Pathogens, density dependence and the coexistence of tropical trees

Freckleton, Robert P.; Lewis, Owen T.

doi:10.1098/rspb.2006.3660

Cited by 152 publications

(163 citation statements)

References 60 publications

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“…Many studies of density dependence neglect to differentiate between effects of intra-and inter-specific densities, a key component in assessing the role of density dependence in promoting species coexistence (Freckleton and Lewis 2006). We found a clear difference between conspecific and heterospecific neighbor effects at the community level, and for approximately one-half of the focal species examined.…”

Section: Effect Of Heterospecific Neighbors On Survivalmentioning

confidence: 70%

“…A CCT would also fail to arise if species always experienced high local densities of conspecifics, regardless of their abundance in the community, due to limited seed dispersal (Freckleton and Lewis 2006). Additionally, predator satiation at larger spatial scales could result in a positive relationship between seedling survival and species abundance, even in the face of local-scale negative density dependence (Schupp 1992).…”

Section: Community-level Consequences Of Local Density Dependencementioning

confidence: 99%

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Local neighborhood and species' shade tolerance influence survival in a diverse seedling bank

Comita

Hubbell

2009

Ecology

214

248

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bstract. Accumulating evidence suggests that negative density dependence, particularly at early life stages, is widespread in plant communities. We hypothesized that survival in forest seedling banks declines with increasing density of conspecific neighbors and that localscale effects cause a negative correlation between seedling survival and tree species abundance in the community. We tested these hypotheses using data on 48 956 established seedlings of 235 species over three years in a 50-ha plot in Panama. For all species combined, we found a significant negative effect of conspecific seedling and adult neighbors within 10 m. In species-level analyses, neighbor density affected survival for 45 of 59 species, with effects of conspecifics different from heterospecifics for 29 species. Despite negative effects of local conspecific neighbors, seedling survival tended to be positively correlated with species abundance at the 50-ha scale. However, when accounting for species' shade tolerance, we found a significant negative relationship between seedling survival and species' basal area, but not density, in the 50-ha plot. Our findings indicate that attempts to quantify the contribution of density dependence to tropical tree species coexistence must integrate effects of neighbors across multiple life stages and should also take into account variation in life history strategy.

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Section: Effect Of Heterospecific Neighbors On Survivalmentioning

confidence: 70%

Section: Community-level Consequences Of Local Density Dependencementioning

confidence: 99%

Local neighborhood and species' shade tolerance influence survival in a diverse seedling bank

Comita

Hubbell

2009

Ecology

214

248

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“…Along with fungi and insects, the Oomycota have long been thought to be one of the drivers of the JanzenConnell model. However, the degree of host-specificity is unknown for most Oomycota species 46 , and a fungicide study in Belize documented a non-significant effect by these protists 6 . If the Oomycota broadly drive the Janzen-Connell model, then we can expect their diversity to be very high, mirroring tree diversity.…”

Section: Discussionmentioning

confidence: 99%

Parasites dominate hyperdiverse soil protist communities in Neotropical rainforests

et al. 2017

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High animal and plant richness in tropical rainforest communities has long intrigued naturalists. It is unknown if similar hyperdiversity patterns are reflected at the microbial scale with unicellular eukaryotes (protists). Here we show, using environmental metabarcoding of soil samples and a phylogeny-aware cleaning step, that protist communities in Neotropical rainforests are hyperdiverse and dominated by the parasitic Apicomplexa, which infect arthropods and other animals. These host-specific parasites potentially contribute to the high animal diversity in the forests by reducing population growth in a density-dependent manner. By contrast, too few operational taxonomic units (OTUs) of Oomycota were found to broadly drive high tropical tree diversity in a host-specific manner under the Janzen-Connell model. Extremely high OTU diversity and high heterogeneity between samples within the same forests suggest that protists, not arthropods, are the most diverse eukaryotes in tropical rainforests. Our data show that protists play a large role in tropical terrestrial ecosystems long viewed as being dominated by macroorganisms.S ince the works of early naturalists such as von Humboldt and Bonpland 1 , we have known that animal and plant communities in tropical rainforests are exceedingly species rich. For example, one hectare can contain more than 400 tree species 2 and one tree can harbour more than 40 ant species 3 . This hyperdiversity of trees has been partially explained by the Janzen-Connell model 4,5 , which hypothesizes that host-specific predators and parasites reduce plant population growth in a density-dependent manner 6,7 . Sampling up in the tree canopies and below on the ground has further led to the view that arthropods are the most diverse eukaryotes in tropical rainforests 8,9 .The focus on eukaryotic macroorganisms in these studies is primarily because they are familiar and readily observable to us. We do not know whether the less familiar and less readily observable protists-microbial eukaryotes that are not animals, plants or fungi 10 -inhabiting these same ecosystems exhibit similar diversity patterns. To evaluate if macroorganismic diversity patterns are reflected at the microbial scale with protists, we conducted an environmental DNA metabarcoding study by sampling soils in 279 locations in a variety of lowland Neotropical forest types in La Selva Biological Station, Costa Rica, Barro Colorado Island, Panama and Tiputini Biodiversity Station, Ecuador. This metabarcoding approach has the power to uncover known and new taxa on a massive scale 11 . By amplifying DNA extracted from the soils with broadly targeted primers for the V4 region of 18S rRNA and sequencing it using the Illumina MiSeq platform, we were able to detect most eukaryotic lineages, and assess the diversity and relative dominance of free-living and parasitic lineages.

