1. In forest fragments, edge effects can influence forest regeneration, but little is known about how edge effects influence seedling performance and the interaction between seedlings and their ...natural enemies over time. 2. In central Amazonia, we recorded survival and growth (in height and leaf number)and damage by insect herbivores and leaf-fungal pathogens of Chrysophyllum pomiferum (Sapotaceae) seedlings that were exposed to different numbers of edges and to different distances from the forest edge. Grown seedlings were transplanted into one-square-metre plots within 1-ha blocks located in the centre (no edge), the edge (one edge), and the corner (two edges), and at different distances from the edge towards the interior (i.e., 20, 40, 60, 80, and 100 m) of two rectangular fragments (10- and 100-ha in size). Plots were visited once every 2 months for 1 year (1992-1993) and thereafter every 2 years for almost 8 years (1993-2001). 3. Overall, results showed that seedling survival, height, leaf number, and biotic damage varied over time with the presence of nearby edges and with the distance from the edge. Survival was lower in fragment edges and corners than in centres. Increase in height was similar for all positions within the 100-ha fragment, whereas in the 10-ha centre. Furthermore, survival increased with distance from the edge as did leaf number, whereas height showed a lower increase closer to the edge than farther away. 4. Regarding biotic damage, for both fragments herbivory was greater at the centres and decreased with edge proximity over time, whereas leaf-fungal damage was greater at the corners than in the edges and increased significantly over time. Biotic damage was correlated with seedling size. Small seedlings were more susceptible to fungal attack, whereas larger seedlings were so to herbivores. 5. Synthesis. This study demonstrated that despite stochastic environmental factors seedling survival, growth, and biotic damage by herbivores and fungal pathogens varied with the level of edge exposure and proximity, which may threaten forest regeneration in the long term.
We evaluated the importance of small (<5 ha) forest patches for the conservation of regional plant diversity in the tropical rainforest of Los Tuxtlas, Mexico. We analyzed the density of plant ...species (number of species per 0.1 ha) in 45 forest patches of different sizes (1-700 ha) in 3 landscapes with different deforestation levels (4, 11, and 24% forest cover). Most of the 364 species sampled (360 species, 99%) were native to the region, and only 4 (1%) were human-introduced species. Species density in the smallest patches was high and variable; the highest (84 species) and lowest (23 species) number of species were recorded in patches of up to 1.8 ha. Despite the small size of these patches, they contained diverse communities of native plants, including endangered and economically important species. The relationship between species density and area was significantly different among the landscapes, with a significant positive slope only in the landscape with the highest deforestation level. This indicates that species density in a patch of a given size may vary among landscapes that have different deforestation levels. Therefore, the conservation value of a patch depends on the total forest cover remaining in the landscape. Our findings revealed, however, that a great portion of regional plant diversity was located in very small forest patches (<5 ha), most of the species were restricted to only a few patches (41% of the species sampled were distributed in only 1-2 patches, and almost 70% were distributed in 5 patches) and each landscape conserved a unique plant assemblage. The conservation and restoration of small patches is therefore necessary to effectively preserve the plant diversity of this strongly deforested and unique Neotropical region.
We synthesize findings to date from the world’s largest and longest-running experimental study of habitat fragmentation, located in central Amazonia. Over the past 32
years, Amazonian forest ...fragments ranging from 1 to 100
ha have experienced a wide array of ecological changes. Edge effects have been a dominant driver of fragment dynamics, strongly affecting forest microclimate, tree mortality, carbon storage, fauna, and other aspects of fragment ecology. However, edge-effect intensity varies markedly in space and time, and is influenced by factors such as edge age, the number of nearby edges, and the adjoining matrix of modified vegetation surrounding fragments. In our study area, the matrix has changed markedly over the course of the study (evolving from large cattle pastures to mosaics of abandoned pasture and regrowth forest) and this in turn has strongly influenced fragment dynamics and faunal persistence. Rare weather events, especially windstorms and droughts, have further altered fragment ecology. In general, populations and communities of species in fragments are hyperdynamic relative to nearby intact forest. Some edge and fragment-isolation effects have declined with a partial recovery of secondary forests around fragments, but other changes, such as altered patterns of tree recruitment, are ongoing. Fragments are highly sensitive to external vicissitudes, and even small changes in local land-management practices may drive fragmented ecosystems in markedly different directions. The effects of fragmentation are likely to interact synergistically with other anthropogenic threats such as logging, hunting, and especially fire, creating an even greater peril for the Amazonian biota.
