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Alexander Skutch suggested that the threat of nest predation on tropical birds favors reduced activity near their nests. This hypothesis assumes that nest predation occurs during the day when adult birds are active, but few studies of tropical species have reported distributions of nest losses during the day-night cycle. We used thermistors placed in nests to record the time of nest predation events for species of understory rainforest birds during the incubation period. In our study, 14 of 21 nest-predation events (67%) occurred between 11:00 and 18:00 (EST), and none took place at night, between 19:00 and 06:00. Clearly, nest predation during incubation was primarily diurnal. Although a major premise of Skutch's hypothesis is supported, further research is needed to determine whether diurnal predators are attracted to nests by the movements of parent birds, begging of offspring, or other cues.

There is a growing interest in understanding the influence of plant traits on their ability to spread in non-native regions. Many studies addressing this issue have been based on relatively small areas or restricted taxonomic groups. Here, we analyse a large data base involving 1567 plant species introduced between Eastern Asia and North America or from elsewhere to both regions. We related the extent of species distributions in each region to growth form and the distinction between upland and wetland habitats. We identified significant relationships between geographical distribution and plant traits in both native and exotic ranges as well as regional differences in the relationships. Range size was larger for herbaceous graminoids and forbs, especially annuals compared to perennials, than for woody species, and range size also was larger for plants of wetland compared to upland habitats. Distributions were more extensive in North America than in Eastern Asia, although native plants from both regions had broader distributions than non-natives, with exotics from elsewhere intermediate. Growth form and environment explained more of the variance in distribution of plants in North America than in Eastern Asia. The influence of growth form and habitat on distribution suggests that these traits might be related to tolerance of ecological conditions. In addition, the smaller extents of species in non-native compared to native areas suggest roles for dispersal limitation and adaptation to region-specific ecological conditions in determining distribution.

Patterns of species richness reflect the balance between speciation and extinction over the evolutionary history of life. These processes are influenced by the size and geographical complexity of regions, conditions of the environment, and attributes of individuals and species. Diversity within clades also depends on age and thus the time available for accumulating species. Estimating rates of diversification is key to understanding how these factors have shaped patterns of species richness. Several approaches to calculating both relative and absolute rates of speciation and extinction within clades are based on phylogenetic reconstructions of evolutionary relationships. As the size and quality of phylogenies increases, these approaches will find broader application. However, phylogeny reconstruction fosters a perceptual bias of continual increase in species richness, and the analysis of primarily large clades produces a data selection bias. Recognizing these biases will encourage the development of more realistic models of diversification and the regulation of species richness.

The northern hemisphere tree genus Acer comprises 124 species, most of them monoecious, but 13 dioecious. The monoecious species flower dichogamously, duodichogamously (male, female, male), or in some species heterodichogamously (two morphs that each produce male and female flowers but at reciprocal times). Dioecious species cannot engage in these temporal strategies. Using a phylogeny for 66 species and subspecies obtained from 6600 nucleotides of chloroplast introns, spacers, and a protein-coding gene, we address the hypothesis (Pannell and Verdú, Evolution 60: 660-673. 2006) that dioecy evolved from heterodichogamy. This hypothesis was based on phylogenetic analyses (Gleiser and Verdú, New Phytol. 165: 633-640. 2005) that included 29-39 species of Acer coded for five sexual strategies (duodichogamous monoecy, heterodichogamous androdioecy, heterodichogamous trioecy, dichogamous subdioecy, and dioecy) treated as ordered states or as a single continuous variable. When reviewing the basis for these scorings, we found errors that together with the small taxon sample, cast doubt on the earlier inferences. Based on published studies, we coded 56 species of Acer for four sexual strategies, dioecy, monoecy with dichogamous or duodichogamous flowering, monoecy with heterodichogamous flowering, or labile sex expression, in which individuals reverse their sex allocation depending on environment-phenotype interactions. Using Bayesian character mapping, we infer an average of 15 transformations, a third of them involving changes from monoecy-cum-duodichogamy to dioecy; less frequent were changes from this strategy to heterodichogamy; dioecy rarely reverts to other sexual systems. Contra the earlier inferences, we found no switches between heterodichogamy and dioecy. Unexpectedly, most of the species with labile sex expression are grouped together, suggesting that phenotypic plasticity in Acer may be a heritable sexual strategy. Because of the complex flowering phenologies, however, a concern remains that monoecy in Acer might not always be distinguishable from labile sex expression, which needs to be addressed by long-term monitoring of monoecious trees. The 13 dioecious species occur in phylogenetically disparate clades that date back to the Late Eocene and Oligocene, judging from a fossil-calibrated relaxed molecular clock.

To evaluate the possibilities and limitations of using white-blood-cell (WBC) counts to characterize investment in immune-system function, we compared the prevalence and intensity of malaria infections and concentrations of WBCs in the American Robin (Turdus migratorius) in Michigan and Missouri and in the Clay- colored Robin (T. grayi) in central Panama. We ascertained infection by polymerase chain reaction (PCR) screening and quantified infection intensity and WBC concentrations by visual inspection of blood smears. Because few parasites were observed on smears, we assumed that most cases of malaria represented chronic, rather than acute, infections. Prevalence of haemosporidian infection (Panama 41%, Missouri 57%, Michigan 63%) did not differ significantly between locations. However, most infections in Panama were undetected on blood smears, whereas more than half were apparent on smears in Michigan and Missouri. Among WBCs, lymphocytes were the most abundant type, followed by heterophils; eosinophils and lymphocytes were more common in the North American sample than in Panama, and their numbers in Michigan were significantly higher in infected than in noninfected individuals. Tropical T. grayi apparently maintained infections at lower intensities but appeared to accomplish this in spite of lower abundances of immune-system cells. Furthermore, analyses of blood smears of Turdus spp. from elsewhere in the tropics revealed a wide range of prevalence, which suggests that either the regional presence of haemosporidians or the ability of hosts to control infections cannot be learned from limited samples. Additional species surveyed in Michigan and Panama revealed no consistent pattern in either infection intensity or WBC concentrations. Infection and response appear to be highly idiosyncratic. In agreement with other authors, we caution that blood parameters are difficult both to interpret and to sam- ple adequately in tests of regional or other effects.Prevalencia de Malaria y Respuesta de Glóbulos Blancos a la Infección en un Zorzal de la Zona Tropical y Uno de la Zona Templada

Phylogenetic analysis provides an important tool for assessing the influence of historical and evolutionary processes on the structure of contemporary ecological systems. Patterns of diversity, for example, represent the regional buildup of species through immigration and diversification, their loss through extinction, and the sorting of species ecologically within the region. Colonization-extinction dynamics on islands can be inferred from lineage accumulation through time. Lineage branching within clades can be used to estimate rates of speciation and extinction. However, simulations of these processes show potential ambiguities in the interpretation of data. Clade size is unrelated to age in many studies, suggesting that speciation and extinction might be in long-term equilibrium and raising questions about unobserved past diversity. Among passerine birds and other groups, the size of similar-aged clades is positively related to the size of the region within which they have diversified, and it is greater in tropical than in temperate regions. There is no consensus on the causes of these patterns. Finally, the ecological interactions between populations within regions brings the timescale of species sorting and species production close to each other and emphasizes the important interaction of ecological and evolutionary processes in shaping ecological systems.

