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22 results for “density dependent dispersal”
Intersexual differences in density-dependent dispersal and their evolutionary drivers
Dispersal is well recognised as a major driver of evolutionary processes in local populations. Nevertheless, dispersal abilities should also be perceived as a life history trait, being subject to evolutionary changes in response to various drivers. Empirical studies investigating these drivers rarely consider that they may influence male and female dispersal differently. The purpose of our study was to document intersexual differences in density-dependent emigration from local habitat patches. As a model system we used a metapopulation of Maculinea (Phengaris) teleius butterfly, in which densities of both sexes vary greatly throughout the flying season. Following intensive mark-release-recapture surveys, the parameters and predictors of dispersal were analysed with the Virtual Migration model and the multi-state recapture model. The emigration rate in males was substantially higher in the early season, especially at smaller habitat patches. With the proportion of females increasing with the season progression, males became reluctant to emigrate from their natal patches. In turn, higher female emigration in the later part of the season was most strongly associated with female tendency to reduce intraspecific competition experienced by their offspring. Our findings provide evidence for the impact of reproductive strategies on dispersal in both sexes. The difference in reproductive strategies of males and females explain sex-biased dispersal in different parts of the season, which carries important implications for metapopulation functioning.
Impacts of flowering density on pollen dispersal and gametic diversity are scale dependent
<p>Pollen dispersal is a key evolutionary and ecological process, but the degree to which variation in the density of concurrently flowering conspecific plants (i.e., co-flowering density) shapes pollination patterns remains understudied. We monitored co-flowering density and corresponding pollination patterns of the insect-pollinated palm <em>Oenocarpus bataua</em> in northwestern Ecuador and found that the influence of co-flowering density on these patterns was scale-dependent: high neighborhood densities were associated with reductions in pollen dispersal distance and gametic diversity of progeny arrays, whereas we observed the opposite pattern at the landscape scale. In addition, neighborhood co-flowering density also impacted forward pollen dispersal kernel parameters, suggesting that low neighborhood densities encourage pollen movement and may promote gene flow and genetic diversity. Our work reveals how co-flowering density at different spatial scales influences pollen movement, which in turn informs our broader understanding of the mechanisms underlying patterns of genetic diversity and gene flow within populations of plants.</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>
From seed dispersal service to reproductive collapse: density-dependent outcome of a palm-mammal interaction
<p>Interspecific ecological interactions are inherently context-dependent. They may vary in both magnitude and sign depending on the biotic and abiotic conditions, depicting a mutualism-antagonism continuum. However, how population abundances and the activity of interacting species modulate these interactions remains underexplored. Here, we chose the interaction between the Mediterranean palm <em>Chamaerops</em> <em>humilis</em> and the feral goat <em>Capra</em> <em>hircus</em> in Mallorca (Balearic Islands, Spain). We selected three study plots with low, intermediate and high intensities of goat activity where we characterized palm distribution, seed rain, seed predation, and early palm recruitment during two consecutive years. Since goats can cause both costs (e.g. florivory) and benefits (e.g. seed dispersal) to <em>C. humilis</em> performance, we investigated the following three questions: (1) Does the spatial distribution of adult palms vary depending on the intensity of goat activity? (2) Does the intensity of goat activity influence seed rain and its potential spatial association with adult palms? (3) To what extent does the intensity of goat activity determine post-dispersal events such as seed predation and seedling emergence? We found that adult palms showed a more clumped and complex distribution (double-cluster process) in plots with low and intermediate goat activity compared to that with high goat activity (simple-cluster process). In the low goat activity plot, dispersed seeds were spatially aggregated around adult palms, showing twice insect-seed predation and nearly three times lower seed germination success than those in the intermediate goat activity plot. Palm seed dispersal and recruitment were almost nil in the high goat activity plot due to heavy consumption of palm inflorescences and developing fruits by goats. Our findings demonstrate how the net outcome of plant-animal interactions can change from mutualism to antagonism, from reproductive service to reproductive collapse, depending on the abundance and the activity of the interacting species.</p>
Impacts of flowering density on pollen dispersal and gametic diversity are scale dependent
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From seed dispersal service to reproductive collapse: density-dependent outcome of a palm-mammal interaction
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Intersexual differences in density-dependent dispersal and their evolutionary drivers
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Density dependence of seed dispersal and fecundity profoundly alters the spread dynamics of plant populations
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Dispersal evolution diminishes the negative density dependence in dispersal
In many organisms, dispersal varies with the local population density. Such patterns of density-dependent dispersal (DDD) are expected to shape the dynamics, spatial spread and invasiveness of populations. Despite their ecological importance, empirical evidence for the evolution of DDD patterns remains extremely scarce. This is especially relevant because rapid evolution of dispersal traits has now been empirically confirmed in several taxa. Changes in DDD of dispersing populations could help clarify not only the role of DDD in dispersal evolution, but also the possible pattern of subsequent range expansion. Here, we investigate the relationship between dispersal evolution and DDD using a long-term experimental evolution study on Drosophila melanogaster. We compared the DDD patterns of four dispersal-selected populations and their non-selected controls. The control populations showed negative DDD, which was stronger in females than in males. In contrast, the dispersal-selected populations showed density-independent dispersal, where neither males nor females exhibited DDD. We compare our results with previous evolutionary predictions that focused largely on positive DDD, and highlight how the direction of evolutionary change depends on the initial DDD pattern of a population. Finally, we discuss the implications of DDD evolution for spatial ecology and evolution.
