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141 results for “species density”

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dryad36/100

Data for: Distance and density dependence in two native Bornean dipterocarp species

The Janzen-Connell hypothesis proposes that density and distance-dependent mortality generated by specialist natural enemies prevent competitive dominance. Much literature on Janzen Connell mechanisms comes from the neotropics, and evidence of the role of distance and density-dependence is still relatively sparse. We tested the predictions of the J-C hypothesis in a South-East Asian system dominated by mast fruiting species. We hypothesized that seedling survival would decrease with distance and density, seedling growth would increase, and herbivory would decrease, according to the predictions of the Janzen-Connell hypothesis. Experiments were conducted to determine the strength of the Janzen Connell mechanism by manipulating the density and identity of tree species as a function of the distance from parent trees. Survival of conspecific seedlings was reduced near adult trees of one species, but not another. High densities of seedlings decreased the growth of conspecific seedlings of both species. In both species, herbivory rates decreased with distance in low-density areas. This study indicates that dipterocarp species experienced weak Janzen-Connell effects of distance and density dependence at the growth stage studied. Future studies in this system might focus on earlier life-history stages such as seeds and small seedlings, as well as studying mortality during mast-seeding events.

opencc-zeroApr 2023View details →

dryad36/100

Effects of density on the strength of sexual selection in the lab and in nature in an undescribed amphipod species

There is a growing effort to understand how sexual selection varies over space and time under different ecological conditions and how this can maintain variation in sexual traits. An interesting ecological condition is population density, which can either increase or decrease sexual selection depending on the natural history of the species. We examined sexual and natural selection in an undescribed amphipod species (Hyalella sp.) using surveys of two natural populations that increase in density from spring to summer. We also conducted an experiment that directly manipulated density to assess the effects on sexual selection. In the field during spring (low density) and summer (high density), we documented sexual selection on male traits, including body size, gnathopods, and antennae. We discovered the magnitude and direction of this selection changed from spring to summer and selection patterns differed between populations. In the experiment, we found no sexual selection occurred at low density, but significant positive selection on all three male traits at medium and high densities. These results underscore the importance of isolating individual ecological factors to determine their role in sexual selection while also documenting patterns in natural populations to understand how selection varies over space and time.

opencc-zeroMay 2023View details →

dryad36/100

Effects of tree species diversity and conspecific seedling density on insect herbivory and pathogen infection on big-leaf mahogany seedlings

The Janzen-Connell Hypothesis (JCH) predicts that attack by specialist enemies on seedlings increases with conspecific seedling density, but studies have rarely experimentally tested for the contingency of such effects on tree community context (e.g., diversity, composition) and measured responses by different enemies (e.g. herbivores, pathogens). We conducted a field study in a large-scale system evaluating tree species diversity and conspecific density effects on leaf damage on mahogany (Swietenia macrophylla) seedlings. We established quadrats of eight levels of seedling density across mahogany tree monocultures and species polycultures including mahogany, and recorded percent leaf damage by insects and percent leaf necrosis by a pathogenic fungus on mahogany seedlings. We found contrasting effects of tree species diversity on insects and pathogens. Whereas diversity did not affect leaf damage by insects, it had a significant negative effect on leaf necrosis by pathogens. On average, percent leaf necrosis on mahogany seedlings in polyculture was half of that observed in monoculture. We discuss the potential influences of changes in mahogany tree density vs. frequency (relative to other tree species) driving this diversity effect. Unexpectedly, we found no effect of seedling conspecific density on either leaf insect or pathogen damage (i.e., density-independent attack). Likewise, we found no significant tree diversity by seedling density interaction, indicating that attackers were consistently unresponsive to variation in seedling density across two levels of tree diversity. Overall, this study provides a unique test of the JCH by experimentally evaluating seedling density and tree diversity effects on contrasting plant enemies, shedding light on enemy controls over plant recruitment.

opencc-zeroJun 2023View details →

zenodo36/100

Data for "Negative density dependence promotes persistence of a globally rare yet locally abundant plant species (Oenoethera coloradensis)"

This dataset was used to perform the analyses in the manuscript "Negative density dependence promotes persistence of a globally rare yet locally abundant plant species (Oenoethera coloradensis)"

opencc-by-4.0Oct 2023View details →

dryad36/100