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171 results for “density-dependent”

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Data from: Density-dependent dispersal strategy of pollinator moderates the adverse effect of habitat loss on plant reproduction

1. Major challenges for plant conservation are predicting the effect of habitat loss on pollination success and plant reproduction potential. 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. 2. To clarify the effect of pollinator movement on plant reproduction relative to habitat loss, we developed an integrated model incorporating pollinator's foraging response with its dispersal process mediated by a density-dependent dispersal (DDD) strategy. This model 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 (Tamarix chinensis) 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 (NHP) to explore the effect of habitat loss on plant reproduction. 3. Results suggested that saltcedar populations differ in their responses to habitat loss, which depended on the spatial scales considered. At landscape scale, increasing NHP significantly inhibited the dispersion extent of floral volatiles and therefore reduced pollinator visitation and subsequent seed production, especially when NHP exceeded the critical threshold of 0.6. 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. Plant reproduction was improved correspondingly in low-density and distant patches under different NHPs. 4. 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.

opencc-zeroDec 2022View details →

dryad32/100

Density-dependent patterns of multivariate selection on sperm motility and morphology in a broadcast spawning mussel

Sperm cells exhibit extraordinary phenotypic variation, both among taxa and within individual species, yet our understanding of the adaptive value of sperm trait variation across multiple contexts is incomplete. For species without the opportunity to choose mating partners, such as sessile broadcast spawning invertebrates, fertilisation depends on gamete interactions, which in turn can be strongly influenced by local environmental conditions that alter the concentration of sperm and eggs. However, the way in which such environmental factors impact phenotypic selection on functional gamete traits remains unclear in most systems. Here, we analyse patterns of linear and nonlinear multivariate selection under experimentally altered local sperm densities (densities within the capture zone of eggs) on a range of functionally important sperm traits in the broadcast spawning marine mussel, Mytilus galloprovincialis. Specifically, we assay components of sperm motility and morphology across two fertilisation environments that simulate either sperm limitation (when there are too few sperm to fertilise all available eggs), or sperm saturation (when there are many more sperm than required for fertilisation, and the risk of polyspermy and embryonic failure is heightened). Our findings reveal that the strength, form, and targets of selection on sperm depend on the prevailing fertilisation environment. In particular, our analyses revealed multiple significant axes of nonlinear selection on sperm motility traits under sperm limitation, but only significant negative directional selection on flagellum length under sperm saturation. These findings highlight the importance of local sperm densities in driving the adaptation of sperm phenotypes, particularly those related to sperm motility, in broadcast spawning invertebrates.

opencc-zeroJan 2023View details →

dryad32/100

Density-dependent changes in elk resource selection over successional time scales following forest disturbance

There is an increasing need to understand how animals respond to modifications of their habitat following landscape-scale disturbances such as wildfire or timber harvest. Such disturbances can promote increased use by herbivores due to changes in plant community structure that improve forage conditions, but can also cause avoidance if other habitat functions provided by cover are substantially reduced or eliminated. Quantifying the total effects of these disturbances, however, is challenging because they may not fully be apparent unless observed at successional timescales. Further, the effects of disturbances that improve habitat quality may be density dependent such that the benefits are 1) less valuable to high-density populations because the per-capita benefits are reduced when shared among more users, or alternatively, 2) more valuable to animals living in high densities because resources may be more depleted from greater intraspecific competition. We used 30 years of telemetry data on elk occurring at two distinct population densities to quantify changes in space use at diel, monthly, and successional timescales following timber harvest. Elk selected for logged areas at night only, with selection strongest during mid-summer, and peak selection occurring 14 years post-harvest but persisting for 26–33 years. This pattern of increased selection at night following a reduction in overhead canopy cover is consistent with elk exploiting improved nutritional conditions for foraging. The magnitude of selection for logged areas was 73% higher for elk at low population density, consistent with predictions from the ideal free distribution. Yet elk avoided these same areas during daytime up to 28 years post-logging and instead selected for untreated forest, suggesting a role for cover to meet other life history requirements. Our results demonstrate that while landscape-scale disturbances can lead to increased selection by large herbivores suggesting the improvement in foraging conditions can persist over short-term successional timescales, the magnitude of the benefits may not be equal across population densities. Further, the enduring avoidance of logging treatments during daytime indicates a need for structurally-intact forest and suggests that a mosaic of forest patches of varying successional stages and structural completeness will likely be most beneficial to large herbivores.

opencc-zeroMay 2023View details →

dryad32/100