Model output data for "Negative density-dependent dispersal emerges from the joint evolution of density- and body condition-dependent dispersal strategies"
<p>Empirical studies have documented both positive and negative density-dependent dispersal, yet most theoretical models predict positive density dependence as a mechanism to avoid competition. Several hypotheses have been proposed to explain the occurrence of negative density-dependent dispersal, but few of these have been formally modeled. Here, we developed an individual based model of the evolution of density-dependent dispersal. This model is novel in that it considers the effects of density on dispersal directly, and indirectly through effects on individual condition. Body condition is determined mechanistically, by having juveniles compete for resources in their natal patch. We found that the evolved dispersal strategy was a steep, increasing function of both density and condition. Interestingly, although populations evolved a positive density-dependent dispersal strategy, the simulated metapopulations exhibited negative density-dependent dispersal. This occurred because of the negative relationship between density and body condition: high density sites produced low condition individuals that lacked the resources required for dispersal. Our model therefore generates the novel hypothesis that observed negative density-dependent dispersal can occur when high density limits the ability of organisms to disperse. We suggest that future studies consider how phenotype is linked to the environment when investigating the evolution of dispersal.</p>
Data from: Density dependence in demography and dispersal generates fluctuating invasion speeds
Density dependence plays an important role in population regulation and is known to generate temporal fluctuations in population density. However, the ways in which density dependence affects spatial population processes, such as species invasions, are less understood. Although classical ecological theory suggests that invasions should advance at a constant speed, empirical work is illuminating the highly variable nature of biological invasions, which often exhibit nonconstant spreading speeds, even in simple, controlled settings. Here, we explore endogenous density dependence as a mechanism for inducing variability in biological invasions with a set of population models that incorporate density dependence in demographic and dispersal parameters. We show that density dependence in demography at low population densities—i.e., an Allee effect—combined with spatiotemporal variability in population density behind the invasion front can produce fluctuations in spreading speed. The density fluctuations behind the front can arise from either overcompensatory population growth or density-dependent dispersal, both of which are common in nature. Our results show that simple rules can generate complex spread dynamics and highlight a source of variability in biological invasions that may aid in ecological forecasting.
Data from: Loss of animal seed dispersal increases extinction risk in a tropical tree species due to pervasive negative density dependence across life stages
Overhunting in tropical forests reduces populations of vertebrate seed dispersers. If reduced seed dispersal has a negative impact on tree population viability, overhunting could lead to altered forest structure and dynamics, including decreased biodiversity. However, empirical data showing decreased animal-dispersed tree abundance in overhunted forests contradict demographic models which predict minimal sensitivity of tree population growth rate to early life stages. One resolution to this discrepancy is that seed dispersal determines spatial aggregation, which could have demographic consequences for all life stages. We tested the impact of dispersal loss on population viability of a tropical tree species, Miliusa horsfieldii, currently dispersed by an intact community of large mammals in a Thai forest. We evaluated the effect of spatial aggregation for all tree life stages, from seeds to adult trees, and constructed simulation models to compare population viability with and without animal-mediated seed dispersal. In simulated populations, disperser loss increased spatial aggregation by fourfold, leading to increased negative density dependence across the life cycle and a 10-fold increase in the probability of extinction. Given that the majority of tree species in tropical forests are animal-dispersed, overhunting will potentially result in forests that are fundamentally different from those existing now.
