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The Journal of Animal Ecology Jan 2018Insular species are predicted to broaden their niches, in response to having fewer competitors. They can thus exploit a greater proportion of the resource spectrum. In...
Insular species are predicted to broaden their niches, in response to having fewer competitors. They can thus exploit a greater proportion of the resource spectrum. In turn, broader niches are hypothesized to facilitate (or be a consequence of) increased population densities. We tested whether insular lizards have broader dietary niches than mainland species, how it relates to competitor and predator richness, and the nature of the relationship between population density and dietary niche breadth. We collected population density and dietary niche breadth data for 36 insular and 59 mainland lizard species, and estimated competitor and predator richness at the localities where diet data were collected. We estimated dietary niche shift by comparing island species to their mainland relatives. We controlled for phylogenetic relatedness, body mass and the size of the plots over which densities were estimated. We found that island and mainland species had similar niche breadths. Dietary niche breadth was unrelated to competitor and predator richness, on both islands and the mainland. Population density was unrelated to dietary niche breadth across island and mainland populations. Our results indicate that dietary generalism is not an effective way of increasing population density nor is it result of lower competitive pressure. A lower variety of resources on islands may prevent insular animals from increasing their niche breadths even in the face of few competitors.
Topics: Animals; Diet; Geography; Islands; Lizards; Phylogeny; Population Density; Predatory Behavior
PubMed: 28944457
DOI: 10.1111/1365-2656.12762 -
International Journal of Environmental... Nov 2021Urban population density distribution contributes towards a deeper understanding of peoples' activities patterns and urban vibrancy. The associations between the...
Urban population density distribution contributes towards a deeper understanding of peoples' activities patterns and urban vibrancy. The associations between the distribution of urban population density and land use are crucial to improve urban spatial structure. Despite numerous studies on population density distribution and land use, the significance of spatial dependence has attained less attention. Based on the Baidu heat map data and points of interests data in the main urban zone of Guangzhou, China, the current paper first investigated the spatial evolution and temporal distribution characteristics of urban population density and examined the spatial spillover influence of land use on it through spatial correlation analysis methods and the spatial Durbin model. The results show that the urban population density distribution is characterized by aggregation in general and varies on weekends and weekdays. The changes in population density within a day present a trend of "rapid growth-gentle decline-rapid growth-rapid decline". Furthermore, the spatial spillover effects of land use exist and play the same important roles in population density distribution as the direct effects. Additionally, different types of land use show diverse direct effects and spatial spillover effects at various times. These findings suggest that balancing the population density distribution should consider the indirect effect from neighboring areas, which hopefully provide implications for urban planners and policy makers in utilizing the rational allocation of public resources and regarding optimization of urban spatial structure.
Topics: China; Cities; Humans; Population Density; Spatial Analysis; Urban Population; Urbanization
PubMed: 34831916
DOI: 10.3390/ijerph182212160 -
Ecology Letters Apr 2019We address two fundamental ecological questions: what are the limits to animal population density and what determines those limits? We develop simple alternative models...
We address two fundamental ecological questions: what are the limits to animal population density and what determines those limits? We develop simple alternative models to predict population limits in relation to body mass. A model assuming that within-species area use increases with the square of daily travel distance broadly predicts the scaling of empirical extremes of minimum density across birds and mammals. Consistent with model predictions, the estimated density range for a given mass, 'population scope', is greater for birds than for mammals. However, unlike mammals and carnivorous birds, expected broad relationships between body mass and density extremes are not supported by data on herbivorous and omnivorous birds. Our results suggest that simple constraints on mobility and energy use/supply are major determinants of the scaling of density limits, but further understanding of interactions between dietary constraints and density limits are needed to predict future wildlife population responses to anthropogenic threats.
Topics: Animals; Birds; Carnivora; Mammals; Models, Biological; Population Density
PubMed: 30724435
DOI: 10.1111/ele.13227 -
The Journal of Animal Ecology Aug 2019Numerous studies have demonstrated that dispersal is dependent on both disperser phenotype and the local environment. However, there is substantial variability in the...
