Biology subjects

Coulson, T.

Publications and source records attributed to Coulson, T..

6 recordsLinked to original sources

bioRxiv2018

Demographic determinants of biometric heritability

The response of quantitative characters to selection depends on their transmission from parents to offspring. A common estimate of this transmission is the biometric heritability defined as the slope of the regression of offspring phenotype on same-aged mid-parent phenotype (i.e. the ratio of the phenotypic parent-offspring covariance over the parental phenotypic variance). This slope is often interpreted as the percentage of phenotypic variation due to additive genetic effects after accounting for confounding factors such as environment, litter or parental effects. However, researchers seldom account for the possible influence of selection on this estimate. Here we study the effect on biometric heritability of fertility and viability selection, as well as phenotype ontogeny (growth) and inheritance from parents to offspring. We present exact formulas for the elasticities of biometric heritability in age-phenotype-structured integral projection models (IPMs), and illustrate these for two iteroparous long-lived species. We find that both viability and fertility selection can strongly affect heritability, mediated by growth and inheritance. Generally, demographic processes that result in parents reproducing at large phenotypes, regardless of their own birth phenotype, decrease heritability. Analysed at equilibrium, our models imply that a heritable character can show no response to selection, if parental phenotypes affect offspring phenotypes and if phenotypes develop with age. Our results further highlight the importance of accounting for demographic processes when estimating heritability.

ecology↗

bioRxiv2018

Experimental manipulation of nocturnal nest cavity temperature in wild blue tits

Advances in the timing of reproduction in temperate species are some of the most well documented biotic responses to increasing global temperatures. However, the magnitude and rate of these advances in timing are not equal across all taxonomic groups. These differences can lead to disruption of interspecific relationships if species respond differently to temperature changes. Understanding the relationship between temperature and phenology is a key step in predicting future population trends for species living in seasonal environments. However, experimentally manipulating temperature in the wild is logistically challenging and has consequently rarely been attempted. In this study we experimentally test whether in-nest temperatures in early spring act as a cue for breeding phenology in a population of wild blue tits (Cyanistes caeruleus). We split nests into three treatments; heated, cooled, and control. In-nest temperature in the heated and cooled boxes was manipulated by an average of {+/-} 0.6 {degrees}C from control temperatures using heating devices and ice packs respectively. We assessed the impact of our experimental manipulation on box occupancy and reproductive timing. We found trends towards earlier phenology in heated nest boxes in addition to a higher occupancy rate in cooled boxes, however neither of these trends was found to be statistically significant. Our ability to distinguish statistical signals was hampered by unexpectedly low occupancy rates across all experimental treatments. Based on the results we cannot say if nocturnal in-nest temperature is an important cue for nest box choice or the timing of laying.

ecology↗

bioRxiv2017

Limited evidence for proactive and reactive spatial responses of prey to an active predator

O_LIThe extent to which prey space use actively minimises predation risk continues to ignite controversy. Methodological reasons that have hindered consensus include inconsistent measurements of predation risk, biased spatiotemporal scales at which responses are measured, and lack of robust null expectations.\nC_LIO_LIWe addressed all three challenges in a comprehensive analysis of the spatiotemporal responses of adult female elk (Cervus elaphus) to the risk of predation by grey wolves (Canis lupus) during winter in northern Yellowstone, USA.\nC_LIO_LIWe quantified spatial overlap between the winter home ranges of GPS-collared elk and three measures of predation risk: the intensity of wolf space use, the distribution of wolf-killed elk and vegetation openness. We also assessed whether elk varied their use of areas characterised by more or less predation risk across hours of the day, and estimated encounter rates between simultaneous elk and wolf pack trajectories. We determined whether observed values were significantly lower than expected if elk movements were random with reference to predation risk using a null model approach.\nC_LIO_LIAlthough a small proportion of elk did show a tendency to minimise use of open vegetation at specific times of the day, overall we highlight a notable absence of spatiotemporal response by female elk to the risk of predation posed by wolves in northern Yellowstone.\nC_LIO_LIOur results suggest that predator-prey interactions may not always result in strong spatiotemporal patterns of avoidance.\nC_LI

ecology↗

bioRxiv2017

Predicting The Evolutionary Consequences Of Trophy Hunting On A Quantitative Trait

