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676 results for “population density”
FIGURE 1 in Egg Number Varies With Population Density; A Study Of Three Oribatid Mite Species In Orchard Habitats In Egypt
FIGURE 1: Map of Al-Gharbia Governate in Egypt, indicating the three sampling areas (Tanta, Al Mahalla Al Kobra and Kafr Al Zayat). The inset shows the location of Al-Gharbia in Egypt. In each area, three orchards were sampled four times in a year. The same three types of orchard were selected in each area. The distance between locations varies from 19 to 38 km; the distance between sites within one location is 1-2 km.
FIGURE 3 in Egg Number Varies With Population Density; A Study Of Three Oribatid Mite Species In Orchard Habitats In Egypt
FIGURE 3: Relationship between population density and fecundity of the three studied species. The data (pooled over three samples per site) are for all sites, vegetation types and seasons together.
Figure 4 in Effects of Aculus schlechtendali (Acari: Eriophyidae) population densities on Golden Delicious apple production
Figure 4 Regression lines, data points, equations and R2 for the following response variables: A
Data for: Ectoparasite population dynamics affected by host body size but not host density or water temperature in a 32-year long time series
<p>Host density, host body size, and ambient temperature have all been positively associated with increases in parasite infection. However, the relative importance of these factors in shaping long-term parasite population dynamics in wild host populations is unknown due to the absence of long-term studies. Here, we examine long-term drivers of gill lice (Copepoda) infections in Arctic charr (Salmonidae) over 32 years. We predicted that host density and body size and water temperature would all positively affect parasite population size and population growth rate. Our results show that fish size was the main driver of gill lice infections in Arctic charr. In addition, Arctic charr became infected at smaller sizes and with more parasites in years of higher brown trout population size. Negative intraguild interactions between brown trout and Arctic charr appear to drive smaller Arctic charr to seek refuge in deeper areas of the lake, thus increasing infection risk. There was no effect of host density on the force of infection, and the relationship between Arctic charr density and parasite mean abundance was negative, possibly due to an encounter-dilution effect. The population densities of host and parasite fluctuated independently of one another. Water temperature had negligible effects on the temporal dynamics of the gill lice population. Understanding long-term drivers of parasite population dynamics is key for research and management. In fish farms, artificially high densities of hosts lead to vast increases in the transmission of parasitic copepods. However, in wild fish populations fluctuating at natural densities, the surface area available for copepodid attachment might be more important than the density of available hosts.</p>
Population regulation and density‐dependent demography in the Trinidadian guppy
<p>Classic theory for density-dependent selection for delayed maturation requires that a population be regulated through some combination of adult fecundity and/or juvenile survival. We tested whether those demographic conditions were met in four experimental populations of Trinidadian guppies in which delayed maturation of males evolved when the densities of those populations became high. We used monthly mark-recapture data to examine population dynamics and demography in these populations. Three of the four populations displayed clear evidence of regulation. In all four populations, monthly adult survival rates were independent of biomass density or actually increased with increased biomass density. Juvenile recruitment, which is a combination of adult fecundity and juvenile survival, decreased as biomass density increased in all four populations. Demography showed marked seasonality, with greater survival and higher recruitment in the dry season than the wet season. Population regulation via juvenile recruitment supports the hypothesis that density-dependent selection was responsible for the evolution of delayed maturity in males. This body of work represents one of the few complete tests of density-dependent selection theory.</p>
High population density and large body mass lead to increased reproductive success
<p>Although population density and phenotype are known to alter the mating strategies of individuals, their impacts on reproductive success have not been fully investigated. We examined genetic mating system variation (number of mating partners), reproductive success (offspring number) and sperm competition intensity (sires per litter) in semi-natural populations of Brandt's voles (<em>Lasiopodomys brandtii</em>) under low-, medium- and high-densities. We used 12 microsatellite genetic markers and parentage assignment of 3,516 voles, with the aim of identifying the number of mating partners and offspring produced by founder individuals. We provided strong evidence that individuals with more mating partners experienced increased reproductive success, as measured by the production of more offspring, compared with individuals that had fewer mating partners. Further, we found that large males had more mating partners (especially in high-population density enclosures) and also produced more offspring relative to smaller males. A high density of founder individuals led to more sires per litter but greater paternity share across litters (reduced paternity skew). Our results suggest that a polygamous mating system and increased body size should be favored by natural selection, and density-dependent variation in mating strategy would be sufficient to stabilize reproductive fitness under unfavorable conditions such as high founding density.</p>
