scholarly journals Lack of negative density-dependence regulation in a dominant oak tree from a neotropical highland forest

2018 ◽  
Author(s):  
Irene Calderón-Sanou ◽  
Luis Diego Ríos ◽  
Alfredo Cascante-Marín ◽  
Gilbert Barrantes ◽  
Eric J. Fuchs
Keyword(s):  
Costa Rica ◽  
Density Dependence ◽  
Species Coexistence ◽  
Local Density ◽  
Seedling Survival ◽  
Forest Composition ◽  
Adult Density ◽  
Conspecific Density ◽  
Negative Density Dependence ◽  
Highland Forests

AbstractConspecific negative density-dependence(CNDD) is one of the main mechanisms proposed to regulate species coexistence. Tropical highland forests, in contrast to diverse lowland forests, are commonly dominated by a few tree species. Testing the importance of density-dependence effects on seedling establishment of dominant trees may provide insights on the mechanisms regulating population dynamics and forest composition of tropical highlands. We tested the importance of CNDD regulation on seedling survival and recruitment ofQuercus costaricensis, a monodominant oak in the Talamanca highland forests of Costa Rica. We used spatial statistics and generalized linear mixed models to test the effects of conspecific density, distance to the nearest adult, density ofChusqueabamboo shoots, and herbivory on the annual survival probability of 3538 seedlings between 2014 and 2017. We did not find any effect of CNDD on seedling survival. However, bamboo density and herbivory both significantly decreased seedling survival. All seedlings had signs of herbivory and predator satiation may explain the lack of density dependent regulation in this species. We argue that the lack of intraspecific density regulation at the seedling stage may explain the dominance ofQ. costaricensisin the highland forests of Costa Rica. Local density of this endemic oak is instead regulated by herbivory and the density ofChusquea.

scholarly journals Impacts of logging on density-dependent predation of dipterocarp seeds in a South East Asian rainforest

2011 ◽  
Vol 366 (1582) ◽  
pp. 3246-3255 ◽  
Author(s):  
Robert Bagchi ◽  
Christopher D. Philipson ◽  
Eleanor M. Slade ◽  
Andy Hector ◽  
Sam Phillips ◽  
...  
Keyword(s):  
East Asia ◽  
Large Scale ◽  
Species Coexistence ◽  
Seedling Survival ◽  
Spatial Scales ◽  
Small Scale ◽  
South East Asia ◽  
Similar Data ◽  
Neotropical Forests ◽  
Conspecific Density

Much of the forest remaining in South East Asia has been selectively logged. The processes promoting species coexistence may be the key to the recovery and maintenance of diversity in these forests. One such process is the Janzen–Connell mechanism, where specialized natural enemies such as seed predators maintain diversity by inhibiting regeneration near conspecifics. In Neotropical forests, anthropogenic disturbance can disrupt the Janzen–Connell mechanism, but similar data are unavailable for South East Asia. We investigated the effects of conspecific density (two spatial scales) and distance from fruiting trees on seed and seedling survival of the canopy tree Parashorea malaanonan in unlogged and logged forests in Sabah, Malaysia. The production of mature seeds was higher in unlogged forest, perhaps because high adult densities facilitate pollination or satiate pre-dispersal predators. In both forest types, post-dispersal survival was reduced by small-scale (1 m 2 ) conspecific density, but not by proximity to the nearest fruiting tree. Large-scale conspecific density (seeds per fruiting tree) reduced predation, probably by satiating predators. Higher seed production in unlogged forest, in combination with slightly higher survival, meant that recruitment was almost entirely limited to unlogged forest. Thus, while logging might not affect the Janzen–Connell mechanism at this site, it may influence the recruitment of particular species.

scholarly journals Immigration rates during population density reduction in a coral reef fish

2015 ◽  
Author(s):  
Katrine Turgeon ◽  
Donald L. Kramer
Keyword(s):  
Density Dependence ◽  
Local Density ◽  
Empirical Studies ◽  
Limited Area ◽  
Positive Density ◽  
Density Dependent ◽  
Novel Approach ◽  
Positive Density Dependence ◽  
Wide Range ◽  
Negative Density Dependence