For numerous taxa, species richness is much higher in tropical than in temperate zone habitats. A major challenge in community ecology and evolutionary biogeography is to reveal the mechanisms underlying these differences. For herbivorous insects, one such mechanism leading to an increased number of species in a given locale could be increased ecological specialization, resulting in a greater proportion of insect species occupying narrow niches within a community. We tested this hypothesis by comparing host specialization in larval Lepidoptera (moths and butterflies) at eight different New World forest sites ranging in latitude from 15 degrees S to 55 degrees N. Here we show that larval diets of tropical Lepidoptera are more specialized than those of their temperate forest counterparts: tropical species on average feed on fewer plant species, genera and families than do temperate caterpillars. This result holds true whether calculated per lepidopteran family or for a caterpillar assemblage as a whole. As a result, there is greater turnover in caterpillar species composition (greater beta diversity) between tree species in tropical faunas than in temperate faunas. We suggest that greater specialization in tropical faunas is the result of differences in trophic interactions; for example, there are more distinct plant secondary chemical profiles from one tree species to the next in tropical forests than in temperate forests as well as more diverse and chronic pressures from natural enemy communities.

Species turnover, or beta diversity, has been predicted to decrease with increasing latitude, but few studies have tested this relationship. Here, we examined the beta diversity-latitude relationship for vascular plants at a continental scale, based on complete species lists of native vascular plants for entire states or provinces in North America (north of Mexico). We calculated beta diversity as the slope of the relationship between the natural logarithm of the Jaccard index (lnJ ) for families, genera or species, and both geographic distance and climate difference within five latitude zones. We found that beta diversity decreased from south to north; within latitude zones, it decreased from species to genera and families. Geographic and climatic distance explained about the same proportion of the variance in lnJ in zones south of c. 50 degrees N. North of this latitude, nearly all the explained variance in lnJ was attributable to geographic distance. Therefore, decreasing beta diversity from south to north reflects decreasing climate differentiation within more northerly latitude zones, and primarily post-glacial dispersal limitation north of 50 degrees N.

We analysed the diversification of squamate reptiles (7488 species) based on a new molecular phylogeny, and compared the results to similar estimates for passerine birds (5712 species). The number of species in each of 36 squamate lineages showed no evidence of phylogenetic conservatism. Compared with a random speciation‐extinction process with parameters estimated from the size distribution of clades, the alethinophidian snakes (2600 species) were larger than expected and 13 clades, each having fewer than 20 species, were smaller than expected, indicating rate heterogeneity. From a lineage-through-time plot, we estimated that a provisional rate of lineage extinction (0.66 per Myr) was 94% of the rate of lineage splitting (0.70 per Myr). Diversification in squamate lineages was independent of their stem age, but strongly related to the area of the region within which they occur. Tropical vs. temperate latitude exerted a marginally significant influence on species richness. In comparison with passerine birds, squamates share several clade features, including: (1) independence of species richness and age; (2) lack of phylogenetic signal with respect to clade size; (3) general absence of exceptionally large clades; (4) over-representation of small clades; (5) influence of region size on clade size; and (6) similar rates of speciation and extinction. The evidence for both groups suggests that clade size has achieved long-term equilibrium, suggesting negative feedback of species richness on the rate of diversification.

Solitaires (Myadestes spp.) are montane-forest birds that are widely distributed throughout the New World, ranging from Alaska to northern Bolivia and including both Hawaii and the West Indies. To understand the origins of this impressive distribution, we used five mitochondrial gene sequences to reconstruct the historical biogeography of the genus. The resulting phylogeny indicates a rapid initial spread of the genus to occupy most of its contemporary continental range at least as far south as lower Mesoamerica, plus Hawaii and the Greater Antilles. The North American M. townsendi appears to be the sister taxon of the rest of Myadestes. Myadestes obscurus of Hawaii is more closely allied to Mesoamerican lineages than to M. townsendi. The strongly supported sister relationship of the two West Indian taxa, M. elisabeth and M. genibarbis, indicates a single colonization of the West Indies. A more recent node links the Andean M. ralloides to the Mesoamerican M. melanops and M. coloratus. A standard molecular clock calibration of 2% sequence divergence per million years for avian mitochondrial DNA suggests that the initial diversification of Myadestes occurred near the end of the Miocene (between 5 and 7.5 mya). Cooler temperatures and lower sea levels at that time would have increased the extent of montane forests and reduced overwater dispersal distances, possibly favoring range expansion and colonization of the West Indies. The split between South American and southern Mesoamerican lineages dates to ∼3 mya, which suggests that Myadestes expanded its range to South America soon after the Pliocene rise of the Isthmus of Panama. Despite the demonstrated capacity of Myadestes for long-distance dispersal, several species of Myadestes are highly differentiated geographically. Phylogeographic structure was greatest in the West Indian M. genibarbis, which occurs on several islands in the Greater Antilles and Lesser Antilles, and in the Andean M. ralloides. The phylogeographic differentiation within M. ralloides was not anticipated by previous taxonomic treatments and provides a further example of the importance of the Andes in the diversification of Neotropical birds. Overall, the historical biogeography of Myadestes suggests that range expansion and long-distance dispersal are transient population phases followed by persistent phases of population differentiation and limited dispersal. Biogeografía Histórica de los Zorzales del Género Myadestes

We measured the mass and several potential indices of functional capacity of the leg and pectoral muscles through 21 d of age in chicks of three species of galliform birds and the domesticated turkey. The study was conducted to test the hypothesis that the growth rate of a tissue is inversely related to its capacity for mature function across species. We measured the proportion of protein and the activities of the catabolic enzymes citrate synthase (CS), pyruvate kinase (PK), and beta -hydroxy-acyl-CoA-dehydrogenase (HOAD) and estimated exponential growth rate (EGR) from growth increments. EGR was negatively related to proportion of protein, PK, and HOAD and positively related to CS activity. In a multiple regression, EGR was uniquely related only to proportion of protein; it was higher in pectoral muscles and increased in this order: wild turkeypheasantdomestic turkeychukar. Thus, among wild species, the muscles of smaller species grew more rapidly for a given proportion of protein, but domestication and selection for rapid growth and large muscle size in turkeys resulted in substantially elevated growth rate. When the proportion of protein was normalized by its maximum value for each species and muscle type, the relationship between EGR and normalized protein did not differ significantly among species or muscle type. Thus, if we accept the proportion of protein relative to the mature level as an index of functional capacity--presumably representing the assembly of the contractile apparatus--then growth rate is consistently inversely related to a muscle's capacity for mature function, that is, force generation.

