Forest fragmentation and defaunation drive an unusual ecological cascade: Predation release, monkey population outburst and plant demographic collapse

Portela, Rita de Cássia Quitete; Dirzo, Rodolfo

doi:10.1016/j.biocon.2020.108852

Cited by 21 publications

(18 citation statements)

References 62 publications

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“…Although nonsignificant ( p = 0.059), common palm civets' relative abundance and oil palm had a positive relationship at the local scale, suggesting the possibility of such a mechanism. We also propose that release from predation or competition are other potential explanations, since forest‐specialist predators and competitors decline in disturbed forests (De CQ Portela & Dirzo, 2020; Trewby et al, 2008). However, this study does not specifically test these hypotheses.…”

Section: Discussionmentioning

confidence: 96%

Common palm civets Paradoxurus hermaphroditus are positively associated with humans and forest degradation with implications for seed dispersal and zoonotic diseases

Dehaudt

Amir

Decoeur

et al. 2022

Journal of Animal Ecology

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Habitat loss and degradation can undermine wildlife communities and ecosystem functioning. However, certain generalist wildlife species like mesopredators and omnivores can exploit these disturbed habitats, sometimes leading to population increases (e.g. ‘mesopredator release’ in degraded areas). Although mesopredator release may cause negative effects on food webs and zoonotic disease management, some disturbance‐tolerant species may help perpetuate important ecological interactions, such as seed dispersal. We evaluated the habitat associations of common palm civets Paradoxurus hermaphroditus, which are widespread generalist mesopredators in Southeast Asia. Common palm civets are also high‐quality seed dispersers, and potential zoonotic disease hosts. We used published and new camera trapping data to map their probability of presence across Southeast Asia and evaluate regional‐scale associations between capture rates and habitat variables such as elevation, ecoregion intactness and Human Footprint Index, among others. We also assessed the influence of habitat variables on their relative abundance at the local scale. At the regional scale, we found that common palm civets showed significant positive associations with landscapes characterized by lower ecoregion intactness, higher Human Footprint Index and lower elevations. At the local scale, their relative abundance showed a significant positive association with higher Human Footprint Index, but only to a certain point, after which it started decreasing. They also favoured lower elevations at the local scale. These multi‐scale results indicate that common palm civets' abundance can increase under certain levels of human disturbances, consistent with the ‘mesopredator release’ hypothesis. This suggests they may be crucial seed dispersers in degraded forest landscapes, especially where more sensitive seed dispersers have disappeared. Our results are also consistent with previous studies reporting that habitat degradation increases populations of potential zoonotic disease hosts, and thus risks of transmission to humans.

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Section: Discussionmentioning

confidence: 96%

Common palm civets Paradoxurus hermaphroditus are positively associated with humans and forest degradation with implications for seed dispersal and zoonotic diseases

Dehaudt

Amir

Decoeur

et al. 2022

Journal of Animal Ecology

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“…Yet, by an excessive focus on the dichotomy of lianas versus trees, the limited number of studies available neglect the potentially important effects of defaunation on other dominant tropical growth forms, such as palms, and others at the understories including shrubs, herbs and bamboos. Evidence suggests that the spatial distribution and demography of palms, for example, might be affected by defaunation (Fragoso et al, 2003; Galetti et al, 2006; Portela & Dirzo, 2020; Valverde et al, 2020), but less is known about other ‘lesser’ growth forms.…”

Section: Introductionmentioning

confidence: 99%

Large mammalian herbivores modulate plant growth form diversity in a tropical rainforest

