of long‐distance calls in the Felidae (approximately 70% of all species incorporated) is influenced by the species' body size and/or conforms to the acoustic adaptation hypothesis. After controlling for phylogenetic relationships, we found a significant correlation between mean dominant frequency of a taxon's long‐distance calls and conditions for sound transmission in its habitat type (‘open/heterogeneous’ versus ‘dense’), although no significant influence of body size. Taxa living in more open habitat types have long‐distance calls with significantly lower mean dominant frequencies than those living in dense habitats. The result obtained in the present analysis is fairly robust against random removal of single or few taxa from the data, and also against the use of different branch‐length transformation models in phylogenetic regression. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 487–500.     

Patterns of diversity, altitudinal range and body size among freshwater fishes in the Yangtze River basin, China

Aim To document patterns in diversity, altitudinal range and body size of freshwater fishes along an elevational gradient in the Yangtze River basin. Location The Yangtze River basin, China. Methods We used published data to compile the distribution, altitudinal range and body size of freshwater fishes. Correlation, regression, clustering and graphical analyses were used to explore patterns in diversity, altitudinal range and body size of freshwater fishes in 100‐m elevation zones from 0 to 5200 m. Results Species richness patterns across the elevational gradient for total, non‐endemic and endemic fishes were different. The ratio of endemics to total richness peaked at mid elevation. Land area on a 500‐m interval scale explained a significant amount of the variation in species richness. Species density displayed two peaks at mid‐elevation zones. The cluster analysis revealed five distinct assemblages across the elevation gradient. The relationship between elevational range size and the midpoint of the elevational range revealed a triangular distribution. The frequency distribution of log maximum standard length data displayed an atypical right‐skewed pattern. Intermediate body sizes occurred across the greatest range of elevation while small and large body sizes possessed only small elevational amplitudes. The size‐elevation relationship between the two major families revealed a very strong pattern of body size constraint among the Cobitidae with no corresponding elevational constraint and a lot of body size and elevational diversification among the Cyprinidae. Main conclusion The data failed to support either Rapoport's rule or Bergmann's rule.     

大林姬鼠两亚种线粒体DNA 细胞色素b 基因和控制区的序列多样性

为了研究大林姬鼠两亚种(韩国的指名亚种及中国东北和内蒙古地区的东北亚种)线粒体DNA 的变异程度并确定朝鲜亚种的分类地位,我们分别将来自韩国和中国东北长白山地区的两亚种的线粒体DNA 的细胞色素b 基因和控制区进行了测序分析。我们将测序所得到细胞色素b 基因序列与来自基因库的大林姬鼠5 个亚种的相应的单倍型进行了分析,结果显示大林姬鼠可分为4 个类群[类群1:韩国大林姬鼠指名亚种;类群2:中国长白山和内蒙古地区的东北亚种、俄罗斯外加贝尔的majuculus 亚种;类群3:中国长春的东北亚种、俄罗斯Primorye(俄罗斯远东地区) rufulus 亚种、俄罗斯库页岛(俄罗斯远东地区)和日本北海道地区的giliacus 亚种;类群4:中国黑龙江海林地区的东北亚种]。线粒体的控制区序列分析显示韩国指名亚种也不同于中国东北地区的东北亚种。本研究的类群1,2 和3 与Serizawa et al. (2002)的研究的K、S 和R 的分支相对应。这表明韩国指名亚种(类群1 和分支K)的线粒体DNA 与其他类群不同。另外,我们还发现在细胞色素b 基因构建的系统树中,东北亚种可以与类群2 (分支S)及类群3 (分支R 的不同亚种聚合在一起。我们认为线粒体DNA 的母性遗传与两个相邻亚种的个体之间的种内杂交造成了基于细胞色素b 序列对东北亚种的聚类分析结果与基于形态学特征的分类结果的不一致。因此,我们提出对这些显示出核苷酸序列多样性的东北亚种不能只用细胞色素b的数据进行亚种分类,还应该结合形态学和核DNA 特征进行进一步分析。最后,我们还发现韩国的指名亚种的细胞色素b 序列在平均距离16. 93% 的基础上不同于来自基因库的A. speciosus。Jones and Johnson (1965)指出了韩国的大林姬鼠在形态上的区别,所以我们认为韩国的大林姬鼠指名亚种A. p. peninsulae 是一种具有形态和遗传特异性的地方亚种。     

Macroecology and the hierarchical expansion of evolutionary theory

The constraint envelope describing the relationship between geographical range size and body size has usually been explained by a minimum viable population size model, furnishing a strong argument for species selection if geographical range size turns out to be ‘heritable’. Recent papers have questioned this assumption of nonzero geographical range heritability at a phylogenetic level, meaning that the logic that constraint envelopes provide support for higher‐level selection fails. However, I believe that analysis of constraint envelopes can still furnish insights for the hierarchical expansion of evolutionary theory because the fitness furnished by variation in body size, which is frequently measured as a highly ‘heritable’ trait at the species level, can be partitioned into anagenetic and cladogenetic components. The constraint envelope furnishes an explicit mechanism for large‐body biased extinction rates influencing the distribution of body size. More importantly, it is possible to envisage a scenario in which anagenetic trends driving an increase in body size in higher latitudes within species (Bergmann's rule) are counteracted by available habitat area or continental edges constraining overall species distribution in these higher latitudes, increasing the probability of extinction. Under this combined model, faunas at higher latitudes and under habitat constraints may reach equilibrium points between these opposing hierarchical adaptive forces at smaller body size than faunas with less intense higher‐level constraints and will tend to be more right‐skewed.