Islands have long provided material and inspiration for the study of evolution and ecology. The West Indies are complex historically and geographically, providing a rich backdrop for the analysis of colonization, diversification and extinction of species. They are sufficiently isolated to sustain endemic forms and close enough to sources of colonists to develop a dynamic interaction with surrounding continental regions. The Greater Antilles comprise old fragments of continental crust, some very large; the Lesser Antilles are a more recent volcanic island arc, and the low-lying Bahama Islands are scattered on a shallow oceanic platform. Dating of island lineages using molecular methods indicates over-water dispersal of most inhabitants of the West Indies, although direct connections with what is now southern Mexico in the Early Tertiary, and subsequent land bridges or stepping stone islands linking to Central and South America might also have facilitated colonization. Species–area relationships within the West Indies suggest a strong role for endemic radiations and extinction in shaping patterns of diversity. Diversification is promoted by opportunities for allopatric divergence between islands, or within the large islands of the Greater Antilles, with a classic example provided by theAnolislizards. The timing of colonization events using molecular clocks permits analysis of colonization–extinction dynamics by means of species accumulation curves. These indicate low rates of colonization and extinction for reptiles and amphibians in the Greater Antilles, with estimated average persistence times of lineages in the West Indies exceeding 30 Myr. Even though individual island populations of birds might persist an average of 2 Myr on larger islands in the Lesser Antilles, recolonization from within the archipelago appears to maintain avian lineages within the island chain indefinitely. Birds of the Lesser Antilles also provide evidence of a mass extinction event within the past million years, emphasizing the time-heterogeneity of historical processes. Geographical dynamics are matched by ecological changes in the distribution of species within islands over time resulting from adaptive radiation and shifts in habitat, often following repeatable patterns. Although extinction is relatively infrequent under natural conditions, changes in island environments as a result of human activities have exterminated many populations and others—especially old, endemic species—remain vulnerable. Conservation efforts are strengthened by recognition of aesthetic, cultural and scientific values of the unique flora and fauna of the West Indies.

We measured resting and peak metabolic rates (RMR and PMR, respectively) during development of chicks of seven species of shorebirds: least sandpiper (Calidris minutilla; adult mass 20 22 g), dunlin (Calidris alpina; 56-62 g), lesser yellowlegs (Tringa flavipes; 88-92 g), short-billed dowitcher (Limnodromus griseus; 85-112 g), lesser golden plover (Pluvialis dominicana; 150-156 g), Hudsonian godwit (Limosa haemastica; 205-274 g), and whimbrel (Numenius phaeopus; 380 g). We tested two opposing hypotheses: the growth rate-maturity hypothesis, which posits that growth rate in chicks is inversely related to functional maturity of tissues, and the fast growth rate-high metabolism hypothesis, which suggests that rapid growth is possible only with a concomitant increase in either RMR or PMR. We have found no evidence that chicks of shorebirds with fast growth rates have lower RMRs or lower PMRs, as would be predicted by the growth rate-maturity hypothesis, but our data suggested that faster-growing chest muscles resulted in increased thermogenic capacity, consistent with the fast growth-high metabolism hypothesis. The development of homeothermy in smaller species is a consequence primarily of greater metabolic intensities of heat-generating tissues. The maximum temperature gradient between a chick's body and environment that can be maintained in the absence of a net radiative load increased rapidly with body mass during development and was highest in least sandpipers and lowest among godwits. Chicks of smaller species could maintain a greater temperature gradient at a particular body mass because of their higher mass-specific maximum metabolic rates.

SUMMARYThe prevalence of vector-borne parasites varies greatly across host species, and this heterogeneity has been used to relate infectious disease susceptibility to host species traits. However, a few empirical studies have directly associated vector-borne parasite prevalence with exposure to vectors across hosts. Here, we use DNA sequencing of blood meals to estimate utilization of different avian host species by Culex mosquitoes, and relate utilization by these malaria vectors to avian Plasmodium prevalence. We found that avian host species that are highly utilized as hosts by avian malaria vectors are significantly more likely to have Plasmodium infections. However, the effect was not consistent among individual Plasmodium taxa. Exposure to vector bites may therefore influence the relative number of all avian Plasmodium infections among host species, while other processes, such as parasite competition and host-parasite coevolution, delimit the host distributions of individual Plasmodium species. We demonstrate that links between avian malaria susceptibility and host traits can be conditioned by patterns of exposure to vectors. Linking vector utilization rates to host traits may be a key area of future research to understand mechanisms that produce variation in the prevalence of vector-borne pathogens among host species.

Patterns of diversity within large regional biotas express the outcomes of processes, operating on both regional and local scales, that influence evolutionary diversification as well as the distribution and abundance of species. Regional analyses of species distributions suggest that neither ecological sorting of species based on their adaptations to the physical environment, nor interactions between competing species, adequately explain patterns of species richness. Potentially competing species appear to utilise broadly overlapping resources with similar proficiency. Phylogenetic and phylogeographic analyses reveal that species abundances and distributions within regions vary independently of evolutionary relationship. This implies the existence of dynamic, species-specific controls on population growth, as could be applied by specialised pathogens or other antagonists. Here, I argue that the changing balance of coevolved interactions between hosts and their antagonists shapes the distribution and abundance of individual host populations as well as patterns of local species richness. Geographical expansion creates allopatric populations and thereby could promote diversification; contraction ultimately leads to extinction. This taxon-cycle dynamic links regional diversity and distribution to intrinsic biological interactions independently of extrinsic ecological conditions. These hypotheses emphasise the central importance of investigating the impacts of pathogens on species abundance and distribution, and the potential consequences of coevolutionary changes in pathogen-host relationships for species formation and extinction.

Although some plant traits have been linked to invasion success, the possible effects of regional factors, such as diversity, habitat suitability, and human activity are not well understood. Each of these mechanisms predicts a different pattern of distribution at the regional scale. Thus, where climate and soils are similar, predictions based on regional hypotheses for invasion success can be tested by comparisons of distributions in the source and receiving regions. Here, we analyse the native and alien geographic ranges of all 1567 plant species that have been introduced between eastern Asia and North America or have been introduced to both regions from elsewhere. The results reveal correlations between the spread of exotics and both the native species richness and transportation networks of recipient regions. This suggests that both species interactions and human-aided dispersal influence exotic distributions, although further work on the relative importance of these processes is needed.

Understanding variation in resource specialization is important for progress on issues that include coevolution, community assembly, ecosystem processes, and the latitudinal gradient of species richness. Herbivorous insects are useful models for studying resource specialization, and the interaction between plants and herbivorous insects is one of the most common and consequential ecological associations on the planet. However, uncertainty persists regarding fundamental features of herbivore diet breadth, including its relationship to latitude and plant species richness. Here, we use a global dataset to investigate host range for over 7,500 insect herbivore species covering a wide taxonomic breadth and interacting with more than 2,000 species of plants in 165 families. We ask whether relatively specialized and generalized herbivores represent a dichotomy rather than a continuum from few to many host families and species attacked and whether diet breadth changes with increasing plant species richness toward the tropics. Across geographic regions and taxonomic subsets of the data, we find that the distribution of diet breadth is fit well by a discrete, truncated Pareto power law characterized by the predominance of specialized herbivores and a long, thin tail of more generalized species. Both the taxonomic and phylogenetic distributions of diet breadth shift globally with latitude, consistent with a higher frequency of specialized insects in tropical regions. We also find that more diverse lineages of plants support assemblages of relatively more specialized herbivores and that the global distribution of plant diversity contributes to but does not fully explain the latitudinal gradient in insect herbivore specialization.

