Acta Oecologica-International Journal of Ecology最新文献

The decline in species diversity within nutrient-enriched grasslands is commonly explained by a single hypothesis that often overlooks the potential interconnected roles of soil nutrients, light, and plant productivity. In a 2-year field experiment involving multiple nutrient additions (nitrogen, phosphorus, and potassium; NPK) conducted in an alpine meadow on the eastern Qinghai-Tibet Plateau, we investigated the simultaneous impact of three driving factors (soil nutrients, litter, and light) on species loss. Our findings show that the reduction in species richness can be attributed to belowground soil nutrient enrichment and aboveground light asymmetry. Specifically, the increase in soil nutrients following NPK addition directly contributed to the decline in species richness. Light limitation associated with an increase in the aboveground net primary productivity (ANPP) indirectly accelerates competitive exclusion, leading to species loss. The increased ANPP was primarily influenced by the greater proportion of the grass species Elymus nutans in the NPK-fertilized plots, highlighting the significant role of dominant species in restricting light availability.

Contrary to expectations, our results did not support the negative impact of litter on species richness. In summary, our findings indicate that interspecies competition for soil nutrients and light availability are the two primary drivers of species loss in alpine meadow communities. This insight has crucial implications for understanding the effects of nutrient enrichment on biodiversity, ecosystem functioning, and services in alpine meadows on the Qinghai-Tibet Plateau.

Arid and semiarid ecosystems display several environmental filters naturally restricting plant community composition. Such filters become more severe after some disturbance and may thus hamper the survival of young plants. The role of remnant trees in succession needs to be better understood to identify patterns and functional traits that might facilitate natural regeneration in drylands. This study evaluated the role of remnant trees in the succession process in the caatinga vegetation (Brazilian seasonally dry tropical forest), testing the effect of a typical tree, the juazeiro (Ziziphus joazeiro Mart.) in richness and abundance of seedlings in areas of abandoned pasture, in Northeastern Brazil. A perimeter was outlined around each plant (n = 20) with a diameter equivalent to each tree crown; all seedlings of woody species up to 0.5 m in height, within that perimeter, were collected and identified. Control areas with the same dimensions were delimited in adjacent locations (n = 20) without the influence of remnant trees, followed by the same data surveys. Mean species richness was of 7.8 ± 4.8 under the juazeiro canopies, compared to 2.3 ± 1.9 in the control areas. Species abundance was also greater under the presence of Z. joazeiro, with an average of 16.9 ± 4.8, against 4.1 ± 4.2 individuals in the controls. Among the abiotic factors evaluated, it is suggested that soil and air temperatures may show a greater influence on the recruitment of seedlings, benefiting natural regeneration under Z. joazeiro. Z. joazeiro ramnant trees appear to facilitate the natural regeneration of tropical drylands. We suggest considering the use of these plants as catalysts for the nucleation process in the restoration of the caatinga.

The management of plants and landscapes can affect the reproductive cycle of species through changes in morphology, temporal distribution of resources, and productivity, with ecological implications. In this study, we investigated the influence of management practices on the reproductive phenology and nectar availability of Cereus jamacaru DC, a columnar cactus native to Brazil managed by local people in the Caatinga dry forest. Our results reveal that the traditional management practices alter the quantitative and spatiotemporal distribution of resources (flowers, fruits, and nectar) of individuals of C. jamacaru in the studied Caatinga. All populations exhibited annual patterns of flowering and fruiting. However, individuals of the ex situ managed population showed a distinct temporal distribution pattern of flowering, with flower buds and flowers more regularly distributed throughout the reproductive period, compared to individuals of the in situ and unmanaged populations. Management practices differentially affected the production of flower buds, flowers, and fruits with a positive effect on fruit set in the in situ managed population. In addition, individuals of managed populations presented anticipation in the average date of the emission peaks of flower buds and ripe fruits. Individuals from the in situ managed population had available a greater volume of nectar with a higher sugar concentration per flower (twice as high) compared to the ex situ managed population and unmanaged population. The management practices seem to provide advantageous conditions for individuals of C. jamacaru since they allow higher availability of resources (flowers, nectar, and fruits) for a longer period in the Caatinga dry forest. Thus, management practices can prolong the temporal distribution of flowers and fruits, providing more resources for specialized pollinators (Sphingids) and dispersers (birds, reptiles), which are groups vulnerable to anthropic disturbances and climate changes in the Caatinga dry forest. These practices ultimately contribute to the maintenance of key ecological interactions of other species dependent on these vectors, benefiting the whole plant and animal community in the Caatinga dry forest.