AbstractAlthough the importance of density-dependent dispersal has been recognized in theory, few empirical studies have examined how immigration changes over a wide range of densities. In a replicated experiment using a novel approach allowing within-site comparison, we examined changes in immigration rate following the gradual removal of territorial damselfish from a limited area within a much larger patch of continuous habitat. In all sites, immigration occurred at intermediate densities but did not occur before the start of removals and only rarely as density approached zero. In the combined data and in 5 of 7 sites, the number of immigrants was a hump-shaped function of density. This is the first experimental evidence for hump-shaped, density-dependent immigration. This pattern may be more widespread than previously recognized because studies over more limited density ranges have identified positive density dependence at low densities and negative density dependence at high densities. Positive density dependence at low density can arise from limits to the number of potential immigrants and from behavioral preferences for settling near conspecifics. Negative density dependence at high density can arise from competition for resources, especially high quality territories. The potential for non-linear effects of local density on immigration needs to be recognized for robust predictions of conservation reserve function, harvest impacts, pest control, and the dynamics of fragmented populations.

scholarly journals Abiotic niche partitioning and negative density dependence drive tree seedling survival in a tropical forest

2017 ◽  
Vol 284 (1869) ◽  
pp. 20172210 ◽  
Author(s):  
Daniel J. Johnson ◽  
Richard Condit ◽  
Stephen P. Hubbell ◽  
Liza S. Comita
Keyword(s):  
Water Availability ◽  
Species Coexistence ◽  
Seedling Survival ◽  
Critical Role ◽  
Niche Partitioning ◽  
Time Factors ◽  
Plant Size ◽  
Forest Composition ◽  
Tree Seedling ◽  
Spatial And Temporal Patterns

In tropical tree communities, processes occurring during early life stages play a critical role in shaping forest composition and diversity through differences in species' performance. Predicting the future of tropical forests depends on a solid understanding of the drivers of seedling survival. At the same time, factors determining spatial and temporal patterns of seedling survival can play a large role in permitting species coexistence in diverse communities. Using long-term data on the survival of more than 45 000 seedlings of 238 species in a Neotropical forest, we assessed the relative importance of key abiotic and biotic neighbourhood variables thought to influence individual seedling survival and tested whether species vary significantly in their responses to these variables, consistent with niche differences. At the community level, seedling survival was significantly correlated with plant size, topographic habitat, neighbourhood densities of conspecific seedlings, conspecific and heterospecific trees and annual variation in water availability, in descending order of effect size. Additionally, we found significant variation among species in their sensitivity to light and water availability, as well as in their survival within different topographic habitats, indicating the potential for niche differentiation among species that could allow for species coexistence.

scholarly journals Positive density dependence acting on mortality can help maintain species-rich communities

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Thomas G Aubier
Keyword(s):  
Density Dependence ◽  
Species Coexistence ◽  
Equilibrium Points ◽  
Positive Density ◽  
Extrinsic Mortality ◽  
Positive Density Dependence ◽  
Negative Density Dependence ◽  
Competitive Species ◽  
Dependent Growth ◽  
Globally Stable

Conspecific negative density dependence is ubiquitous and has long been recognized as an important factor favoring the coexistence of competing species at local scale. By contrast, a positive density-dependent growth rate is thought to favor species exclusion by inhibiting the growth of less competitive species. Yet, such conspecific positive density dependence often reduces extrinsic mortality (e.g. reduced predation), which favors species exclusion in the first place. Here, using a combination of analytical derivations and numerical simulations, I show that this form of positive density dependence can favor the existence of equilibrium points characterized by species coexistence. Those equilibria are not globally stable, but allow the maintenance of species-rich communities in multispecies simulations. Therefore, conspecific positive density dependence does not necessarily favor species exclusion. On the contrary, some forms of conspecific positive density dependence may even help maintain species richness in natural communities. These results should stimulate further investigations into the precise mechanisms underlying density dependence.

