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171 results for “density-dependent”
Density-dependence and territorial competitors can modulate parrotfish social foraging and herbivory on coral reefs
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Density-dependent selection and the maintenance of colour polymorphism in barn owls
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Data from: Density-dependence produces spurious relationships among demographic parameters in a harvested species
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Density-dependent natural selection mediates harvest-induced trait changes
<p>Rapid life-history changes caused by size-selective harvesting are often interpreted as a response to direct harvest selection against a large body size. However, similar trait changes may result from a harvest-induced relaxation of natural selection for a large body size via density-dependent selection. Here, we show evidence of such density-dependent selection favouring large-bodied individuals at high population densities, in replicated pond populations of medaka fish. Harvesting, in contrast, selected medaka directly against a large body size and, in parallel, decreased medaka population densities. Five years of harvesting were enough for harvested and unharvested medaka populations to inherit the classically-predicted trait differences, whereby harvested medaka grew slower and matured earlier than unharvested medaka. We demonstrate that this life-history divergence was not driven by direct harvest selection for a smaller body size in harvested populations, but by density-dependent natural selection for a larger body size in unharvested populations.</p>
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.
Data from: Density-dependent adaptive topography in a small passerine bird, the collared flycatcher
<p>The adaptive topography is a central concept in evolutionary biology, describing how the mean fitness of the population changes with gene frequencies or mean phenotypes. We use expected population size as quantity to be maximized by natural selection to show that selection on pairwise combinations of reproductive traits of collared flycatchers caused by fluctuations in population size generated an adaptive topography with distinct peaks often located at intermediate phenotypes. This occurred because <em>r</em>- and <em>K</em>-selection made phenotypes favored at small densities different from those with higher fitness at population sizes close to the carrying capacity <em>K</em>. The fitness decreased rapidly with a delay in the timing of egg-laying with a density-dependent effect especially occurring among early-laying females. The number of fledglings maximizing fitness was larger at small population sizes than close to <em>K</em>. Finally, there was directional selection for large fledglings independent of population size. We suggest that these patterns can be explained by increased competition for some limiting resources or access to favorable nest sites at high population densities. Thus, <em>r</em>- and <em>K</em>-selection based on expected population size as evolutionary maximization criterion may influence life history evolution and constrain the selective responses to changes in the environment.</p>
Density-dependent within-patch movement behavior of two competing species
<p class="MsoNormal">Movement behavior is central to understanding species distributions, population dynamics and coexistence with other species. At present, relatively little is known about how conspecific and interspecific competitor density affect movement behavior. We conducted releases of two species of competing <em>Tribolium</em> flour beetles at different densities, alone and together in homogeneous microcosms, and tested whether their recaptures-with-distance were well described by a random-diffusion model. We also determined whether mean displacement distances varied with the release density of conspecific and heterospecific beetles. A diffusion model provided a good fit to the redistribution of <em>T. castaneum</em> and <em>T. confusum </em>at all release densities, explaining an average of >60% of the variation in recaptures. For both species, mean displacement (directly proportional to the diffusion rate) exhibited a humped-shaped relationship with conspecific density. Finally, we found that both species of beetle impacted the within-patch movement rates of the other species, but it depended on density. For <em>T. castaneum</em> in the highest density treatment, the addition of equal numbers of <em>T. castaneum</em> or <em>T. confusum</em> had the same effect, with mean displacements reduced by approximately one-half. The same result occurred for <em>T. confusum</em> released at an intermediate density. In both cases, it was total beetle abundance, not species identity that mattered to mean displacement. We suggest that displacement or diffusion rates that exhibit a nonlinear relationship with density or depend on the presence or abundance of interacting species should be considered when attempting to predict the spatial spread of populations.</p>
Density-dependent changes of mating system and family structure in Brandt's voles (Lasiopodomys brandtii)