Data from: Spatio-temporal dynamics of density-dependent dispersal during a population colonisation
Predicting population colonisations requires understanding how spatio-temporal changes in density affect dispersal. Density can inform on fitness prospects, acting as a cue for either habitat quality, or competition over resources. However, when escaping competition, high local density should only increase emigration if lower-density patches are available elsewhere. Few empirical studies on dispersal have considered the effects of density at the local and landscape scale simultaneously. To explore this, we analyze 5 years of individual-based data from an experimental introduction of wild guppies Poecilia reticulata. Natal dispersal showed a decrease in local density dependence as density at the landscape level increased. Landscape density did not affect dispersal among adults, but local density-dependent dispersal switched from negative (conspecific attraction) to positive (conspecific avoidance), as the colonisation progressed. This study demonstrates that densities at various scales interact to determine dispersal, and suggests that dispersal trade-offs differ across life stages.
Data from: Density-dependent dispersal strategy of pollinator moderates the adverse effect of habitat loss on plant reproduction
<p><span>1. </span><span>Major challenges for plant conservation are predicting the effect of habitat loss on pollination success and plant reproduction </span><span>potential</span><span>. Most studies report that pollinator movement is affected by quantitative and spatial characteristics of landscapes. However, little is known about the role of pollinator movement, impacted by floral volatiles and intraspecies interaction, on plant reproduction in fragmented landscapes.</span></p> <p><span>2. </span><span>To clarify the effect of pollinator movement on plant reproduction </span><span>relative to </span><span>habitat loss, we developed an integrated model incorporating pollinator's foraging response with its </span><span>dispersal</span> <span>process mediated by a density-dependent dispersal (DDD) strategy</span><span>.</span> <span>This model</span> <span>performed better in capturing behaviorals response of pollinators than do current methods. The integrated model was verified with field results of pollinator visitation and plant reproduction of saltcedar (<em>Tamarix</em> <em>chinensis</em>) inhabiting the Yellow River Delta, and then was compared against a dispersal strategy called density-independent dispersal (DID). The model was applied to landscapes with various non-habitat percentage (<em>NHP</em>) to explore the effect of habitat loss on plant reproduction.</span></p> <p><span>3. </span><span>Results suggested that saltcedar populations differ in their responses to habitat loss, which depended on the spatial scales considered. At landscape scale, increasing <em>NHP</em> significantly inhibited the dispersion extent of floral volatiles and therefore reduced pollinator visitation and subsequent seed production, especially when <em>NHP</em> exceeded the critical threshold of 0.6.</span> <span>However, at patch scale, comparing with DID strategy, the DDD strategy enabled pollinators to increase their utilization of flowers by 43.42% and 6.79% in low-density and distant plant patches, whereas their utilization was reduced by 7.75% and 2.24% in high-density and central patches, respectively. </span><span>Plant reproduction was improved correspondingly</span> <span>in low-density and distant patches under different <em>NHP</em>s.</span></p> <p><span>4. </span><span>Consequently, habitat loss inhibits the volatiles dispersion and interferes with the foraging success of pollinators, a major factor influencing plant reproduction at landscape scale. At patch scale, adaptive utilization of pollinators exhibiting DDD strategy alleviates the negative effect of habitat loss on plant production and maintains plant population persistence. Since pollinator behavioral response is critical to plant reproduction, we recommend the use of the here-presented integrated model to assess the impact of habitat loss on plant reproduction.</span></p>
Dispersal evolution diminishes the negative density dependence in dispersal
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Model output data for "Negative density-dependent dispersal emerges from the joint evolution of density- and body condition-dependent dispersal strategies"
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Data from: Density dependence in demography and dispersal generates fluctuating invasion speeds
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Data from: Density-dependent fitness, not dispersal movements, drives temporal variation in spatial genetic structure in dark-eyed juncos (Junco hyemalis)
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Data from: Density-dependent dispersal strategy of pollinator moderates the adverse effect of habitat loss on plant reproduction
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Data from: Spatio-temporal dynamics of density-dependent dispersal during a population colonisation
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