Understanding the complexity of host immune responses to parasite infection requires controlled experiments that can inform observational field studies. Birds and their malaria parasites provide a useful model for understanding host-parasite relationships, but this model lacks a well-described experimental context for how hosts respond immunologically to infection. Here, ten canaries (Serinus canaria) were infected with the avian malaria parasite Plasmodium relictum (lineage SGS1) in a controlled laboratory setting with ten uninfected (control) birds. A suite of immunological blood parameters, including the concentration of four white blood cell types, the concentration of the acute phase protein haptoglobin, and the bacteria-killing ability of blood plasma, were repeatedly measured over a 25-day period covering the acute phase of a primary infection by P. relictum. Three infected and one control bird died during the course of the experiment. A multivariate statistical analysis of the immune indices revealed significant differences between infected and uninfected individuals between 5 and 14 days postinfection (dpi). Group differences corresponded to reduced concentrations of lymphocytes (5 dpi), heterophils (8 dpi), and monocytes (11 and 14 dpi), and an increase in haptoglobin (14 dpi), in infected birds relative to uninfected controls, and no change in bacteria-killing. Upon re-running the analysis with only the surviving birds, immunological differences between infected and control birds shifted to between 11 and 18 dpi. However, there were no clear correlates relating immune parameters to the likelihood of surviving the infection. The results presented here demonstrate the dynamic and complex nature of avian immune function during the acute phase of malaria infection and provide a context for studies investigating immune function in wild birds.

1 Using a simple technique for assessing constitutive innate immune function recently adapted for use in wild populations, we characterize changes in avian immune system development by repeated measurements of individuals over the period of nestling growth in a wild population of Leach's Storm-Petrels (Oceanodroma leucorhoa). 2 We measured levels of natural antibodies (NAb) during the early, middle and late phases of storm-petrel development and related these levels and NAb rate of change to mass and wing length growth. We used natural variation in nestling growth to assess the influence of nutritional status on the development of innate immunity. 3 NAb levels increased over the first 50 days of chick development; however, rate of increase was inversely proportional to wing growth. 4 Initial titre levels were inversely proportional to rate of change in NAb levels over the first 50 days of immune development. This suggests that individuals with low initial NAb levels accelerate immune development to reach adult levels, whereas individuals with high initial levels do not. 5 As in previous studies, our results demonstrate an inverse relationship between growth rate and development of components of the avian immune system. While such a relationship is consistent with the idea that immune function development involves trade-offs, the processes involved are more complex than simple energy allocation.

We studied the organization and temporal stability of an assemblage of ma- laria parasites (genera Plasmodium and Haemoproteus) and their passerine avian hosts in a forested study area in southern Missouri, USA, over four years. We detected parasite infections by polymerase chain reaction (PCR) of parasite DNA from host blood samples and identified parasite lineages by sequencing a part of the mitochondrial cytochrome b gene. We obtained 757 blood samples from 42 host species. Prevalence of malaria parasitism judged by PCR averaged 38.6% and varied in parallel in the three most abundant host species over the four years of the study. Parasite prevalence bore a U-shaped relationship to host sample size. Prevalence was weakly positively associated with host body mass, but not with foraging stratum, nest height, nest type, plumage brightness, or sexual dichro- matism. Over the sample as a whole, parasite prevalence did not vary between males and females or between hatch-year and older individuals. We differentiated 34 parasite lineages. The number of host species per lineage varied from one to eight and increased with sample size. We recovered up to 14 lineages of parasite from a single host. Three relatively common lineages in the Ozarks were found nowhere else; four others were recovered from other sites in eastern North America; and six additional well-sampled lineages were distributed in the Greater Antilles among resident island host species. Parasites that are endemic among native species of hosts on the tropical wintering grounds of Ozark birds were recovered from hatch-year birds in the Ozarks, indicating that transmission takes place on the summer breeding grounds, and consequently, that suitable vectors are present in both the temperate and tropical portions of the parasite lineage distributions. We estimate that the number of parasite lineages within a local area will approximate the number of host species and that our perception of host breadth and parasite diversity will increase for most lineages and hosts with increased sampling. Thus, host-parasite relationships in a local area, including the role of parasites in sexual selection and the evolutionary maintenance of sex, are likely to be complex, with population and evolutionary dynamics involving many actors.

We studied the relationship between one component of immune function and basal metabolic rate (BMR), an indicator of the ‘pace-of-life syndrome’, among 12 tropical bird species and among individuals of the tropical house wren (Troglodytes aedon), to gain insights into functional connections between life history and physiology. To assess constitutive innate immunity we introduced a new technique in the field of ecological and evolutionary immunology that quantifies the bactericidal activity of whole blood. Thisin vitroassay utilises a single blood sample to provide a functional, integrated measure of constitutive innate immunity. We found that the bactericidal activity of whole blood varied considerably among species and among individuals within a species. This variation was not correlated with body mass or whole-organism BMR. However, among species, bacteria killing activity was negatively correlated with mass-adjusted BMR, suggesting that species with a slower pace-of-life have evolved a more robust constitutive innate immune capability. Among individuals of a single species, the house wren, bacteria killing activity was positively correlated with mass-adjusted BMR, pointing to physiological differences in individual quality on which natural selection potentially could act.

Summary 1 Leach's Storm-Petrel (Oceanodroma leucorhoa) chicks accumulate fat through most of the nestling period, near the end of which they typically weigh 50–100% more than their parents. Much of this excess mass is lost abruptly prior to leaving the nest and fledging itself marks the termination of parental care. 2 In this study, we evaluated the hypothesis that the onset of the prefledging mass loss period coincides with the end of the development period and the completion of structural growth. 3 We characterized the pattern of prefledging mass loss and the timing of fledging with respect to a point (T), based on wing growth, at which structural development stops. Variation in T suggested that development rate is partially influenced by parental food provisioning, particularly early in the nestling period (age 16–20 days) just prior to the onset of rapid primary feather growth. 4 The timing of mass loss and fledging in relation to T suggested that prefledging mass loss begins upon completion of wing growth and that fledging occurs after chicks have reached a mass compatible with sustained flight. Thus, the time to fledging is positively correlated with nestling mass at the end of the development period. 5 The prefledging period of mass loss is a unique phase of anorexia placed between parental feeding and self-feeding in the life of the young petrel.

Methods to assess immunocompetence requiring only a single sample are useful in comparative studies where practical considerations prevent holding or recapturing individuals. The assay for natural antibody-mediated complement activation and red blood cell agglutination described here, requiring approximately 100 microl of blood, is highly repeatable. The effects of complement deactivation, 2-mercaptoethanol (2-ME), age, and lipopolysaccharide (LPS)-induced sickness response were examined to validate comparisons among diverse avian species. Complement deactivation by heating significantly reduces lysis and treatment with 2-ME reduces both lysis and agglutination. Lysis and agglutination both increase with age in chickens; LPS treatment does not influence these variables in 11-week-old chickens. In a comparison of 11 species, both lysis (0.0-5.3 titers) and agglutination (1.8-8.0 titers) vary significantly among species. Accordingly, this assay can be used to compare constitutive innate humoral immunity among species and with respect to age, sex, and experimental treatments within populations.