<p>A mating system is an important life history for animals dealing with changing environments. Population density affects the plasticity of a mating system and subsequently the family structure of animals, but its impacts on mating systems and social structures are rarely investigated by using molecular markers in field conditions. In this study, using microsatellite genetic markers, we examined the changes in the social and genetic mating system and family structure of Brandt's voles in the grassland of Inner Mongolia, China, under low-, medium-, and high-density enclosures (each enclosure 0.48-ha with 4 replicates.) We found, that with the increase in population density of the founder voles introduced into the enclosure in early spring, both sexes increased their number of genetic mating partners, while males increased their social partners, resulting in a more promiscuous mating system. The number of genetic fathers and mothers per family, the number of social offspring per founder male or female, and the proportion of extra-group offspring increased with increased density, indicating that the response of the family structure to density change which is consistent with the change in mating system observed in our study. Both male and female voles had multiple mates, but males had a larger number of social and genetic mates, the number of social and genetic offspring, and the number of social and genetic families. Our study highlights the significance of density-dependent plasticity of a mating system and family structure in affecting the population change of small mammals.</p>
Insect root feeders incur negative density-dependent damage across plant species in an alpine meadow
<p>Although herbivores are well known to incur positive density-dependent damage and mortality, thereby likely shaping plant community assembly, the response of belowground root feeders to changes in plant density has seldom been addressed. Locally rare plant species (with lower plant biomass per area) are often smaller with shallower roots than common species (with higher plant biomass per area) in competition-intensive grasslands. Likewise, root feeders are often distributed in the upper soil layers. We hypothesized therefore that root feeders would incur a negative density (biomass) dependent damage across plant species. To test this hypothesis, we investigated the diversity and abundance of plant and root feeder species in an alpine meadow, and determined the diet of the root feeders using metabarcoding. Across all species, root feeder load decreased with increasing aboveground plant biomass, root biomass, and total plant biomass per area, indicating negative density dependence of damage across plant species. Aboveground plant biomass per area increased with increasing individual plant biomass and root depth per area across species, suggesting that rare plant species were smaller in size and had shallower root systems compared to common plant species. Both root biomass per area and root feeder biomass per area decreased with soil depth, but the root feeder biomass decreased disproportionally faster compared to root biomass with increasing root depth. Root feeder load decreased with increasing root depth, but was not correlated with the feeding preference of root feeder species. Moreover, the prediction derived from a random process incorporating vertical distributions of root biomass and root feeder biomass significantly accounted for interspecific variation in root feeder load. In conclusion, the data indicate that root feeders incur negative density-dependent damage across plant species. On this basis, we suggest that manipulative experiments should be conducted to determine the effect of the negative density-dependent damage on plant community structure, and that different types of plant-animal interactions should be concurrently examined to fully understand the effect of plant density on overall herbivore damage across plant species.</p>
Do natural enemies mediate conspecific negative distance- and density-dependence of trees? A meta-analysis of exclusion experiments
<p>Conspecific negative distance- and density-dependence is believed to be one of the most important mechanisms controlling forest community assembly and species diversity globally. Plant pathogens, and insect and mammalian herbivores, are the most common natural enemy types that have been implicated in this phenomenon, but their general effects at different plant life stages are still unclear. Here, we conduct a meta-analysis of studies that involved robust manipulative experiments, using fungicides, insecticides, or exclosures, to assess the contributions of different natural enemy types to distance- and density-dependent effects at seed and seedling stages. We found that conspecific negative distance- and density-dependence was more common at the seedling stage. Only 30% of studies showed significant conspecific negative distance- and density-dependence. Among those studies, applying fungicides significantly reduced the effect of conspecific negative distance -dependent mortality. Excluding large mammals reduced the effect of conspecifics, but with only marginal significance (p < 0.1). Our study confirms that plant pathogens have a significant impact on distance -dependent mortality and suggests that the impacts of herbivores on seedlings have been understudied. At the seed stage, large and small mammals, respectively, appear to weaken and enhance negative conspecific distance-dependent mortality. Future research should identify specific agents of mortality, investigate the interactions among different enemy types, and assess how global change may affect natural enemies and thus influence the strength of conspecific distance- and density-dependence.</p>