Numerous studies have demonstrated that dispersal is dependent on both disperser phenotype and the local environment. However, there is substantial variability in the observed strength and direction of phenotype- and environment-dependent dispersal. This has been hypothesized to be the result of interactive effects among the multiple phenotypic and environmental factors that influence dispersal. Here, our goal was to test the hypothesis that these interactions are responsible for generating variation in dispersal behaviour. We achieved these goals by conducting a large, 2-year, mark-release-recapture study of the backswimmer Notonecta undulata in an array of 36 semi-natural ponds. We measured the effects of multiple phenotypic (sex and body size) and environmental (population density and sex ratio) factors, on both dispersal probability and dispersal distance. We found support for the hypothesis that interactive effects influence dispersal and produce variability in phenotype- and environment-dependent dispersal: dispersal probability was dependent on the three-way interaction between sex, body mass and population density. Small males displayed strong, positive density dependence in their dispersal behaviour, while large males and females overall did not respond strongly to density. Small notonectids, regardless of sex, were more likely to disperse, but this effect was strongest at high population densities. Finally, the distance dispersed by backswimmers was a negative function of population density, a pattern which we hypothesize could be related to: (a) individuals from high and low density patches having different dispersal strategies, or (b) the effect of density on dispersal capacity. These results suggest that phenotype-by-environment interactions strongly influence dispersal. Since phenotype- and environment-dependent dispersal has different consequences for ecological and evolutionary dynamics (e.g. metapopulation persistence and local adaptation) than random dispersal, interactive effects may have wide-reaching impacts on populations and communities. We therefore argue that more investment should be made into estimating the effects of multiple, interacting factors on dispersal and determining whether similar interactive effects are acting across systems.
Topics: Animals; Biological Evolution; Ecology; Female; Gene-Environment Interaction; Male; Phenotype; Population Density; Population Dynamics
PubMed: 31077361
DOI: 10.1111/1365-2656.13008 -
The Journal of Animal Ecology Apr 2021Nearly 100 years ago, Charles Elton described lemming and vole population cycles as ecological models for understanding population regulation in nature. Yet, the...
Nearly 100 years ago, Charles Elton described lemming and vole population cycles as ecological models for understanding population regulation in nature. Yet, the mechanisms driving these cycles are still not fully understood. These rodent populations can continue to cycle in the absence of predation and with food supplementation, and represent a major unsolved problem in population ecology. It has been hypothesized that the social environment at high population density can drive selection for a low-reproduction phenotype, resulting in population self-regulation as an intrinsic mechanism driving the cycles. However, a physiological mechanism for this self-regulation has not been demonstrated. We manipulated population density in wild meadow voles Microtus pennsylvanicus using large-scale field enclosures over 3 years and examined reproductive performance and physiology. Within the field enclosures, we assessed the proportion of breeding animals, mass at sexual maturation, and faecal androgen and oestrogen metabolites. We then collected brain tissue from juvenile voles born at high or low density, quantified mRNA expression of gonadotropin-releasing hormone (GnRH) and oestrogen receptor alpha (ERα) and measured DNA methylation at six CpG sites in a region that was highly conserved with the mouse GnRH promoter. At high density, there was a lower proportion of reproductive animals. Juvenile voles born at high densities had reduced expression of GnRH in the hypothalamus, accompanied by marginally lower faecal sex hormone metabolites. Female juvenile voles born at high density also had higher methylation levels at two CpG sites while males did not, aligning with prior observations that females (but not males) from high-density environments retain reduced reproduction long term. Our results support a physiological basis for population self-regulation in vole cycles, as altering population density alone induced reproductive downregulation at the hypothalamic level. Our results demonstrate that altering the early-life social environment can fundamentally impact reproductive function in the brain. This, in turn, can drive population demography changes in wild animals.
Topics: Animals; Arvicolinae; Female; Gonadotropin-Releasing Hormone; Male; Mice; Population Density; Reproduction; Self-Control
PubMed: 33550586
DOI: 10.1111/1365-2656.13430 -
Systematic Biology Aug 2022Balance indices that quantify the symmetry of branching events and the compactness of trees are widely used to compare evolutionary processes or tree-generating...
Balance indices that quantify the symmetry of branching events and the compactness of trees are widely used to compare evolutionary processes or tree-generating algorithms. Yet, existing indices are not defined for all rooted trees, are unreliable for comparing trees with different numbers of leaves, and are sensitive to the presence or absence of rare types. The contributions of this article are twofold. First, we define a new class of robust, universal tree balance indices. These indices take a form similar to Colless' index but can account for population sizes, are defined for trees with any degree distribution, and enable meaningful comparison of trees with different numbers of leaves. Second, we show that for bifurcating and all other full m-ary cladograms (in which every internal node has the same out-degree), one such Colless-like index is equivalent to the normalized reciprocal of Sackin's index. Hence, we both unify and generalize the two most popular existing tree balance indices. Our indices are intrinsically normalized and can be computed in linear time. We conclude that these more widely applicable indices have the potential to supersede those in current use. [Cancer; clone tree; Colless index; Sackin index; species tree; tree balance.].