The maintenance of seedling diversity of animal-dispersed tree species is fundamental for the structure and function of forest patches in fragmented tropical rainforests. Nonetheless, the effects of ...landscape structure at different spatial scales on α- and β-diversity of tree seedling communities are recently explored. Using a multi-scale approach, we assessed the relative effect of landscape composition and configuration on α- and β-diversity of animal-dispersed seedlings within 16 forest patches in the Lacandona rainforest, Mexico. We assessed these effects at 13 spatial scales (from 300 to 1500 m radius, at 100 m intervals) for three metrics of effective number of species considering α- and β-diversity. We found that α-diversity was largely affected by landscape composition and β-diversity by landscape configuration. On the one hand, the amount of secondary forest influenced α-diversity. Additionally, species richness increased in landscapes with highly aggregated forest patches. On the other hand, β-diversity was affected positively by forest fragmentation and negatively by the edge contrast of forest patches with the surrounding matrix. Our findings indicate that landscape configuration is a strong driver of seedling diversity in highly deforested rainforests. Promoting forest patches and secondary forests through payment for ecosystem services' programs, favoring matrix quality within land-sharing schemes of smallholder agriculture and secondary forest management, and identifying restoration opportunities for assisted or unassisted natural regeneration are urgently needed for conservation of seedling diversity in human-modified tropical landscapes.
Premise
Primates are important seed dispersers, especially for large‐seeded (>1 cm long) tropical species in continuous and fragmented rainforests.
Methods
In three forest fragments within the Montes ...Azules Biosphere Reserve, southern Mexico, we investigated the effect of seed passage through the gut of howler monkeys (Alouatta pigra) on the germination rate and maximum germination (%) of native, large‐seeded species. One group of howler monkeys, per fragment, was followed and fresh feces collected. Large seeds were removed to compare their germination success with non‐ingested seeds of the same species collected underneath parent plants.
Results
Feces contained large seeds from seven tree species (Ampelocera hottlei, Castilla elastica, Dialium guianense, Garcinia intermedia, Pourouma bicolor, Spondias mombin, Trophis racemosa) and one liana species (Abuta panamensis). Except for G. intermedia, ingested seeds germinated significantly faster than non‐ingested seeds, which had negligible germination. Ingested seeds of D. guianense, P. bicolor, S. mombin, T. racemosa, and A. panamensis had significantly greater germination, while G. intermedia had significantly lower germination and seed ingestion had no apparent effect for A. hottlei and C. elastica.
Conclusions
In general, seed ingestion by howler monkeys confers faster germination compared with non‐ingested seeds. Faster germination reduces predation probabilities and increases seedling establishment in forest fragments. Primate dispersal services contribute to germination heterogeneity within plant populations of old‐growth forest species and to their persistence in forest fragments.
Flagship species are those chosen to raise support for broader conservation marketing campaigns and can be used as symbols of the ecosystem services and evolutionary history of particular areas. ...Thus, flagship species can be employed for the protection of endangered species and threatened ecosystems. Northeastern Michoacán, Mexico, is an important region for amphibian diversity but approximately 40% of its mature forest has been removed. Among northeastern Michoacán amphibians, the use of Ambystoma ordinarium as a flagship species is supported by its co-occurrence with other threatened amphibians along riparian zones. To support this proposal, however, it is important to assess the functional traits and evolutionary history of amphibian species sharing their habitat with A. ordinarium. To evaluate the potential of A. ordinarium as a flagship species, we estimated the functional and phylogenetic diversity of amphibian assemblages in 60 riparian zones. The results showed that amphibian assemblages sharing habitat with A. ordinarium presented higher functional and phylogenetic diversity than those in which this species was absent. These results highlight the potential of A. ordinarium as a flagship species for the protection of associated amphibian species, their functions, and evolutionary history.
• Premise of the study: Over the past two decades an interest in the role that plant-animal mutualistic networks play in the organization and dynamic of biodiversity has steadily risen. Despite the ...ecological, evolutionary, and economic importance of plant-herbivore and plant-pathogen antagonistic relationships, however, few studies have examined these interactions in an ecological network framework. • Methods: We describe for the first time the topological structure of multitrophic networks involving congeneric tropical plant species of the genus Heliconia (Heliconiaceae, Zingiberales) and their herbivores and pathogens in the state of Pernambuco, Brazil. We based our study on the available literature describing the organisms (e.g., insects, mites, fungi, and bacteria) that attack 24 different species, hybrids, and cultivated varieties of Heliconia. • Key results: In general, pathogen-and herbivore-Heliconia networks differed in their topological structure (more modular vs. more nested, respectively): pathogen-Heliconia networks were more specialized and compartmentalized than herbivore-Heliconia networks. High modularity was likely due to the high intimacy that pathogens have with their host plants as compared with the more generalized feeding modes and behavior of herbivores. Some clusters clearly reflected the clustering of closely related cultivated varieties of Heliconia sharing the same pathogens. • Conclusions: From a commercial standpoint, different varieties of the same Heliconia species may be more susceptible to being attacked by the same species of pathogens. In summary, our study highlights the importance of interaction intimacy in structuring trophic relationships between plants and pathogens in the tropics.
•Abundance of herpetofauna decreased more than 50% after hurricanes in old growth forest.•Species evenness of herpetofauna increased after hurricane Patricia.•Presence of secondary forests buffers ...the negative impact of hurricanes on herpetofauna.•Snake assemblages were on average 98% dissimilar between pre hurricanes and post hurricane Patricia.