Effects of forest fragmentation on the recruitment success of the tropical tree Poulsenia armata at Los Tuxtlas, Veracruz, Mexico

2014 ◽  
Vol 30 (3) ◽  
pp. 209-218 ◽  
Author(s):  
Jenny Zambrano ◽  
Rosamond Coates ◽  
Henry F. Howe
Keyword(s):  
Density Dependence ◽  
Seedling Survival ◽  
Abiotic Factors ◽  
Forest Fragments ◽  
Los Tuxtlas ◽  
Recruitment Success ◽  
Continuous Forest ◽  
Adult Trees ◽  
Negative Density Dependence ◽  
Survival And Growth

Abstract:Recruitment success of individual plants is limited by an array of biotic and abiotic factors. Seedling survival may experience high mortality due to negative density dependence or altered microclimatic conditions. This study reports regeneration of Poulsenia armata (Moraceae), in the fragmented landscape of the Los Tuxtlas region in south-eastern Mexico. Density, survival and growth of seedlings (<1 y) and juveniles (<150 cm height) of P. armata were predicted to be significantly lower in forest fragments compared with extensive continuous forest. Contrary to expectation, density did not vary between habitats; however, we found twice the number of seedlings (n = 82) in forest fragments than in the continuous forest (n = 35). Forest fragments were associated with higher seedling densities close to adult trees. Unexpectedly, we found no evidence for negative density dependence in plant survival or growth. Survival and growth of P. armata were negatively impacted in forest fragments, with desiccation by warmer daily temperatures likely the cause of mortality, independent of density. Of the 111 individuals recorded in 2010 in forest fragments, 38% died over 2 y of census (n = 42), while 9% (n = 12) of the 127 individuals from the continuous forest died. Higher rates of mortality suggest that conditions in forest fragments are detrimental to seedling cohorts over time. Low juvenile recruitment jeopardizes persistence of P. armata, in fragmented populations of this rain-forest tree.

scholarly journals Taxonomic scale-dependence of habitat niche partitioning and biotic neighbourhood on survival of tropical tree seedlings

2009 ◽  
Vol 276 (1676) ◽  
pp. 4197-4205 ◽  
Author(s):  
Simon A. Queenborough ◽  
David F. R. P. Burslem ◽  
Nancy C. Garwood ◽  
Renato Valencia
Keyword(s):  
Species Coexistence ◽  
Seedling Survival ◽  
Niche Partitioning ◽  
Local Variation ◽  
Tropical Tree ◽  
Tree Seedlings ◽  
Adult Density ◽  
Individual Survival ◽  
Tropical Tree Seedlings ◽  
Abiotic Habitat

In order to differentiate between mechanisms of species coexistence, we examined the relative importance of local biotic neighbourhood, abiotic habitat factors and species differences as factors influencing the survival of 2330 spatially mapped tropical tree seedlings of 15 species of Myristicaceae in two separate analyses in which individuals were identified first to species and then to genus. Using likelihood methods, we selected the most parsimonious candidate models as predictors of 3 year seedling survival in both sets of analyses. We found evidence for differential effects of abiotic niche and neighbourhood processes on individual survival between analyses at the genus and species levels. Niche partitioning (defined as an interaction of taxonomic identity and abiotic neighbourhood) was significant in analyses at the genus level, but did not differentiate among species in models of individual seedling survival. By contrast, conspecific and congeneric seedling and adult density were retained in the minimum adequate models of seedling survival at species and genus levels, respectively. We conclude that abiotic niche effects express differences in seedling survival among genera but not among species, and that, within genera, community and/or local variation in adult and seedling abundance drives variation in seedling survival. These data suggest that different mechanisms of coexistence among tropical tree taxa may function at different taxonomic or phylogenetic scales. This perspective helps to reconcile perceived differences of importance in the various non-mutually exclusive mechanisms of species coexistence in hyper-diverse tropical forests.

scholarly journals Conspecific negative density dependence and why its study should not be abandoned

Ecosphere ◽  
2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Joseph A. LaManna ◽  
Scott A. Mangan ◽  
Jonathan A. Myers
Keyword(s):  
Density Dependence ◽  
Negative Density Dependence
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