In some species, females vary in the numbers of times they mate. While polyandry will always be beneficial to a male that mate with a previously mated female, the effect on female fitness is unclear. From females' perspective, variation in matedness can reflect adaptive differences in females’ requirements for mating or non-adaptive chance factors. Pollinating fig wasps have been considered to be mostly monandrous although polyandry has been confirmed in a number of species. Here we first show that the pollinating fig wasp, Platyscapa awekei, is polyandrous. Second, we show that intraspecific variation in female matedness may be explained best by chance encounters between males and receptive females. The mean number of offspring does not increase with polyandry. Nor is there evidence of sperm limitation. These observations rule out direct benefits to females. Despite evidence for multiply-mated females having mated with less compatible males, multiple mating is not combined with selective preference for more compatible males' sperm, ruling out indirect benefits. Therefore variation in female matedness seems to have no fitness benefit to females and from the females' perspective may be best explained by chance variation in encounter rates between males and receptive females.

Enhanced mammal functional diversity is crucial for forest ecological functioning. However, this group is affected by habitat degradation, such as mineral exploitation, which is a major threat worldwide. In these habitats, the maintenance of forest patches is important to support species diversity. Here, we addressed this knowledge gap by examining the functional diversity of medium-sized mammals among forest patches of different sizes in an area of approximately 3195 ha that is used for copper mining in the eastern Pará state, in the eastern Brazilian Amazon. In these patches, we also observed responses between mammal functional diversity and patch structural complexity. We used camera traps to survey the mammal fauna. We observed that large forest patches are associated with enhanced mammal functional diversity, mainly due to higher canopy closure and overstory tree density. In these habitats, species with functional attributes that allow resource partitioning may occur, which is important for habitat functioning. These findings have major implications for maintaining forest patch heterogeneity in mined areas, which is important for mammal functional diversity. Thus, management efforts in mining areas should explicitly include large forest patches to conserve mammal assemblages.

Slash-and-burn agriculture is a common practice in dry forests worldwide. Understanding the relative importance of different regeneration mechanisms following this disturbance provides insights into forest regeneration dynamics and resilience. We assessed differences in structural components, the relative contribution of vegetative and sexual reproduction, and the taxonomic composition of woody assemblages among different habitats in a Brazilian Caatinga dry forest after slash-and-burn agriculture. We assessed vegetation parameters (i.e., basal area, height, species richness, and the frequency of each regeneration mechanism) in recently abandoned fields, regenerating forest stands and old-growth forest stands. Overall, trees originates from root suckers accounted for at least 40% of the individuals, stems, and basal areas across the habitats. The structure of regenerating stands was similar to old-growth stands except for species composition, total number of roots, and number of primary roots. The aboveground basal area varied in total values, but not averages, among habitats, indicating a rapid recovery of aboveground biomass after slash-and-burn agriculture. Conversely, recently abandoned fields had higher belowground basal area and basal area of primary roots, revealing that the trees in these habitats emit more roots even with fewer individuals. There was a high degree of species turnover among the habitats, probably due to both species selection by farmers and environmental effects. Nevertheless, the dominant species presented both regeneration mechanisms across the habitats. Our findings thus show that the Caatinga dry forest regeneration considerably relies on the ability of woody plant species to emit root suckers in addition to sexual reproduction, which should be considered for better management practices as slash-and-burn agriculture is and will continue to be practiced.

Islands biogeography theory establishes that species richness and composition in islands result from ecological and evolutionary processes, such as immigration/emigration rate and the balance between speciation and extinction. Islands' geographic distribution, area, and distance from the mainland are important features in structuring communities of different taxonomic groups. Here, we aimed to evaluate the influence of geographic predictors on the variation of snakes' community composition. The study area encompassed 17 oceanic islands in the state of São Paulo, southeast Brazil. We recorded 40 species of snakes, with an average of 8.53 ± 8.11 species per island. We observed that islands closer to the mainland are more similar in snake composition, and more distant islands have a greater variation in composition among themselves. We verified a positive correlation between beta diversity and distance from the mainland, turnover component and distance from the mainland, nested component and distance among islands, and nestedness and island area. So, we conclude that the spatial pattern of island snake composition seems to be related to species dispersal. However, it can also be a relictual fauna pattern due to the isolation of populations due to rising sea level and the subsequent formation of the studied islands. Our results reinforces the pivotal role of geographic factors in shaping spatial patterns of insular communities.