The diversity of a region reflects both local diversity and the turnover of species (beta diversity) between areas. The angiosperm flora of eastern Asia (EAS) is roughly twice as rich as that of eastern North America (ENA), in spite of similar area and climate. Using province/state-level angiosperm species floras, we calculated beta diversity as the slope of the relationship between the log of species similarity (S) and either geographic distance or difference in climate. Distance-based beta diversity was 2.6 times greater in the north‐south direction in EAS than in ENA and 3.3 times greater in the east‐west direction. When ln S was related to distance and climate difference in multiple regressions, both distance and climate PC1 were significant effects in the north‐south direction, but only geographic distance had a significant, unique influence in the east‐ west direction. The general predominance of distance over environment in beta diversity suggests that history and geography have had a strong influence on the regional diversity of these temperate floras.

Morphological diversity tends to increase within evolving lineages over time, but the relative roles of gradual evolutionary change (anagenesis) and abrupt shifts associated with speciation events (cladogenesis, or 'punctuated equilibrium') have not been resolved for most groups of organisms. However, these two modes of evolution can be distinguished by the fact that morphological variance increases in proportion to time under anagenesis, and in proportion to the logarithm of the number of species under cladogenesis. Although species and time are themselves correlated, multiple regression analysis provides a statistical framework for partitioning their relative contributions. In this study, I use multiple regressions to evaluate the effects of time and species number on morphological diversity within clades of passerine birds. The results show clearly that number of species exerts a strong influence on morphological variance independent of time, but that time has no unique effect. Thus, morphological evolution in birds seems to be associated with cladogenesis. How lineage splitting promotes morphological diversification poses an important challenge to ecologists and evolutionary biologists.

Cognition includes the acquisition, processing, retention of, and acting upon information from the environment. Avian cognition has been investigated by the approaches of experimental psychology and in the context of specific tasks, such as spatial memory. However, the costs and benefits of cognitive ability have not been considered in a life-history context. I explore possible relationships between behaviors that might indicate cognitive function and other attributes, particularly brain size, rate of development, age at maturity, and life span. Large brain size and prolonged development are seen as potential costs of intelligent behavior. Long life span may permit the extended learning periods that support experienced-based cognitive function. Play behavior, which plausibly supports the development of motor and social skills, and, to a lesser extent, foraging innovations, are related to brain size. The challenge of foraging in a spatially and temporally varying environment, experienced for example by pelagic seabirds, is associated with prolonged embryonic development. Although these connections lack mechanistic foundations, they suggest that cognition can be considered as a part of the life history of the individual and that potential costs of cognition might provide guidelines for directing the comparative study of intelligent behavior.

We comment on a recent paper by Francis and Currie that reports a globally consistent relationship between plant family diversity in large geographic grid cells and factors in the physical environment. This relationship was interpreted as demonstrating local ecological determination of diversity, leaving little room for regional and historical effects. We suggest that using family richness to describe patterns of diversity reduces regional effects owing to the lower endemism of plants at the family compared with the species level. Regardless of the taxonomic level of analysis, we further point out that unless regional effects are tested explicitly, statistically significant differences in diversity between regions can be overlooked. Finally, even correlations between diversity and physical conditions of the environment can have primarily historical and evolutionary origins when lineages diversify within ecological zones of origin and spread more slowly to diverse environments. Thus, local ecological determinism should not have primacy over evolutionary-historical explanations for patterns of diversity between or within regions. Ecologists must evaluate patterns in local diversity within historical and geographic, as well as ecological, contexts.

136.The greater number of plant species in temperate eastern Asia compared to easternNorth America has been ascribed to both local environment and regionalcharacteristics, but the relative contributions of each have not been resolved. In thisanalysis, we related species richness of flowering plants in mesoscale floras (B

Summary 1 We evaluated geographical and climate distributions of 57 vascular plant genera that have disjunct distributions primarily restricted to south-eastern Asia (EAS) and south-eastern North America (ENA). Because clades of each genus in the two regions are considered sister taxa, differences in ecological relationships between the regions reflect independent evolutionary responses to environmental factors and allow a test of ecological conservatism or parallelism. 2 The disjunct genera were found to be distributed in 270 grid cells, 163 in EAS and 107 in ENA, each with 3.75° extent in latitude and longitude. Individual disjunct genera occupied larger areas and latitudinal ranges in eastern Asia than in eastern North America, which parallels the larger area and latitudinal range of suitable climate in eastern Asia. 3 For all EAS-ENA disjunct genera taken together, the midpoint latitude, northernmost latitude, latitude range and area occupied were all significantly correlated between the two regions. For woody genera, only the correlation for midpoint latitude was significant, whereas for herbaceous genera, all except midpoint latitude were significant. 4 A twinspan analysis partitioned the grid cells into four distinctive groups based on presence or absence of the disjunct genera. Grid cells representing these groups in EAS and ENA remained clustered when plotted on axes defined by floristic ordination (non-metric multidimensional scaling) or climate variables (discriminant analysis), showing that the disjunct genera have similar floristic relationships to each other within regions and respond, to a large degree, in parallel to climate variables. 5 The lack of correlation in distribution variables among woody genera between the continents in part reflects the greater propensity of eastern Asian woody disjunct genera to extend southwards into subtropical and tropical latitudes. 6 Although the disjunct genera exhibit significant conservatism in geographical and climate distribution, reflecting their common evolutionary ancestry, differences between regions in geography, physiography and climate have also acted to diversify environmental relationships between continents.

Avian malaria is caused by a diverse community of genetically differentiated parasites of the genera Plasmodium and Haemoproteus. Rapid seasonal and annual antigenic allele turnover resulting from selection by host immune systems, as observed in some parasite populations infecting humans, may extend analogously to dynamic species compositions within communities of avian malarial parasites. To address this issue, we examined the stability of avian malarial parasite lineages across multiple time-scales within two insular host communities. Parasite communities in Puerto Rico and St Lucia included 20 and 14 genetically distinct parasite lineages, respectively. Lineage composition of the parasite community in Puerto Rico did not vary seasonally or over a 1 year interval. However, over intervals approaching a decade, the avian communities of both islands experienced an apparent loss or gain of one malarial parasite lineage, indicating the potential for relatively frequent lineage turnover. Patterns of temporal variation of parasite lineages in this study suggest periodic colonization and extinction events driven by a combination of host-specific immune responses, competition between lineages and drift. However, the occasional and ecologically dynamic lineage turnover exhibited by insular avian parasite communities is not as rapid as antigenic allele turnover within populations of human malaria.

