Biology subjects

Sheard, C.

Publications and source records attributed to Sheard, C..

9 recordsLinked to original sources

bioRxiv2026

Evolutionary dynamics of temporal niche among tetrapods

The diversification of biodiversity progresses as newly evolving species adapt to occupy available niche space - including the temporal dimension. Throughout the history of life, animal species adapted to occupy specific regions, or all regions (cathemerality), of the day-night temporal spectrum. While adaptive radiation theory is predicted to drive much of the global proliferation of biodiversity, the role that the day-night temporal dimension plays in offering ecological opportunity for lineages to diversify remains fundamentally neglected. Using a dataset spanning 19,940 species from across all four main tetrapod lineages (amphibians, squamates (restricted to lizards), mammals and archosaurs), we perform the very first evolutionarily standardised temporal niche diversification analysis and the first to include substantial number of ectotherms. We examine temporal niche as a source of ecological opportunity for adaptive radiation and contrast how lineages have leveraged ecological opportunity spread across 24h time. Findings revealed that tetrapods most frequently transitioned towards diurnality, suggesting a general opening of ecological opportunity in diurnal niche space since the K-Pg mass extinction. Moreover, amphibians are faster and more flexible than amniotes in temporal niche evolution, supported by a relatively higher speed of temporal niche transition and by spending relatively more in time cathemerality, potentially compensating for limitations in geographic dispersal. This interpretation suggests the day-night temporal niche dimension interacts with the geographic dimension, as it exhibits processes which unfold in parallel to (independent of) the geographic dimension as well as processes which unfold in response to what occurs in the geographic dimension.

evolutionary biology↗

bioRxiv2025

Temporal niche influences higher extinction risk among diurnal tetrapods from tropical regions

Anthropocene extinctions of biodiversity vary dramatically through geographic and phylogenetic space, with certain regions and lineages concentrating high defaunation rates, while others remain nearly unchanged.This heterogeneity in biodiversity erosion results from (spatial and phylogenetic) variation in the interactions between species fitness-relevant traits and environmental threats that trigger extinctions. Evidence reveals that factors including life histories, ecophysiology, and resource-use generalism influence variation in species declines under rapidly changing environments. An emerging hypothesis predicts that species spread across different locations of the 24h diel spectrum are exposed to different anthropogenic pressures on demographic stability (e.g. daytime contact with humans), which can trigger differential extinction risk among diurnal, nocturnal and cathemeral (day-night active) species. However, this hypothesis remains largely neglected. Only a single large-scale test exists, which documented higher declines among diurnal mammals. Here, we address this hypothesis across tetrapods globally, spanning >23,000 species across both endotherms and ectotherms for the first time. Our results reveal that cathemerality is significantly associated with a lower probability of undergoing population declines across tetrapods (except birds), while diurnality is associated with higher extinction risk category in amphibians. Collectively, our results suggest that the role of temporal niche in extinction is significant but variable across tetrapods.

evolutionary biology↗

bioRxiv2023

Anthropogenic nest material use correlates with human landscape modifications in a global sample of birds

As humans increasingly modify the natural world, many animals have responded by changing their behaviour. Predicting the extent of these responses is a key step in conserving these species. For example, the tendency for some species of birds to incorporate anthropogenic items - particularly plastic material - into their nests is of increasing concern, as in some cases this behaviour has harmful effects on both adults and young. Studies of this phenomenon, however, have to date been limited in geographic and taxonomic scope. To investigate the global correlates of anthropogenic (including plastic) nest material use, we used Bayesian phylogenetic mixed models and a dataset of recorded nest materials in 6,147 species of birds. We find that after controlling for research effort, anthropogenic nest material use is correlated with proximity to human landscape modification, synanthropic (artificial) nesting locations, breeding environment, and the number of materials that has been recorded within the species nest. We also demonstrate that anthropogenic nest material use is unrelated to body mass, range size, or conservation status. These results indicate that anthropogenic materials are more likely to be included in nests when they are more readily available, as well as potentially by species who have more flexibility in nest material choice.