Density dependence of seed dispersal and fecundity profoundly alters the spread dynamics of plant populations
<ol> <li>Plant population spread has fundamental ecological and evolutionary importance. Both determinants of plant population spread, fecundity and dispersal, can be density-dependent, which should cause feedback between population densities and spread dynamics. Yet it is poorly understood how density-dependence affects key characteristics of spread: spread rate at which the location of the furthest forward individual moves, edge depth (the geographical area over which individuals contribute to spread) and population continuity (occupancy of the spreading population).</li> <li>We present a general modelling framework for analysing the effects of density-dependent fecundity and dispersal on population spread and parameterize this framework with experimental data from a common-garden experiment using five wind-dispersed plant species grown at different densities. </li> <li>Our model shows that density-dependent fecundity and dispersal strongly affect all three population spread characteristics for both exponential and lognormal dispersal kernels. Spread rate and edge depth are strongly correlated but show weaker correlations with population continuity. Positive density-dependence of fecundity increases all three spread characteristics. Increasingly positive density-dependence of dispersal increases spread rate and edge depth but generally decreases population continuity. Density-dependent fecundity and dispersal are largely additive in their effect on spread characteristics. For population continuity, the joint effects of density-dependent fecundity and dispersal are somewhat contingent on the dispersal kernel.</li> <li>The common-garden experiment and the experimentally parameterized mechanistic dispersal model revealed density-dependent fecundity and dispersal across study species. All study species exhibited negative density-dependent fecundity, but they differed qualitatively in the density-dependence of dispersal distance and probability of long-distance dispersal. The negative density-dependence of fecundity and dispersal found for three species reinforced each other in reducing spread rate and edge depth. The positively density-dependent dispersal found for two species markedly increased spread rate and edge depth. Population continuity was hardly affected by population density in all study species except Crepis sancta in which it was strongly reduced by negatively density-dependent fecundity.</li> <li> <em>Synthesis</em>. Density-dependent fecundity and seed dispersal profoundly alter population spread. In particular, positively density-dependent dispersal should promote the spread and genetic diversity of plant populations migrating under climate change but also complicate the control of invasive species.</li> </ol>
A Great Escape: resource availability and density-dependence shape population dynamics along trailing range edges
<p>Populations along geographical range limits are often exposed to unsuitable climate and low resource availability relative to core populations. As such, there has been a renewed focus on understanding the factors that determine range limits to better predict how species will respond to global change. Using recent theory on range limits and classical understanding of density dependence, we evaluated the influence of resource availability on the snowshoe hare Lepus americanus along its trailing range edge. We estimated variation in population density, habitat use, survival, and parasite loads to test the Great Escape Hypothesis (GEH), i.e. that density dependence determines, in part, a species' persistence along trailing edges. We found that variability in resource availability affected density and population fluctuations and led to trade-offs in survival for snowshoe hare populations in the northeastern USA. Hares living in resource-limited environments had lower and less variable population density, yet higher survival and lower parasitism compared to populations living in resource-rich environments. We suggest that density-dependent dynamics, elicited by resource availability, provide hares a unique survival advantage and partly explain persistence along their trailing edge. We hypothesize that this low-density escape from predation and parasitism occurs for other prey species along trailing edges, but the extent to which it occurs is likely conditional on the quality of matrix habitat. Our work indicates that biotic factors play an important role in shaping species' trailing edges and more detailed examination of non-climatic factors is warranted to better inform conservation and management decisions.</p>
Dataset for density estimation for an island population of raccoon dogs in Japan