The theoretical aerobic diving limit (tADL) specifies the duration of a dive after which oxygen reserves available for diving are depleted. The tADL has been calculated by dividing the available oxygen stores by the diving metabolic rate (DMR). Contrary to diving mammals, most diving birds examined to date exceed the tADL by a large margin. This discrepancy between observation and theory has engendered two alternative explanations suggesting that dive duration is extended either anaerobically or by depressing aerobic metabolism. Current formulations of tADL uncritically assume that DMR is independent of depth. However, diving birds differ from other vertebrate divers by having a larger respiratory system volume and by retaining air in their plumage while diving, thereby elevating buoyancy. Because air compresses with depth, diving power requirement decreases with depth. Following this principle, we modeled DMR to depth for Adelie and little penguins and reformulated the tADL accordingly. The model's results suggest thatapproximately 5% of natural dives by Adelie penguins exceed the reformulated tADL(d), or maximal aerobic depth, and none in the more buoyant little penguin. These data suggest that, for both small and large species, deep diving birds rarely if ever exceed tADL(d).

We examined the species-area relationship for three historically distinct subsets of Lesser Antillean birds identified by molecular phylogenetic analysis of island and continental populations. The groups comprised recent colonists from continental or Greater Antillean source populations, old taxa having recently expanded distributions within the Lesser Antilles, and old endemic taxa lacking evidence of recent dispersal between islands. The number of young taxa was primarily related to distance from the source of colonists in South America. In a multiple regression, the logarithmic slope of the species-area relationship for this group was shallow (0.066+/-0.016). Old endemic taxa were restricted to islands with high elevation, and within this subset, species richness was related primarily to island area, with a steep slope (0.719+/-0.110). The number of recently spread endemic taxa was related primarily to island elevation, apparently reflecting the persistence of such populations on islands with large areas of forested and montane habitats. Historical analysis of the Lesser Antillean avifauna supports the dynamic concept of island biogeography of MacArthur and Wilson, rather than the more static view of David Lack, in that colonists exhibit dispersal limitation and extinction plays a role in shaping patterns of diversity. However, the avifauna of the Lesser Antilles is probably not in equilibrium at present, and the overall species-area relationship might reflect changing proportions of historically distinguishable subsets of species.

We used phylogenetic analyses of cytochrome b sequences of malaria parasites and their avian hosts to assess the coevolutionary relationships between host and parasite lineages. Many lineages of avian malaria parasites have broad host distributions, which tend to obscure cospeciation events. The hosts of a single parasite or of closely related parasites were nonetheless most frequently recovered from members of the same host taxonomic family, more so than expected by chance. However, global assessments of the relationship between parasite and host phylogenetic trees, using Component and ParaFit, failed to detect significant cospeciation. The event-based approach employed by TreeFitter revealed significant cospeciation and duplication with certain cost assignments for these events, but host switching was consistently more prominent in matching the parasite tree to the host tree. The absence of a global cospeciation signal despite conservative host distribution most likely reflects relatively frequent acquisition of new hosts by individual parasite lineages. Understanding these processes will require a more refined species concept for malaria parasites and more extensive sampling of parasite distributions across hosts. If parasites can disperse between allopatric host populations through alternative hosts, cospeciation may not have a strong influence on the architecture of host-parasite relationships. Rather, parasite speciation may happen more often in conjunction with the acquisition of new hosts followed by divergent selection between host lineages in sympatry. Detailed studies of the phylogeographic distributions of hosts and parasites are needed to characterize these events.

The present study proposes to reconcile the different spatial and temporal scales of regional species production and local constraint on species richness. Although interactions between populations rapidly achieve equilibrium and limit membership in ecological communities locally, these interactions occur over heterogeneous environments within large regions, where the populations of species are stably regulated through competition and habitat selection. Consequently, exclusion of species from a region depends on long-term regional-scale environmental change or evolutionary change among interacting populations, bringing species production and extinction onto the same scale and establishing a link between local and regional processes.

The wide range in incubation periods among bird species has puzzled biologists for decades, because an extended egg-phase increases time-dependent mortality of the eggs.We investigated a recently proposed mechanistic explanation inspired by life-history theory, suggesting that adults may increase their own survival by reducing nest attentiveness, the percentage of daytime spent incubating eggs, in exchange for reduced offspring (egg) survival due to a longer incubation period. Incubation behaviour and egg temperatures (Tegg) of 14 bird species in the humid lowland tropics were studied to test the hypothesis that lower nest attentiveness and reduced Tegg cause longer incubation periods.Increased nest attentiveness correlated with higher average Tegg. However, neither nest attentiveness nor average Tegg was associated with the length of the incubation period. Longer off-bouts resulted in lower Tegg, but neither number of off-bouts nor off-bout length was associated with incubation period. In addition, we reanalysed a previously published negative association between Tegg and incubation period based on literature data from temperate passerine birds using a larger data set and found no significant correlation.In conclusion, our results do not support the hypothesis that longer incubation periods are caused by reduced nest attentiveness and corresponding lower Tegg.

During the past two decades, a critical need has developed to determine how exposure to contaminants in the environment affects individual and population processes. In this study, the immunocompetence of Western Bluebirds (Sialia mexicana) and Ash- throated Flycatchers (Myiarchus cinerascens) was studied on a landscape-soil contaminant gradient at Los Alamos National Laboratory (LANL) in New Mexico during 1997-1999. A variety of contaminants (heavy metals, chemicals, insecticides, polychlorinated biphenyls, and radioactive isotopes) range across different spatial scales and concentrations on LANL land. The two species have similar life-history traits, except that the Ash-throated Flycatcher has a faster rate of development and fledges 4-5 days earlier than the bluebird. The number of active nest boxes increased from 1997 to 1998 and 1999 for the Western Bluebird, but not for the Ash-throated Flycatcher. Survival of nestling flycatchers was lower in areas within 60 m of a potential contaminant release site, with a higher survivorship function associated with boxes farther away. The two species did not differ in their response to antigens, and there was no difference between locations for immunocompetence for either species. Flycatcher nestlings had a higher average cell-mediated response than bluebird nestlings, as predicted by the faster rate of development of the flycatchers. Phytohemag- glutinin response varied between locations for both species. The cell-mediated effects were dynamic in that, in general, the same locations showed similar patterns for each year. Hematocrits steadily increased with age for both species and varied between locations for the bluebird, but not the flycatcher.

We describe a polymerase chain reaction (PCR) assay that detects avian malarial infection across divergent host species and parasite lineages representing both Plasmodium spp. and Haemoproteus spp. The assay is based on nucleotide primers designed to amplify a 286-bp fragment of ribosomal RNA (rRNA) coding sequence within the 6-kb mitochondrial DNA malaria genome. The rRNA malarial assay outperformed other published PCR diagnostic methods for detecting avian infections. Our data demonstrate that the assay is sensitive to as few as 10(-5) infected erythrocytes in peripheral blood. Results of avian population surveys conducted with the rRNA assay suggest that prevalences of malarial infection are higher than previously documented, and that studies based on microscopic examination of blood smears may substantially underestimate the extent of parasitism by these apicomplexans. Nonetheless, because these and other published primers miss small numbers of infections detected by other methods, including inspection of smears, no assay now available for avian malaria is universally reliable.