evolutionary biology↗

bioRxiv2023

Nest traits for the world's birds

MotivationA well-constructed nest is a key element of successful reproduction in most species of birds, and nest-building strategies vary widely across the class. Macroecological and macroevolutionary studies tend to group nest design into a small number of discrete categories, often based on taxonomic inference. In reality, however, many species display considerable intraspecific variation in their nest-building behaviour, and broad-level categories may include many functionally distinct nest types. To address this confusion in the literature and facilitate future studies of broad-scale variation in avian parental care, we here introduce a detailed, global comparative database of nest building in birds, together with preliminary correlations between these traits and species-level environmental variables. Main types of variable containedWe present species-level data for nest structure, location, height, material composition, sex of builder, building time, and nest dimensions. Spatial location and grainGlobal. Maps are presented at the 1{degrees}x1{degrees} level. Time period and grainIncluded species are generally extant, although we present some data for recently extinct taxa. The data was collected 2017-2021 and was drawn from secondary sources published 1992-2021. Major taxa and level of measurementPartial or complete trait data is presented for 8,601 species of birds, representing 36 of 36 orders and 239 of 243 families. Software formatData have been uploaded as Supplementary Material in .xlsx format and are separated by species and source for all traits (S1) as well as summarised at the species level for structure and location variables (S2).

evolutionary biology↗

bioRxiv2023

The macroevolutionary dynamics of mammalian sexual size dimorphism

Sexual size dimorphism (SSD) is a common phenomenon across the animal kingdom. Mammals are unusual in primarily displaying male-biased SSD, where males of a species are typically larger than females. The driving factors behind the evolution of this SSD have been much debated, with popular hypotheses including the influence of mating system and social organisation via sexual selection, dietary niche divergence, and the role of body size (Renschs rule). Here, we investigate the macroevolutionary origins and maintenance of SSD among mammals, using phylogenetic general mixed linear models and a comprehensive global dataset to evaluate correlations of diet, body mass, seasonality, social organisation, and mating system with SSD type. We find that SSD as a whole is lost at a greater rate than it is gained, with female-biased SSD being particularly unstable. Non-monogamy, vertebrate prey consumption, and temperature seasonality correlate with male-biased SSD, while polyandry correlates with female-biased SSD, and both types of SSD are positively correlated with body mass. This is in partial contrast to the predictions of Renschs rule, which predicts that female-biased SSD would correlate negatively with body size. Taken together, our results highlight the importance of considering multiple ecological and social drivers when evaluating the macroevolutionary trajectory of sex differences in body size.

evolutionary biology↗

bioRxiv2023

Bird wings are shaped by thermoregulatory demand for heat dissipation

The tendency for animals in warmer climates to be longer-limbed (Allens Rule) is widely attributed to the demands of thermoregulation. However, the underlying mechanism remains unclear, because variation in limb-length can typically be driven by selection for both efficient heat retention and increased heat dissipation capacity. Using comparative phylogenetic models, we find that occurrence in warmer climates is associated with longer wing bones for 1,520 species of passerine birds. The highly vascularized musculature along these bones is only uncovered during flight, when the wings function as the primary site of heat exchange, cooling the organism by dissipating excess heat generated by muscular activity. Conversely, the musculature along the wing bones is insulated by feathering when at rest, playing a negligible role in heat retention, even in colder climates. Given this asymmetry in thermoregulatory roles, we can identify the positive relationship between temperature and wing bone length as a phenotypic gradient shaped by increased demand for heat dissipation in warmer climates. Our findings provide a clear illustration of the mechanism by which global warming can drive spatial and temporal trends in appendage length, and also highlight the role of heat dissipation in reshaping even the most critical features of vertebrate anatomy. Significance StatementAnimals tend to be longer-limbed in warmer climates, but it remains unclear whether this pattern is driven by selection for cold tolerance at low temperatures or efficient heat dissipation at high temperatures. We show that for 1,520 species of passerines, bird wing bones are relatively longer in warmer climates. The vascularized musculature along these bones primarily functions in heat exchange during flight, when the overwhelming thermoregulatory challenge is dissipating heat, suggesting longer wing-bone length is driven by heat dissipation demands. Our findings reveal the pervasive impacts of thermoregulatory demands on even the most important functional traits.