<p><span>Estimation of the population</span><span> size</span><span> is essential for understanding population dynamics</span><span>. Estimating animal density using multiple methods and/or multiple attempts is required for accurate estimations. Raccoon dog (<em>Nyctereutes</em> <em>procyonoides</em>) is native to East Asia, including Japan, and has become an invasive species in Europe. Information on raccoon dog density in their native range is important to understand their invasion; however, relatively few studies have been conducted on raccoon dog density in their native range. In this study, we extracted DNA from fecal samples of raccoon dogs inhabiting a small island in Japan and conducted density estimation over two periods using DNA capture-recapture methods: CAPWIRE and SECR. We also investigated sex ratio</span> <span>using genetic sex identification. Density estimates using SECR were approximately threefold different between the two study periods: </span><span>17.2</span><span> individuals per km<sup>2</sup> in 2018 and </span><span>49.0 </span><span>individuals per km<sup>2</sup> in 2020. In contrast, estimates using CAPWIRE were relatively stable: </span><span>21.7</span><span> individuals per km<sup>2</sup> in 2018 and </span><span>24.3</span><span> individuals per km<sup>2</sup> in 2020. A drastic increase or decrease is not expected during the study period, and thus</span><span>, density estimates using CAPWIRE are more reasonable than </span><span>those using SECR. The small number of samples per individual might result in low accuracy of density estimates by SECR. The density estimated by CAPWIRE was similar to that in the main island in Japan</span> <span>and higher than that in Europe. Feeding competition with other omnivorous carnivores and/or predation risk by wolves might maintain the low density in Europe. The sex ratio of raccoon dogs was 1:1, which was similar to </span><span>the values in invasive raccoon dogs and </span><span>other canids. Further genetic census</span><span>, including sex identification in various landscapes in their native and invasive range, will enable us to understand not only the ecology of raccoon dogs but also their adaptations to </span><span>their invading areas.</span></p>
Data from: Evaluating predator control using two non-invasive population metrics: a camera trap activity index and density estimation from scat genotyping
<p>Includes datasets from the Wimmera and Mallee, Victoria, Australia:</p> <p>- Fox camera trap data used to model activity</p> <p>- Fox scat SECR capture and trap files used to model density</p>
The effects of human population density on trophic interactions are contingent upon latitude
<p><em>Aim: </em>Studies conducted at a global scale are necessary to make general conclusions on the effect of urbanization on trophic interactions and explore how these effects change along latitudinal gradients. Since biotic interactions are more intense at lower latitudes, we predict they are less likely to be affected by human impacts than at higher latitudes. Therefore, we test the hypothesis that the effect of urbanization (quantified by human population density) on trophic interactions, specifically insect herbivory and bird predation, decreases with an increase in latitude</p> <p><em>Location: </em>Global (881 study sties)</p> <p><em>Time period</em>: 2000-2021</p> <p><em>Major taxa studied:</em> Birds, arthropods and plants.</p> <p><em>Methods:</em> We compiled global data on insect herbivory and bird predation from individual studies using similar methodologies, and fitted generalized linear mixed models to test the effect of human population density, latitude and their interaction on these two response variables.</p> <p><em>Results: </em>The intensity of herbivory and predation decreased with the increase of human population density at lower latitudes, remained unaffected at intermediate latitudes, and increased at higher latitudes.</p> <p><em>Main conclusions: </em>The effect of urbanization on the intensities of trophic interactions varies across latitudes, with a reversal of the pattern at high vs. low latitudes potentially explained by the urban heat island effect, being this pattern consistent across the two main trophic interaction.</p>
More people, more cats, more parasites: Human population density and temperature variation predict the prevalence of Toxoplasma gondii oocyst shedding in free-ranging domestic and wild felids
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Population structure of five native sheep breeds of Sweden estimated with high density SNP genotypes
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Spatial variation in population-density, movement and detectability of snow leopards in a multiple use landscape in Spiti Valley, Trans-Himalaya
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Fecal standing crop with real time correction using scat detection dogs to estimate population density
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High population density and large body mass lead to increased reproductive success
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Dataset for density estimation for an island population of raccoon dogs in Japan
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Simulated genotype data from: Effective population size estimation in large marine populations: Considering current challenges and opportunities when simulating large datasets with high-density genomic information
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Data from: Density-independent predation affects migrants and residents equally in a declining partially migratory elk population
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Counterintuitive scaling between population abundance and local density: implications for modelling transmission of infectious diseases in bat populations
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Allen Brain Atlas
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