Is negative density-dependent reproduction regulated by density-induced stress in root voles? Two field experiments
<p>Density dependence in reproduction plays an important role in stabilising population dynamics via immediate negative feedback from population density to reproductive output. Although previous studies have shown that negative density-dependent reproduction is associated with strong spacing behaviour and social interaction between individuals, the proximal mechanism for generating negative density-dependent reproduction remains unclear. In this study, we investigated the effects of density-induced stress on reproduction in root voles. Enclosed Founder populations were established by introducing six (low density) and 30 (high density) adults per sex into per enclosure (four enclosures per density in total) during the breeding season from April to July 2012 and from May to August 2015. Faecal corticosterone metabolite (FCM) levels, reproductive traits (recruitment rate and the proportion of reproductively active indivuduals), and founder population numbers were measured following repeated live-trapping in both years. The number of founders was negatively associated with recruitment rates and the proportion of reproductively active indivuduals, displaying a negative density-dependent reproduction. FCM level was positively associated with the number of founders. The number of founder females directly affected the proportion of reproductive females , and directly and indirectly through their FCM levels affected the recruitment rate; the effect of the number of male founders on the proportion of reproductive males was mediated by their FCM level. Our results showed that density-induced stress negatively affected reproductive traits and that density-induced stress is one ecological factor generating negative density-dependent reproduction.</p>
Data from: Positive spatial and temporal density-dependence drive early reproductive economy-of-scale effects of masting in a European old-growth forest community
<p>Masting, the spatial synchronization of interannual variation in seed production, can enhance reproductive efficiency through positive density-dependent processes (DD) that result in economies of scale (EOS), such as decreased pollen limitation and predator satiation in years of high reproduction. While the general occurrence of such EOS effects has been documented for masting species, few studies simultaneously investigated how spatial and temporal variation in reproduction affects pollination and predation. Furthermore, it is unclear whether the same mechanisms apply to co-occurring species with different levels of conspecific density, pollen limitation, and seed defenses. Here, we use a long-term data set with high spatial resolution of seed production of European beech (<em>Fagus sylvatica</em>), Norway spruce (<em>Picea abies</em>), and silver fir (<em>Abies alba</em>) in a primeval montane forest to investigate the relationship between reproductive effort, pollination efficiency, and predispersal predation by insects. We found that, along the temporal axis, the proportion of sound (fertilized and unpredated) seeds correlated positively with annual seed production over the 14-year study period in all three species, most strongly in beech and only weakly in silver fir. Moreover, the results show that in beech, spatial seed density interacts with plot-wide annual seed rain to enhance DD effects on seed predation, suggesting additive effects of synchronous reproduction on fitness benefits.</p> <p>Synthesis: For both pollination and predispersal predation in beech and spruce, the strongest DD effects occur at low levels of reproduction and quickly reach asymptotes at higher levels, suggesting the presence of thresholds in different EOS mechanisms. As variability and synchrony in mast-seeding are expected to decline with climate change, EOS effects driven by DD may remain stable until the threshold is reached, at which sudden declines would result in devastating effects on the availability of viable seeds for germination and recruitment.</p>
Data from: Density-dependent disease, life history tradeoffs, and the effect of leaf pathogens on a suite of co-occurring close relatives