Some ecologists suggest that trophy hunting (e.g. harvesting males with a desirable trait above a certain size) can lead to rapid phenotypic change, which has led to an ongoing discussion about evolutionary consequences of trophy hunting. Claims of rapid evolution come from the statistical analyses of data, with no examination of whether these results are theoretically plausible. We constructed simple quantitative genetic models to explore how a range of hunting scenarios affects the evolution of a trophy such as horn length. We show that trophy hunting does lead to trophy evolution defined as change in the mean breeding value of the trait. However, the fastest rates of phenotypic change attributable to trophy hunting via evolution that are theoretically possible under standard assumptions of quantitative genetics are 1 to 2 orders of magnitude slower than the fastest rates reported from statistical analyses. Our work suggests a re-evaluation of the likely evolutionary consequences of trophy hunting would be appropriate when setting policy. Our work does not consider the ethical or ecological consequences of trophy hunting.

evolutionary biology↗

bioRxiv2017

PREDICTING COEXISTENCE IN SPECIES WITH CONTINUOUS ONTOGENETIC NICHE SHIFTS AND COMPETITIVE ASYMMETRY

A longstanding problem in ecology is whether structured life cycles impede or facilitate coexistence between species. Theory based on populations with two discrete stages in the life-cycle indicates that coexistence requires at least one species to shift its niche between stages and that each species is a better competitor in one of the niches. However, in many cases, niche shifts are associated with changes in an underlying continuous trait like organism size and we have few predictions for how the conditions for coexistence are affected by this type of ontogenetic dynamics. Here we develop a framework for analyzing species coexistence based on Integral Projection Models (IPMs) that incorporates continuous ontogenetic changes in both the resource niche and competitive ability. We parameterize the model using experimental data from Trinidadian guppies and make predictions about how niche shifts and competitive symmetries allow or prevent species coexistence. Overall, our results show that the effects of competition on fitness depend upon trait-mediated niche-separation, trait-mediated competitive asymmetry in the part of the niche that is shared across body sizes, and the sensitivity of fitness to body size. When all three conditions are considered, we find multiple ecological and evolutionary routes to coexistence. When both species can shift their niche with increasing body size and competition for resources among the species and sizes is symmetric, then the species that shifts its niche to a greater degree with ontogeny will competitively exclude the other species. When competitive ability increases with increasing body size, then the two species can coexist when the better competitor shifts its niche with body size to a lesser degree than the weaker competitior. This region of coexistence shrinks as the better competitor increasingly shifts its niche with increasing size. When both species shift their niches with size, but each is a better competitor on resources used by smaller or larger individuals, then the model predicts an alternative stable state over some range of niche shifts. We discuss how our results provide new insights into species coexistence and the evolutionary consequences of size-structured interspecific competition.

ecology↗

bioRxiv2016

Adaptive and Non-adaptive Responses of Populations to Environmental Change

Understanding how the natural world will be impacted by environmental change over the coming decades is one of the most pressing challenges facing humanity. Addressing this challenge is difficult because environmental change can generate both population level plastic and evolutionary responses, with plastic responses being either adaptive or non-adaptive. We develop an approach that links quantitative genetic theory with data-driven structured models to allow prediction of population responses to environmental change via plasticity and adaptive evolution. After introducing general new theory, we construct a number of example models to demonstrate that evolutionary responses to environmental change over the short-term will be considerably slower than plastic responses, and that the rate of adaptive evolution to a new environment depends upon whether plastic responses are adaptive or non-adaptive. Parameterization of the models we develop requires information on genetic and phenotypic variation and demography that will not always be available, meaning that simpler models will often be required to predict responses to environmental change. We consequently develop a method to examine whether the full machinery of the evolutionarily explicit models we develop will be needed to predict responses to environmental change, or whether simpler non-evolutionary models that are now widely constructed may be sufficient.

evolutionary biology↗