We have analyzed birth records from the International Species Inventory System database of zoo animals to describe patterns of fertility as a function of age in birds and mammals. Unlike age at death, fertility in captive populations is partly controlled by animal keepers depending on availability of space and potential mates and on the aims of captive propagation programs. Thus, fertility records must be considered carefully to avoid potential age-specific biases. The zoo data suggest that fertility declines from a peak at young adult ages in most species. The rate of decline in reproductive function is correlated with the rate of somatic aging, indicated by the increase in mortality rate with age, and with the age at peak fertility. Over the sample as a whole, these patterns do not differ systematically between the sexes, nor do they differ between birds and mammals. While it is clear that the demographic consequences of aging of the reproductive system follow a different course than the aging of somatic tissue, the rates of each are correlated either through functional connections or through parallel evolutionary responses to common selective factors.

Summary 1West et al. (2001) describe a general model of ontogenetic growth in which growth represents the surplus of energy acquisition over maintenance energy requirement, which themselves are allometric (power) functions of body mass with exponents 3/4 and 1, respectively. Furthermore, the intercept of the maintenance requirement decreases with the –1/4 power of adult mass. 2These relationships determine the sigmoid shape of the postnatal growth curve and the 3/4 allometric slope of time to complete growth as a function of adult mass. 3West et al.'s growth function is a particular form of the generalized Putter growth model dm/dt = amy − bmz, which includes other familiar growth functions, such as the logistic and von Bertalanffy equations. 4Empirical estimates of the allometry of resting metabolism in growing birds are close to z = 1 in some precocial species, but are approximately 50% higher in altricial and semiprecocial birds, which challenges the generality of any single growth function for birds. 5Rather than growth rate being limited by the difference between energy acquisition and maintenance expenditure, it may also be determined by the growth potential of tissues, which is traded off against functional capacity. Predicted growth curves based on increasing tissue function with age are indistinguishable from the West et al. and related equations. 6Models based on growth rate–functional maturity trade-offs also can produce observed allometric relationships of growth rate to adult mass by incorporating the relative size of the chick at hatching. 7In contrast to West et al.'s model, declining variance in size among individuals as chicks approach adult size implies targeted growth and control of growth rate by feedbacks of body size itself on growth rate. 8The existence of plausible alternative hypotheses for the control of postnatal growth should stimulate additional experimental studies to elucidate mechanisms of growth rate regulation and to understand the evolutionary diversification of postnatal growth.

We studied time budgets of precocial chicks of American Golden-Plovers (Pluvialis dominica) on the tundra near Churchill, Manitoba, Canada, to assess how time budgets are influenced by environmental and body temperatures. Foraging time per day increased with increasing ambient temperatures and levels of solar radiation, as well as with age. This increase was due to an increase in the length of foraging bouts (i.e., the period of time in between two brooding bouts). The length of brooding bouts averaged 12 min, independent of ambient conditions or age. Body temperatures were lower under colder environmental conditions and increased as the chicks grew older. Based on measurements of cooling rates of penned chicks, we determined that at the end of a foraging bout, body temperature never fell below 35.5°C, which is high for a precocial chick. We suggest that in Churchill, American Golden-Plover chicks are not limited in their foraging time by ambient conditions, and they can collect sufficient food in the short periods of foraging that are available to them to sustain normal growth. By minimizing foraging bout length in favor of parental brooding, chicks may increase their digestive efficiency as well as save energy that would otherwise be expended on thermoregulation and locomotion. Presupuesto de Tiempo y Temperaturas Corporales de Polluelos de Pluvialis dominica y su Relación con la Temperatura Ambiental Resumen. Se estudió el presupuesto de tiempo de polluelos precociales de Pluvialis dominica en la tundra ubicada en las cercanías de Churchill, Manitoba, Canadá, para evaluar de qué manera el presupuesto de tiempo está influenciado por las temperaturas ambiental y corporal. El tiempo de forrajeo incrementó con el aumento de la temperatura ambiental, con los niveles de radiación solar y con la edad. Esto se debió a un incremento de la duración de las sesiones de forrajeo (es decir, el periodo de tiempo entre dos sesiones de empollamiento). La duración de las sesiones de empollamiento tuvo una media de 12 min, independientemente de las condiciones ambientales o de la edad. Las temperaturas corporales fueron inferiores bajo condiciones ambientales más frías, y aumentaron conforme a la edad de los polluelos. En base a medidas de la tasa de enfriamiento de pollos cautivos, es posible precisar que al final de una sesión de forrajeo, la temperatura corporal nunca es menor de 35.5°C, el cual es un valor elevado para un polluelo precocial. Sugerimos que en Churchill, el tiempo de forrajeo de los polluelos de P. dominica no está limitado por las condiciones ambientales y que los polluelos pueden acopiar suficiente alimento durante las cortas sesiones de forrajeo que disponen para mantener un crecimiento normal. La disminución de la duración de la sesión de forrajeo en favor de la incubación, les permite aumentar su eficacia digestiva y ahorrar energía, la que de otro modo podría emplearse en termorregulación o locomoción.

Many studies address the relationships between diversity or distribution and attributes of the physical environment. However, how these relationships are connected to variation in life history is poorly understood. This is particularly true in the case of pteridophytes. Japanese ferns and their allies comprise one of the best-known pteridophyte floras in the world. We analyzed ca 600 species of Japanese pteridophytes for which there is detailed information on distribution, reproduction, and chromosome number. Species richness was greatest in groups with a single reproductive mode (sexual, followed by apogamous), but distribution was greatest in species groups with multiple reproductive modes: sexual plus either sterile (irregular in meiosis) or apogamous. Geographical ranges varied greatly among species with small chromosome numbers but were uniformly small among species having high chromosome numbers. Seasonally green (mostly summer green) species had significantly larger distribution ranges than evergreen species. Endemic species had higher proportions of apogamy and sterility than non-endemic species. Seasonally green species had significantly larger distributional ranges, and a smaller proportion of species with apogamous reproduction, than evergreen species. There was no clear relationship between distribution and spore size, either among endemic species, non-endemic species, or all species combined. There was no relationship between spore size and chromosome number when all species were combined. However, positive relationships were detected within three of the nine largest genera, suggesting potential phylogenetic effects. We concluded that habitat availability, rather than dispersability, may be the limiting factor for the distribution of pteridophytes in Japan.

Wilson, D. S. 1992. The effect of complex interactions on variation between units of a metacommunity, with implications for biodiversity and higher levels of selection. Ecology 73:1984-2000. Wilson, D. S. 1997. Biological communities as functionally organized units. Ecology 78:2018-2024. Wilson, D. S., and W. G. Knollenberg. 1987. Adaptive indirect effects: the fitness of burying beetles with and without their phoretic mites. Evolutionary Ecology 1: 139-159. Wooton, J. T. 1994. The nature and consequences of indirect effects in ecological communities. Annual Review of Ecology and Systematics 25:443-466.