et al. 2022

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The world’s terrestrial biomes are broadly classified according to the dominant plant growth forms that define ecosystem structure and processes. Although the abundance and distribution of different plant growth forms can be strongly determined by factors such as climate and soil composition, large mammalian herbivores have a strong impact on plant communities, thus defaunation (the local or functional extinction of large animals) has the potential to alter the compositional structure of plant growth forms in natural ecosystems. Tropical rainforests sustain a high diversity of growth forms, including trees, palms, lianas, shrubs, herbs and bamboos, all of which play important ecosystem functions. Here, we experimentally evaluate how large mammalian herbivores affect the dominance, diversity and coexistence of these major tropical forest plant growth forms, by monitoring communities of saplings on the understorey in 43 paired exclusion plots in a long‐term replicated exclusion experiment in the understorey of the Atlantic forest of Brazil. Over the course of 10 years large herbivore exclusion decreased diversity among growth forms, increased the absolute abundance of palms and trees (22% and 38% respectively) and increased the diversity of species within these two groups, to the detriment of other growth forms. Furthermore, all pairwise relationships between growth forms were positive on plots where herbivores had access, whereas several strong negative relationships emerged in plots where herbivores were excluded. This occurred despite strong background directional temporal trends affecting plant communities in both experimental treatments across the region. Synthesis. Our work indicates that the defaunation alters growth form dominance by favouring palms and trees while eroding diversity among growth forms and coexistence on a temporal scale. Large herbivore mammals promote diversity among growth forms, preventing the hyper‐dominance of trees and palms, yet without supressing the diversity of species within growth forms. We argue that large herbivore mammals affect growth forms through several non‐mutually exclusive mechanisms, including herbivory, seed dispersal and physical disturbance, as well as differential effects linked to the morphological and physiological adaptations of growth forms. We conclude that defaunation might lead to profound impacts on important ecosystem functions underpinned by growth form diversity, and result in vertical and horizontal structural simplification of tropical rainforests.

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“…This was caused by heart-of-palm consumption by a hyper-abundant monkey population (Sapajus nigritus) in these areas. This dramatic population decline was detected in a 10-year plant demographic study in the same area (Portela and Dirzo, 2020). Apart from this disruptive interaction, this palm species seem to have higher capacity to overcome the challenges of high light availability or fluctuating light conditions (Schumann et al, 2017;Li et al, 2019), such as would occur in smaller fragments with more open canopy, sunflecks, or tree-fall gaps.…”

Section: Discussionmentioning

confidence: 88%

Linking Plant Functional Traits to Demography in a Fragmented Landscape

Portela

Colmenares-Trejos

Mattos

2021

Front. For. Glob. Change

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Habitat loss in highly deforested landscapes such as the Brazilian Atlantic Forest has been severely affecting the diversity and survival of palm species. As some species are more sensitive than others, trait responses to the environment, as well as environmental effects on fecundity, growth, and mortality rates, may affect species demography. Considering this context, we studied functional and demographic responses of three palm species (Astrocaryum aculeatissimum, Euterpe edulis, and Geonoma schottiana) to habitat loss in the Atlantic Forest in southeastern Brazil by measuring morpho-physiological traits related to plant growth and light acquisition for photosynthesis. We also tested the response of population fitness to fragment size. Plant survival and growth was subsequently monitored in 2006 and 2007, and population dynamics were summarized in pool matrices for large and small forest fragments in the monitoring periods comprehending one full year between 2005–2006 and 2006–2007. The asymptotic growth rate of populations (defined here as population fitness, λ) in five forest fragments was then calculated. Diameter of individuals of the demography plots (from year 2005 to 2007) was used to calculate the relative diameter growth rate. Later, in 2015, we measured a set of morpho-physiological functional traits in palms in the same plots used in the demographic studies. While A. aculeatissimum populations were stable in both monitoring periods in small and large fragments, E. edulis populations were predicted to decline due to intense predation by monkeys in the large fragment, but were stable in the smaller fragments, and G. schottiana populations were stable in the large fragments in both monitoring periods, but populations in the smaller fragments were predicted to decline in the second period, i.e., with lower fitness in these fragments. In addition, the functional traits analyzed showed that G. schottiana is a forest interior species associated with the shade/understory environment response. E. edulis was also affected by the size of the fragment, but due to a disruptive interaction with a predator and showed intermediate functional traits values. On the other hand, A. aculeatissimum thrived in areas with higher and lower incidence of light and was not demographically affected by forest remnant size. This suggests that E. edulis and A. aculeatissimum are habitat generalists. We concluded that differences in the ecophysiological performance of palms due to distinct morpho-physiological functional traits related to leaf economic spectrum, such as LDMC or specific leaf area (SLA) and to photosynthetic responses to light environment as electron transport rate (ETR) and saturation irradiance (Ik) were linked to the demographic variation observed in forest remnants of different size.

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Forest fragmentation and defaunation drive an unusual ecological cascade: Predation release, monkey population outburst and plant demographic collapse

Cited by 21 publications

References 62 publications

Common palm civets Paradoxurus hermaphroditus are positively associated with humans and forest degradation with implications for seed dispersal and zoonotic diseases

Common palm civets Paradoxurus hermaphroditus are positively associated with humans and forest degradation with implications for seed dispersal and zoonotic diseases

Large mammalian herbivores modulate plant growth form diversity in a tropical rainforest

Linking Plant Functional Traits to Demography in a Fragmented Landscape

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