Topics: Algorithms; Biological Evolution; Phylogeny; Population Density
PubMed: 35412638
DOI: 10.1093/sysbio/syac027 -
Ecology Letters Nov 2019Species simultaneously compete with and facilitate one another. Size can mediate transitions along this competition-facilitation continuum, but the consequences for...
Species simultaneously compete with and facilitate one another. Size can mediate transitions along this competition-facilitation continuum, but the consequences for demography are unclear. We orthogonally manipulated the size of a focal species, and the size and density of a heterospecific neighbour, in the field using a model marine system. We then parameterised a size-structured population model with our experimental data. We found that heterospecific size and density interactively altered the population dynamics of the focal species. Size determined whether heterospecifics facilitated (when small) or competed with (when large) the focal species, while density strengthened these interactions. Such size-mediated interactions also altered the pace of the focal's life history. We provide the first demonstration that size and density mediate competition and facilitation from a population dynamical perspective. We suspect such effects are ubiquitous, but currently underappreciated. We reiterate classic cautions against inferences about competitive hierarchies made in the absence of size-specific data.
Topics: Models, Biological; Population Density; Population Dynamics
PubMed: 31468661
DOI: 10.1111/ele.13381 -
Scientific Reports Apr 2022The time period between 560 and 360 ka (MIS14 to MIS11) was critical for the evolution of the Neanderthal lineage and the appearance of Levallois technology in Europe....
The time period between 560 and 360 ka (MIS14 to MIS11) was critical for the evolution of the Neanderthal lineage and the appearance of Levallois technology in Europe. The shifts in the distribution of the human populations, driven by cyclical climate changes, are generally accepted to have played major roles in both processes. We used a dataset of palaeoclimate maps and a species distribution model to reconstruct the changes in the area of Western Europe with suitable environmental conditions for humans during 11 time intervals of the MIS14 to MIS 11 period. Eventually, the maximum sustainable human population within the suitable area during each time interval was estimated by extrapolating the relationship observed between recent hunter-gatherer population density and net primary productivity and applying it to the past. Contrary to common assumptions, our results showed the three Mediterranean Peninsulas were not the only region suitable for humans during the glacial periods. The estimated total sustainable population of Western Europe from MIS14 to MIS11 oscillated between 13,000 and 25,000 individuals. These results offer a new theoretical scenario to develop models and hypotheses to explain cultural and biological evolution during the Middle Pleistocene in Western Europe.
Topics: Animals; Climate Change; Europe; Hominidae; Humans; Neanderthals; Population Density
PubMed: 35484382
DOI: 10.1038/s41598-022-10642-w -
Genome Biology and Evolution Jul 2022We discuss the genetic, demographic, and selective forces that are likely to be at play in restricting observed levels of DNA sequence variation in natural populations...
We discuss the genetic, demographic, and selective forces that are likely to be at play in restricting observed levels of DNA sequence variation in natural populations to a much smaller range of values than would be expected from the distribution of census population sizes alone-Lewontin's Paradox. While several processes that have previously been strongly emphasized must be involved, including the effects of direct selection and genetic hitchhiking, it seems unlikely that they are sufficient to explain this observation without contributions from other factors. We highlight a potentially important role for the less-appreciated contribution of population size change; specifically, the likelihood that many species and populations may be quite far from reaching the relatively high equilibrium diversity values that would be expected given their current census sizes.
Topics: Genetic Variation; Genetics, Population; Models, Genetic; Population Density; Selection, Genetic
PubMed: 35738021
DOI: 10.1093/gbe/evac096 -
Health & Place May 2023Population density is an indicator in many studies, but often with only a cursory explanation of why. Unfortunately, elected officials and the media draw misleading...
Population density is an indicator in many studies, but often with only a cursory explanation of why. Unfortunately, elected officials and the media draw misleading conclusions about population density and public health. After providing three reasons why population density is linked to human health outcomes, using state, county, municipal and neighborhood scale data, we show that population density serves as a surrogate for explaining the geographical distribution of life expectancy and broadband access. However, population density loses its unique contribution when other factors influencing health are included. We urge authors to explain why they include population density in their studies.
Topics: Humans; Population Density; Life Expectancy; Residence Characteristics
PubMed: 36947902
DOI: 10.1016/j.healthplace.2023.103001