We identify and describe the distribution of 12 genetically distinct malaria parasite lineages over islands and hosts in four common passerine birds in the Lesser Antilles. Combined parasite prevalence demonstrates strong host effects, little or no island effect, and a significant host-times-island interaction, indicating independent outcomes of host-parasite infections among island populations of the same host species. Host- and/or island-specific parasite lineages do not explain these host-parasite associations; rather, individual lineages themselves demonstrate the same type of independent interactions. Unlike overall prevalence, individual parasite lineages show considerable geographic structure (i.e., island effects) as well as species effects indicating that parasite lineages are constrained in their ability to move between hosts and locations. Together, our results suggest an upper limit to the number of host individuals that malaria parasites, as a community, can infect. Within this limit, however, the relative frequency of the different lineages varies reflecting fine scale interactions between host and parasite populations. Patterns of host-parasite associations within this system suggest both historical co-evolution and ecologically dynamic and independent host-parasite interactions.

SUMMARYWind is a significant factor in the thermoregulation of chicks of shorebirds on the Arctic tundra. We investigated the effect of wind at speeds typical of near-surface conditions (0.1-3 ms-1) on metabolic heat production, evaporative cooling and thermal conductance of 1- to 3- week-old downy scolopacid chicks (least sandpiper Calidris minutilla;short-billed dowitcher Limnodromus griseus; whimbrel Numenius phaeopus). Body mass ranged from 9 to 109 g. To accurately measure the interacting effects of air temperature and wind speed, we used two or more air temperatures between 15° and 30°C that produced cold stress at all wind speeds, but allowed chicks to maintain normal body temperature(approximately 39°C). Thermal conductance increased by 30-50% as wind speed increased from 0.1 to 3 ms-1. Conductance in these chicks is somewhat lower than that of 1-day-old mallard ducklings of similar mass, but higher than values reported for downy capercaillie and Xantus' murrelet chicks, as well as for adult shorebirds. Evaporative water loss was substantial and increased with mass and air temperature. We developed a standard operative temperature scale for shorebird chicks. The ratio of evaporative cooling to heat production varied with wind speed and air temperature.

The rate of reproduction, age at maturity and longevity vary widely among species. Most of this life-history variation falls on a slow-fast continuum, with low reproductive rate, slow development and long life span at one end and the opposite traits at the other end. The absence of alternative combinations of these variables implies constraint on the diversification of life histories, but the nature of this constraint remains elusive. Here, we argue that individual and adaptive responses to different environments are limited by physiological mechanisms. Although energy and materials allocations are important results of physiological tradeoffs, endocrine control mechanisms can produce incompatible physiological states that restrict life histories to a single dominant axis of variation. To approach the problem of life-history variation properly, studies should integrate behavior and physiology within the environmental and demographic contexts of selection.

A few years ago, I had my first opportunity to visit the Amazonian Basin in eastern Ecuador. Several days of mist-netting and birding within an intact forest and in surrounding disturbed habitats turned out to be a pivotal experience, finally crystallizing in my mind a pattern that every Neotropical ornithologist knows but whose significance has largely escaped us. I am referring to the fact that most of the birds of the forest understory belong to the large South American endemic radiation of songbirds, the suboscines, called the infraorder Tyrannides (suborder Tyranni) by Sibley and Ahlquist (1990). This clade includes the ovenbirds, woodcreepers, antbirds, manakins, cotingas, and flycatchers, among others. Birds more familiar to North Americans, the oscine passerines (suborder Passeri), including the New World orioles, tanagers, and emberizine finches, dominate the forest canopy and habitats outside the forest, along with a few species-rich clades of tyrannine flycatchers (family Tyrannidae, subfamily Tyranninae). South America was an isolated island continent

Taxon cycles are sequential phases of expansion and contraction of the ranges of species, associated generally with shifts in ecological distribution. The important contribution of the taxon cycle to biogeographical analysis is its emphasis on evolutionary and ecological interactions among colonizing and resident species, which influence their extinction dynamics and establish patterns of geographical distribution. Taxon cycles were inferred originally from the distribution of species across island archipelagos, where a correlation was noted between gaps in island occupancy and the degree of phenotypic differentiation. This pattern implied that phases of colonization were followed by range contraction, while endemic Antillean species that were undifferentiated between islands suggested secondary expansion and the beginning of a new cycle. This interpretation was met with scepticism, but reconstruction of phylogenetic relationships from gene sequences has now permitted us to characterize taxon cycles in Lesser Antillean birds. The relative timing of phases of the cycle can be deduced from genetic divergence between island populations. We have found that taxon cycles have periods in the order of 10 6 years and that cycles in different lineages occur independently of each other and independently of Pleistocene climate cycles. Individual island populations may persist for several millions of years on the larger islands of the Lesser Antilles; occasional expansion phases lead to the replacement of island populations that have disappeared, thus reducing the archipelago-wide rate of extinction to nil. What drives taxon cycles is unknown, but we speculate that they may be caused by co-evolution with enemy populations, and a probable mechanism would involve infrequent mutations influencing parasite virulence and avian host disease resistance. Taxon cycles undoubtedly occur on continents, but the geographical configuration of island archipelagos reveals more clearly their presence and invites their study.

Historical biogeography is a study of taxa in time and space including their origin, migration and diversification. This kind of study requires fossil data and an understanding of phylogenetic relationships. These requirements make Acer a good model to study because Acer 1) has a relatively complete fossil record, 2) contains many species, 3) is a major northern temperate floristic element, and 4) is well known. Because fossils are only confidently assigned to section or species group, section as a unit is suitable for tracing evolutionary history of Acer. However, the circumscription of section of Acer is different to each classification through the long history of studies. This work reviews and summarizes the studying history of Acer. Delendick in 1981concluded that the system of Ogata in 1967 and that of Jong in 1976 were superior to others except that most Jong’s series should be raised to section. This work, therefore, follows Delendick’s delineation of section except Distyla and Parviflora, which are combined as Parviflora, to elucidate the development of the circumscription of section based on the system of Pax in 1885 and 1886, Pojarkova in 1933, Momotani in 1962, Fang in 1966, Ogata in 1967, Murray in 1970, Jong in 1976, Delendick in 1990 and Xu in 1996.

According to life-history theory, the development of immune function should be balanced through evolutionary optimization of the allocation of resources to reproduction and through mechanisms that promote survival. We investigated interspecific variability in cell-mediated immune response (CMI), as measured by the phytohaemagglutinin (PHA) assay, in relation to clutch size, longevity and other life-history traits in 50 species of birds. CMI exhibited significant repeatability within species, and PHA responses in chicks were consistently stronger than in adults. Univariate tests showed a variety of significant relationships between the CMI of both chicks and adults with respect to size, development period and lifespan, but not clutch size or prevalence of blood parasites in adults. Multivariate analyses confirmed these patterns but independent variables were too highly correlated to isolate unique influences on CMI. The positive relationship of chick CMI to nestling period is further complicated by a parallel relationship of chick CMI to the age at testing. However, multivariate analysis showed that chick CMI varies uniquely with length of the nestling period. Adult CMI was associated with a strong life-history axis of body size, development rate and longevity. Therefore, adult CMI may be associated with prevention and repair mechanisms related to long lifespan, but it also may be allometrically related to body size through other pathways. Neither chick CMI nor adult CMI was related to clutch size, contradicting previous results linking parasite-related mortality to CMI and the evolution of clutch size (reproductive investment) in birds.