Herbivores as drivers of negative density dependence in tropical forest saplings

Forrister, Dale L.; Endara, María‐José; Younkin, Gordon C.; Coley, Phyllis D.; Kursar, Thomas A.

doi:10.1126/science.aau9460

Cited by 101 publications

(121 citation statements)

References 60 publications

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“…refs. 57,58 ), on the basis of the evidence presented here, insects and plant-associated fungi appear to play a greater role in mediating conspecific density dependence than large herbivores.…”

Section: Discussionmentioning

confidence: 68%

Tree species traits affect which natural enemies drive the Janzen-Connell effect in a temperate forest

et al. 2020

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A prominent tree species coexistence mechanism suggests host-specific natural enemies inhibit seedling recruitment at high conspecific density (negative conspecific density dependence). Natural-enemy-mediated conspecific density dependence affects numerous tree populations, but its strength varies substantially among species. Understanding how conspecific density dependence varies with species' traits and influences the dynamics of whole communities remains a challenge. Using a three-year manipulative community-scale experiment in a temperate forest, we show that plant-associated fungi, and to a lesser extent insect herbivores, reduce seedling recruitment and survival at high adult conspecific density. Plant-associated fungi are primarily responsible for reducing seedling recruitment near conspecific adults in ectomycorrhizal and shade-tolerant species. Insects, in contrast, primarily inhibit seedling recruitment of shade-intolerant species near conspecific adults. Our results suggest that natural enemies drive conspecific density dependence in this temperate forest and that which natural enemies are responsible depends on the mycorrhizal association and shade tolerance of tree species.

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Section: Discussionmentioning

confidence: 68%

Tree species traits affect which natural enemies drive the Janzen-Connell effect in a temperate forest

et al. 2020

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“…A recent experimental study, which looked at monocultures vs. mixed seedlings exposed to drought, suggested that competition for water in drought environment was reduced in more diverse neighborhoods (O'Brien et al 2017). However, this probably cannot be used to explain the patterns we found as competition for limiting resources has been considered to be weak to nonexistent in diverse forests (Paine et al 2008, Forrister et al 2019. A third possibility is that the effects of the surrounding neighborhoods tell more about local habitat heterogeneity than biotic interactions (Comita and Hubbell 2009).…”

Section: Discussionmentioning

confidence: 91%

“…, Forrister et al. ). A third possibility is that the effects of the surrounding neighborhoods tell more about local habitat heterogeneity than biotic interactions (Comita and Hubbell ).…”

Section: Discussionmentioning

confidence: 99%

Neighborhood effects explain increasing asynchronous seedling survival in a subtropical forest

Chen

Wang

et al. 2019

Ecology

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Biotic interactions play a critical role in mediating community responses to temporal environmental variation, but the importance of these effects relative to the direct effects of environmental change remains poorly understood, particularly in diverse forest communities. Here we combine a neighborhood modeling approach with insights from coexistence theory to assess the effects of temporal variation in species interactions and environmental conditions (e.g., precipitation, temperature, and understory light availability) on seedling survival over nine census years in a subtropical forest. We find significant temporal shifts in the magnitude of neighborhood effects on both community‐wide and species‐level seedling survival (statistically significant random effects of neighborhood × year and neighborhood × species × year interactions). These results are consistent with the idea that environmental change will play a fundamental role on forest regeneration dynamics by altering biotic interactions at the neighborhood scale. Moreover, differences among species in response to neighbors over time contribute to a pattern of temporal decoupling of seedling survival between species, which can help to promote diversity in certain contexts. In separate analyses of multiple regression on distance matrices (MRM), altered interactions with neighbors are much stronger predictors of asynchronous seedling survival among species than the pure effects of climate and plant functional traits, explaining twice as much variation (43.9% vs. 22.2%). In sum, these results reveal that divergent species responses to interannual environmental variability detected are driven primarily by indirect effects mediated by changing biotic environments. This highlights the importance of including indirect effects from local biotic (neighborhood) interactions in forecasts of forest community responses to global change.

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“…It is possible though that the duration of our study was insufficient to pick up the effects of insects and fungal enemies on established seedlings, which may occur over longer time scales. For example, insect herbivores can alter survival and growth of older seedlings and saplings (Forrister et al, 2019), but these effects may take years to manifest, particularly in terms of aggregate community responses such as diversity or composition. Similarly, fungi infect established seedlings and saplings and impact their growth and survival (Gilbert and Webb, 2007), and foliar fungal infection and associated plant performance can be altered by fragmentation (Benitez-Malvido et al, 1999;Benítez-Malvido et al, 2018).…”

Section: Edge Effects On Insect and Fungal Regulation Of Seedling DIVmentioning

confidence: 99%

Edge Effects on Seedling Diversity Are Mediated by Impacts of Fungi and Insects on Seedling Recruitment but Not Survival

Krishnadas

Comita

2019

Front. For. Glob. Change

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Growing awareness of the role of enemies in plant community dynamics has led to ecologists exploring how plant-enemy interactions change in human-modified systems. Proximity to forest edges was found to weaken the role of two groups of plant enemies-insect herbivores and fungal pathogens-in increasing plant diversity during the seed-to-seedling transition. However, it is less clear whether edge effects similarly compromise the diversifying effects of fungi and insects on established seedlings. We examined this question in a human-modified wet tropical forest in the Western Ghats of southern India. Over an annual cycle of recruitment, in 730 seedling plots (1 × 1 m each) arrayed at distances 0-100 m from the forest edge across 15 locations in a 30 km 2 landscape, we suppressed the activity of fungal pathogens and insect herbivores by applying fungicide and insecticide to soil, seeds, and seedlings in a subset of plots. Suppressing fungi and insects reduced diversity mainly for seedling recruits and not for seedlings that had already established. However, pesticide effects were only apparent at 90-100 m from forest edges. Specifically, in the interior sites, fungi and insect activity increased recruit diversity, which helped maintain local seedling diversity even though diversity of established seedlings declined with annual mortality. By comparison, canopy openness affected neither the diversity of survivors from the initial seedling cohort nor total seedling diversity after an annual cycle of recruitment. Our results indicate that insects and fungi promote diversity more prominently during early seedling establishment rather than through impacts on post-establishment seedling survival. Thus, edge effects can weaken the diversifying effects of plant-insect and plant-fungal interactions during recruitment and thereby modify the seedling template available for the future tree community in human-modified forests.

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Herbivores as drivers of negative density dependence in tropical forest saplings

Cited by 101 publications

References 60 publications

Tree species traits affect which natural enemies drive the Janzen-Connell effect in a temperate forest

Tree species traits affect which natural enemies drive the Janzen-Connell effect in a temperate forest

Neighborhood effects explain increasing asynchronous seedling survival in a subtropical forest

Edge Effects on Seedling Diversity Are Mediated by Impacts of Fungi and Insects on Seedling Recruitment but Not Survival

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