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“…It is of particular interest whether disease spread and the effect of a pathogen on plant fitness are dependent on the density of the host population. If effects of pathogens increase with plant density, pathogens have the potential to regulate host population size and alter spatial distributions (4,51). Several studies have demonstrated important density-dependent effects of disease in natural plant populations (18,21,55,75).…”

Section: Population Ecology and Geneticsmentioning

confidence: 99%

“…First, there is a need to dissect the black box of the soil community to understand which organisms and combinations contribute to ecologically relevant effects (106). Second, more detailed studies of patterns of plant density dependence, host specificity of pathogens, and the entire plant life cycle are needed to fully explore these hypotheses (51).…”

Section: Community and Ecosystem Ecologymentioning

confidence: 99%

Disease in Natural Plant Populations, Communities, and Ecosystems: Insights into Ecological and Evolutionary Processes

Alexander

2010

Plant Disease

105

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Pathogens are associated with virtually all plant species, from a diverse array of habitats. Although we know the most about diseases of economically important plants, the goal of this article is to describe current work on host-pathogen interactions in natural or unmanaged systems outside of the crop field or forestry plantation. Agricultural scientists, of course, have contributed to this research. For example, disease resistance genes are often discovered as a result of surveys of wild relatives of crop plants, and it is well known that crop disease levels can be influenced by diseases in nearby weeds. Starting in the late 1970s, however, research on natural plant-pathogen interactions began to both increase and diversify, with an explicit goal of understanding the ecology and evolution of these interactions. This article will trace the history of this young discipline and provide highlights of ongoing research areas. I will focus on work by ecologists and evolutionary biologists that often is not published in plant pathology or forestry journals.A first step is to define a natural system as opposed to an agricultural or human-managed system. In contrast to most row crops, most natural populations occur in complex spatial arrangements with tens to hundreds of other species, are genetically diverse, and consist of plants of different ages and developmental stages. Seeds produced by a population in one year are the source of future generations at the site. Natural populations need not be pristine; as defined above, roadside weeds are as natural as prairie wildflowers. This natural versus agricultural dichotomy is also, of course, simplistic. Forest plantations and pasture landscapes have many natural attributes, and the degree of distinction between agricultural and natural ecosystems varies around the world.Although there have always been researchers intrigued by the role of pathogens in nature (58), publications in the 1970s and 1980s were influential in introducing the study of plant disease to ecologists and evolutionary biologists. For example, John Harper, a British biologist, published a landmark book in 1977 called Population Biology of Plants (61). This large tome (892 pages) encouraged ecologists to view plants not as vegetation, but as populations of individuals. One of his 17 chapters was titled "Pathogens" and emphasized the effect that disease could have on the structure and dynamics of plant populations and communities. Harper's book was followed a decade later by Jeremy Burdon's 1987 book Diseases and Plant Population Biology (30). Burdon expanded on the ecological consequences of disease and also emphasized genetic interactions between host and pathogen. Both Harper and Burdon emphasized the relevance of crop research and theories developed in an agricultural context, such as van der Plank's (101) work in epidemiology and Flor's gene-for-gene hypothesis (50). Interestingly, at the same time period, several plant pathologists were discussing disease in natural systems (130). Browning (29), in pa...

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Pathogens, density dependence and the coexistence of tropical trees

Cited by 152 publications

References 60 publications

Local neighborhood and species' shade tolerance influence survival in a diverse seedling bank

Local neighborhood and species' shade tolerance influence survival in a diverse seedling bank

Parasites dominate hyperdiverse soil protist communities in Neotropical rainforests

Disease in Natural Plant Populations, Communities, and Ecosystems: Insights into Ecological and Evolutionary Processes

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