If combined with anthropogenic disturbances and global climatic change, hurricanes may lead to major effects on animal populations and assemblages. The combined effects of cumulative natural and human disturbances on vertebrates have been little studied. There is evidence that herpetofaunal assemblages are sensitive in species richness, abundance, and diversity to anthropogenic and natural disturbances, or to their interaction. In the Pacific coast of Jalisco, Mexico, we aimed to evaluate the cumulative effects of hurricanes Jova (2011) and Patricia (2015) on herpetofaunal assemblages along tropical dry forest successional stages by comparing before and after the hurricanes. We conducted a long-term survey (2009 to 2018) on anuran, lizard and snake populations within five dry forest successional stages (from 0 to > 50 years after forest clearance), including the following: active pastures, early forests, young forests, intermediate forests, and old-growth forests as experimental controls. We hypothesized that cumulative effects of hurricanes will result in a general pattern of a decrease in abundance, richness and diversity, and an increase in evenness of anurans, lizards and snakes. We also expected that herpetofaunal diversity will decrease and evenness will increase in those stages with higher vegetation complexity, such as old-growth forest (OGF), and an increase in similarity and evenness in herpetofaunal assemblages in all successional stages. Overall, the abundance of anurans, lizards and snakes significantly decreased after hurricanes, but only for lizards and anurans the interaction of successional stage-hurricane was significant. Furthermore, species richness and diversity increased for lizards and decreased for snakes after hurricanes landed. Although, the pattern of anuran species richness among successional stages was similar after hurricanes, the richness in OGF markedly diminished after hurricanes.
Interestingly our results showed that tropical dry secondary forests, under the impact of low intensity hurricanes, might function as buffers that promote herpetofauna resilience. However, cumulative effects of hurricanes resulted in a homogenization tendency among successional stages, suggesting a negative effect for ecosystem functioning. The changes in the buffering role of secondary forests highlights the importance of these ecosystems for conserving biodiversity in times when hurricane disturbances are increasing in frequency and intensity. Overall, we discuss how the complex interactions between human and natural disturbances such as hurricanes might be a factor that contributes to maintain biotic diversity in anthropic landscapes of tropical dry forests.
Questions
The ecological condition of riparian habitats has been negatively altered by human activities and land‐use changes. The aims of this study were to evaluate: (a) how adjacent land use ...affects the ecological condition of riparian habitats; and (b) whether the ecological condition relates to riparian vegetation properties (i.e., structure, diversity, and species composition).
Location
Watershed of the Duero River, in the state of Michoacán, Mexico.
Methods
Sampling sites were established along the Duero River riverbank by considering three different land uses (i.e., native forest, agriculture, and urban). At each site, we assessed the ecological condition of riparian habitats with a riparian condition index (RCI) composed of six subindices, with 17 indicators. Using a survey of woody plants (DBH ≥ 2.5 cm) in 12 different 0.1‐ha sites, we assessed vegetation properties.
Results
According to the RCI, 76% of the studied riparian habitats had a very poor ecological condition, and only one site scored an excellent condition. The values of all subindices as well as the RCI were significantly greater in the forest than in the agricultural or urban land uses. The significant relationships between the RCI and its components (subindices) with vegetation properties were all positive and explained between 22% and 73% of the variation in structural and diversity attributes, and between 48% and 66% in floristic composition.
Conclusions
This study shows how human land‐use activities affect the ecological condition of riparian habitats and hence riparian forests. Overall, the RCI had a high predictive power for the vegetation properties of riparian forests. This information is critical for programs involved in the management, conservation, and ecological restoration of riparian habitats. Low‐cost and time‐efficient indices, such as the RCI, facilitate ecological condition assessments of riparian habitats not only by scientists but also by previously trained land managers and the general public.
We demonstrate that adjacent land‐use type affects the ecological condition of riparian habitats. We also show that scientists, land managers and the general public might be able to assess the ecological condition of riparian habitats, its diversity, its floristic composition and the structural complexity of vegetation through low‐cost and time‐efficient indices, and hence, design conservation, management and restoration strategies for riparian habitats.
I investigated the size, composition and persistence of the seed-bank in primary forests, secondary forests and old-fields in southern Mexico. I also assessed the contribution of the seed-bank to ...regeneration relative to other propagule sources. In all habitats, I removed by hand all plants and litter and excluded the seed-rain. For one year, I counted the number of plant species (5-50 cm tall) emerged and grouped them into different growth-forms: trees, shrubs, palms, herbs, woody lianas, epiphytes and hemi-epiphytes. A total of 95 species emerged. The seed-bank size, composition and persistence showed strong variation among successional stages. Emergence was low for primary and secondary forests, but high for old-fields (19, 26, and 68 plants per m
, respectively). Herbs were the most abundant in the seed-bank and palms the less. Time had a negative effect on seed-bank size in primary forests and old-fields; whereas for secondary forests size remained constant throughout the year. The number of emerged plants in different growth-forms changed significantly across time for all successional stages. Overall, the seed-bank provided a greater number of plants in old-fields relative to other propagule sources combined. The results showed that forest modification alters the input of propagules throughout the seed-bank for different plant growth-forms.
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