1. Plant pathogens reduce the performance of their hosts and therefore may contribute to ecological mechanisms of coexistence. In Chesson's framework, pathogens contribute to stabilizing mechanisms when they intensify negative intraspecific interactions, such as density-dependent disease. Additionally, pathogens contribute to equalizing mechanisms when they reduce differences in performance among species. Life history tradeoffs predict higher susceptibility to pathogens in rapidly growing species, which could equalize performance among fast- and slow-growing species in the presence of pathogens. 2. In a coastal prairie in California, we studied the impact of leaf diseases on the performance of seventeen coexisting species of Trifolium and Medicago ("clovers"). We transplanted clovers in randomized arrays into the natural prairie community in three years of common garden experiments. We quantified infection rates by isolating fungi from leaves, and we measured disease severity as percent leaf area damaged. In a fungicide experiment, we measured the impact of infection on biomass and survival. We assessed whether disease on transplants was positively related to natural abundance of that species in the surrounding community, which we monitored over 5 years. We assessed life history tradeoffs by testing whether more rapidly growing species were more susceptible to pathogens. 3. Rank abundance of clover species was stable over five years despite marked environmental fluctuations. Across hosts, fungal infection was not linearly related to density, although transplants of species that were locally absent showed lower and more variable infection. Disease severity was greater for more abundant species in only one of three years, and response to fungicide was not stronger in more abundant species. Faster-growing species experienced greater fungal infection. Consistent with predictions of the leaf economic spectrum, the impact of infection on faster-growing species was less negative than for slower-growing species. 4. Our results suggest that life history tradeoffs in plant-pathogen interactions may contribute to equalizing mechanisms among species in this guild, but that the combined effects of greater infection with greater tolerance may limit rather than promote coexistence. We also found modest evidence that density-dependent disease may contribute to stabilizing mechanisms. Lack of host specificity, rapid evolution of host use, and temporal variation in climatic conditions may all influence the role that pathogens play in coexistence of these closely related plants.
Relatedness modulates density-dependent cannibalism rates in Drosophila
<p>1. Cannibalism is taxonomically widespread, and can have large impacts on individual fitness and population-level processes. As such, identifying how cannibalism rates vary in response to ecological cues is important for predicting species evolution and population dynamics.</p> <p>2. In this study, we aimed to identify several eco-evolutionary factors that affect cannibalism rate and measure how they interacted with one another.</p> <p>3. To do this, we conducted two experiments using complimentary methods to measure how cannibalism rates varied among larval Drosophila melanogaster and Drosophila simulans in response to changes in conspecific relatedness, social familiarity and density.</p> <p>4. We found that larvae were more likely to cannibalise non-related larval victims in both species, and that this effect increased at high densities in D. simulans. We found no evidence that Drosophila larvae use social familiarity to assess relatedness. Finally, in D. melanogaster, cannibalistic larvae prefer to cannibalise larvae that are being attacked by a greater number of conspecifics, implying that cues linked to conspecific abundance encourage cooperative cannibalism.</p> <p>5. By showing that cannibalism frequency in Drosophila spp. is sensitive to relatedness and several other factors, we reveal the complex relationship between cannibalism frequency and species ecology. Also, by showing that the effect of relatedness on cannibalism frequency is density-dependent, we advance the current understanding of how ecological variables interact to affect kin selection.</p> <p>ANALYSIS CODE IS WRITTEN IN R.</p>
Data from: Density-dependent reproductive success among sympatric dipterocarps during a major mast fruiting event
<p><span>The files hold the data for the paper entitled "</span>Density-dependent reproductive success among sympatric dipterocarps during a major mast fruiting event", which includes <span>(i) the weight and status of seeds collected with seed traps in a Bornean tropical forest during a mast fruiting event, and (ii) the results of a seed sowing experiment in primary and secondary forests. Study site was t</span>he Deramakot and Tangkulap Forest Reserves, Sabah, Malaysia (5°14– 30'N, 117°11–36'E)<span>.</span></p>
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>
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>
Is negative density-dependent reproduction regulated by density-induced stress in root voles? Two field experiments
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Insect root feeders incur negative density-dependent damage across plant species in an alpine meadow
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Do natural enemies mediate conspecific negative distance- and density-dependence of trees? A meta-analysis of exclusion experiments
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Allen Brain Atlas
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Annotated Behaviour and Observability Dataset (ABODe)
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The International Brain Laboratory public data releases expose standardized mouse decision-making experiments, including Neuropixels recordings, widefield calcium imaging, behavior, and session metadata accessed through the ONE API.
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