Limited contributions of plant pathogens to density‐dependent seedling mortality of mast fruiting Bornean trees

Cannon, Patrick G.; O’Brien, Michael J.; Yusah, Kalsum M.; Edwards, David P.; Freckleton, Robert P.

doi:10.1002/ece3.6906

Cited by 9 publications

(8 citation statements)

References 67 publications

(158 reference statements)

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“…We found the insects had stronger effects on seed survival than fungi in defaunation treatments. This is consistent with results from a recent greenhouse experiment that found very weak effects of fungal pathogens on dipterocarp seedling mortality overall 53 . In fact, that study included three of the dipterocarp species we used, and their fungicide results were non-significant for Dryobalanops lanceolata and Parashorea malaanonan and significant for Shorea leprosula , which is exactly the pattern we observed in our field experiment.…”

Section: Discussionsupporting

confidence: 92%

Fungi and insects compensate for lost vertebrate seed predation in an experimentally defaunated tropical forest

2021

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Overhunting reduces important plant-animal interactions such as vertebrate seed dispersal and seed predation, thereby altering plant regeneration and even above-ground biomass. It remains unclear, however, if non-hunted species can compensate for lost vertebrates in defaunated ecosystems. We use a nested exclusion experiment to isolate the effects of different seed enemies in a Bornean rainforest. In four of five tree species, vertebrates kill many seeds (13–66%). Nonetheless, when large mammals are excluded, seed mortality from insects and fungi fully compensates for the lost vertebrate predation, such that defaunation has no effect on seedling establishment. The switch from seed predation by generalist vertebrates to specialist insects and fungi in defaunated systems may alter Janzen–Connell effects and density-dependence in plants. Previous work using simulation models to explore how lost seed dispersal will affect tree species composition and carbon storage may require reevaluation in the context of functional redundancy within complex species interactions networks.

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Section: Discussionsupporting

confidence: 92%

Fungi and insects compensate for lost vertebrate seed predation in an experimentally defaunated tropical forest

2021

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“…aromatica —up to 69 individuals per m 2 compared to <15 individuals per m 2 for Aiba and Nakashizuka (2007). This is comparable to reported field densities of 1–183 seeds per m 2 for mast fruiting dipterocarps (Canon et al, 2020). Thus, the high seedling density we used potentially increased our likelihood of detecting negative relationships between density and performance that would be present during masting fruiting episodes that characterize recruitment in this forest.…”

Section: Discussionsupporting

confidence: 89%

Interactions with soil fungi alter density dependence and neighborhood effects in a locally abundant dipterocarp species

Segnitz

Russo

Peay

2022

Ecology and Evolution

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Seedling recruitment can be strongly affected by the composition of nearby plant species. At the neighborhood scale (on the order of tens of meters), adult conspecifics can modify soil chemistry and the presence of host microbes (pathogens and mutualists) across their combined canopy area or rooting zones. At local or small spatial scales (on the order of one to few meters), conspecific seed or seedling density can influence the strength of intraspecific light and resource competition and also modify the density‐dependent spread of natural enemies such as pathogens or invertebrate predators. Intrinsic correlation between proximity to adult conspecifics (i.e., recruitment neighborhood) and local seedling density, arising from dispersal, makes it difficult to separate the independent and interactive factors that contribute to recruitment success. Here, we present a field experiment in which we manipulated both the recruitment neighborhood and seedling density to explore how they interact to influence the growth and survival of Dryobalanops aromatica, a dominant ectomycorrhizal tree species in a Bornean tropical rainforest. First, we found that both local seedling density and recruitment neighborhood had effects on performance of D. aromatica seedlings, though the nature of these impacts varied between growth and survival. Second, we did not find strong evidence that the effect of density on seedling survival is dependent on the presence of conspecific adult trees. However, accumulation of mutualistic fungi beneath conspecifics adults does facilitate establishment of D. aromatica seedlings. In total, our results suggest that recruitment near adult conspecifics was not associated with a performance cost and may have weakly benefitted recruiting seedlings. Positive effects of conspecifics may be a factor facilitating the regional hyperabundance of this species. Synthesis: Our results provide support for the idea that dominant species in diverse forests may escape the localized recruitment suppression that limits abundance in rarer species.

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“…However, there is increasing evidence that dipterocarps are weakly affected by conspecific density (Song et al., 2021), which may in part be due to their formation of ectomycorrhizal mutualisms (Segnitz et al., 2020). Ectomycorrhizal fungi often mediate positive plant–soil feedbacks (Bennet et al., 2017; Segnitz et al., 2020), nutrient exchange via common mycorrhizal networks (Liang et al., 2020) and defence from soil pathogens (Cannon et al., 2020) all of which would favour positive density dependence and promote local monodominance (Liang et al., 2020). Therefore, the largely neutral to positive density dependence shown here are likely due, in part, to these tree species forming ectomycorrhizal associations.…”

Section: Discussionmentioning

confidence: 99%

Topography in tropical forests enhances growth and survival differences within and among species via water availability and biotic interactions

O’Brien

Escudero

2021

Functional Ecology

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1. Topography is associated with variation in soil water, biogeochemical properties and climate, which drive diversity by filtering species and promoting niche differences. However, the potential for topography to promote fitness differences and diversity among tree species and populations remains poorly tested in tropical rainforests, especially at small spatial scales in everwet climates.2. We reciprocally transplanted tree seedlings between ridge and riparian sites and manipulated neighbour abundance and water availability to assess growth and survival differences both among species and between populations within species in response to changes in biotic interactions and soil water gradients associated with topographic heterogeneity.3. Seedling growth rates were higher on the ridge, but probability of survival was lower on the ridge than the riparian site. Topography also altered growth and survival responses to water availability such that seedlings in the inundated soils in the riparian site had the lowest growth and survival but increased rapidly with moderate soil drying. By contrast, growth and survival on the ridge were generally unresponsive to drying, although severe drought on the ridge reinforced differences among species in growth rates and probability of survival.4. The patterns of growth and survival within species did not provide evidence of local adaptation between seedlings from lowland and upslope origins. However, within species, topographic seed-origin determined the response of seedling growth and survival to increasing neighbour abundance, indicative of divergent selective pressures between individuals growing in different topographic environments. 5. Combined, these results suggest that topographic heterogeneity promotes tropical forest diversity both at the species level via environmental filtering due to water availability and at the population level via functional responses to the density of neighbouring vegetation.

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Limited contributions of plant pathogens to density‐dependent seedling mortality of mast fruiting Bornean trees

Cited by 9 publications

References 67 publications

Fungi and insects compensate for lost vertebrate seed predation in an experimentally defaunated tropical forest

Fungi and insects compensate for lost vertebrate seed predation in an experimentally defaunated tropical forest

Interactions with soil fungi alter density dependence and neighborhood effects in a locally abundant dipterocarp species

Topography in tropical forests enhances growth and survival differences within and among species via water availability and biotic interactions

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