ecology↗

bioRxiv2020

No latitudinal gradients in tempo or mode of morphological evolution in birds

The latitudinal diversity gradient is one of the most striking patterns in nature yet its implications for morphological evolution are poorly understood. In particular, it has been proposed that an increased intensity of species interactions in tropical biota may either promote or constrain trait evolution, but which of these outcomes predominates remains uncertain. Here, we develop tools for fitting phylogenetic models of phenotypic evolution in which the impact of species interactions--namely, competition--can vary across lineages. Deploying these models on a global avian trait dataset to explore differences in trait divergence between tropical and temperate lineages, we find that the effect of latitude on the mode and tempo of morphological evolution is weak and clade- or trait-dependent. Our results indicate that competition does not disproportionately impact morphological evolution in tropical bird families and question the validity of previously reported patterns of slower trait evolution in the tropics.

evolutionary biology↗

bioRxiv2019

The latitudinal gradient in hand-wing-index: global patterns and predictors of wing morphology in birds

An organisms ability to disperse influences many fundamental processes in ecology. However, standardised estimates of dispersal ability are rarely available, and thus the patterns and drivers of broad-scale variation in dispersal ability remain unclear. Here we present a global dataset of avian hand-wing index (HWI), an estimate of wingtip pointedness widely adopted as a proxy for flight efficiency and dispersal in birds. We show that HWI is correlated with geography and ecology across 10,391 (>99 %) bird species, increasing at higher latitudes and in migratory and/or non-territorial species. After controlling for these effects, the strongest predictor of HWI is temperature variability (i.e. seasonality), with secondary effects of diet and habitat type. Our analyses (1) reveal a prominent latitudinal gradient in HWI shaped by ecological and environmental factors, and (2) provide a global index of avian dispersal ability for wider use in community ecology, macroecology, and macroevolution.\n\nStatement of authorshipThe study was conceived by CS and JAT. Data collection was led by JAT, SC, and CS, with contributions from CS, MNC, NA, SEIJ, CV, HEAM, TPB, and SC. CS performed the analyses. CS and JAT wrote the manuscript and all authors revised the text.

evolutionary biology↗

bioRxiv2019

Ecology, phylogeny, and the evolution of developmental duration in birds

The duration of the developmental period represents a fundamental axis of life history variation in animals, yet broad insights regarding the drivers of this diversity are currently lacking. Here using embryological data combined with information on incubation and fledging periods for 3096 species, we test key mechanistic and adaptive explanations for the evolutionary diversification of developmental durations in birds. First, using data on embryonic development for 20 model species, we show that developmental phases associated primarily with growth are longer and more variable than earlier phases, consistent with a role for allometric constraint in determining the duration of development. Second, using phylogenetic comparative methods, we find that avian developmental durations retain a strong imprint of deep evolutionary history, and that after accounting for these effects, body size differences among species explain less variation (5-22%) in developmental period lengths than previously thought. Finally, by collecting data for a suite of potential explanatory variables, our analyses reveal broad-scale ecological correlates of developmental durations, including variables associated with the relative safety of the developmental environment (e.g. nest height, insularity) and pressures of breeding phenology (e.g. migration). Overall, our results reveal that the combined effects of species body size, ecology, and phylogenetic history can account for 62-93% of the variation in developmental durations across birds, providing broad-scale quantitative insight into the relative importance of mechanistic constraints, adaptive evolution and evolutionary constraints in shaping the diversification of this key life-history trait.

evolutionary biology↗