Plants and phytophagous insects make up the highest terrestrial diversity on the planet, forming complex interspecific interaction networks. Interaction networks are an important tool to understand how ecological interactions shape plant-herbivore assemblages. In the present study, we tested the hypotheses that the plant species richness and vegetation structure (vegetation cover and vegetation height) (i) drive the richness and abundance of herbivorous insects and (ii) determines topological patterns (connectance, specialization and modularity) of plant-herbivore networks. We sampled ten different areas in the Neotropical savannas to assess those hypotheses and constructed plant-herbivore interaction matrices using species composition data. Plant-herbivore interaction networks comprised 298 plants of 60 species, 421 insects distributed in 96 morphospecies, and totalizing 218 interactions. We found that plant species richness positively influenced the species richness of herbivorous insects, whereas average vegetation height negatively affected the species richness of herbivorous insects. The abundance of herbivorous insects was negatively affected by plant species richness, and by vegetation height. Species richness and structure of plant communities also significantly affected network topological parameters. Network connectance was negatively influenced by plant richness and positively affected by vegetation cover. Besides, plant species richness positively influenced network modularity, whereas vegetation height negatively affected network modularity. However, the plant community diversity and vegetation structure did not affect network specialization. Our results show that both plant community diversity and vegetation structure in Neotropical savannas drive the structure of plant-herbivore interaction networks. Considering the current high rates of removal of native vegetation in Brazilian savannas, our findings indicate that the preserving this ecosystem is crucial for maintaining ecosystem services through plant-herbivore interaction networks.

Frugivorous birds are the primary seed dispersers for fleshy-fruited plants through defecation. In general, small-sized species disperse seeds across short distances from parental plants. However, multiple seeds or seeds of different plant species are frequently mixed in the fecal mass, because birds are prone to eat multiple fruits of a few plant species during foraging. This suggests birds deposit seeds as clumps in the field, causing inter- and intraspecific competition. However, the exact number of dispersed seeds for each defecation is very hard to estimate in field. It may also vary according to several variables, such as body size of birds and number of seeds per fruit. To clarify seed deposition patterns, we captured small frugivorous birds and collected the feces and regurgitations. The number of seeds excreted in fecal samples was investigated. From 2003 to 2019, a total number of 21518 seeds from 60 plant species were collected from 2214 birds of 17 species. Average number of seeds included in the fecal sample was 9.7 ± SD 18.4 (range: 1–340). The frequency of the number of excreted seeds was not normally distributed and the mode value was one in all cases and for five main dispersers. In most cases (64.8–74.5%), birds excreted a single seed. Furthermore, the effects of morphological traits of birds and plants on number of excreted seeds were analyzed using GLMM. The body mass of birds had a positive effect on the number of excreted seeds. However, fruit and seed weight exhibited negative effects, suggesting the number of excreted seeds is smaller when smaller birds eat larger fruits bearing larger seeds. The seed deposition pattern based on excretion of a single seed may avoid seed and seedling aggregation at local sites.

Seed arrival to degraded areas often represents a limiting factor to forest regeneration, but seed-dispersing birds able to move into such areas may help to overcome such constraint. As the number of degraded areas prone to regeneration is increasing in the tropics, it is important to know which bird species and associated traits make such spillover movements. We studied the interactions between frugivorous birds and eight plant species in contiguous degraded and secondary forest areas in a Brazilian land-bridge island, evaluating the potential of avian cross-habitat spillover to disperse seeds to degraded areas and thus contribute to their vegetation recovery. We recorded 21 and 17 bird species removing fruits in degraded areas and secondary forests, respectively. Avian communities dispersing seeds in both habitats are dominated by habitat generalist species. Visitation and fruit removal rates did not differ between the two habitats. Avian cross-habitat spillovers were more frequent from secondary forests to degraded areas than the reverse. A few bird species (Dacnis cayana, Elaenia flavogaster, and Turdus spp.) stood out in the spillover between habitats due to their generalist habitat occupancy and capacity for foraging in disturbed areas. We likewise identified the plants that most attracted birds (including an exotic palm, Livistona chinensis) so as to pinpoint the plant species that may occasionally be the focus of management actions to enhance the arrival of seeds to degraded areas. We conclude that the spillover dynamics reported herein shed some light on how tropical forest regeneration could benefit from native species’ spatial behaviour, offering a biological alternative to overcome practical issues, such as seed limitation in degraded environments.