| 1. |
- Aguirre, A., et al.
(författare)
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Variation in sexual expression in Jacaratia mexicana (Caricaceae) in southern Mexico : Frequency and relative seed performance of fruit-producing males
- 2007
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Ingår i: Biotropica. - 0006-3606 .- 1744-7429. ; 39:1, s. 79-86
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Tidskriftsartikel (refereegranskat)abstract
- Dioecy, the segregation of male and female structures among individuals, is widespread in tropical plants, encompassing 10-30 percent of species in some sites. In many cases, interindividual sex separation is not complete, as individual plants, although nominally dioecious, may produce both types of reproductive structures. A common form of this sexual variation is the production of female structures in otherwise male individuals, commonly referred to as fruiting males. Here we report the existence of fruiting males in the dioecious tropical tree Jacaratia mexicana (Caricaceae). We show that fruiting males can constitute up to 45 percent of all males in some populations of a tropical forest in Southern Mexico. In order to determine the functional significance of fruiting males for the breeding system of J. mexicana, we compared the relative performance of male- and female-borne seeds. Our results show that seeds from fruiting males are three times less likely to germinate and survive than seeds from female trees. Based on relative seed fitness data, and sex ratios in natural populations, we estimate that 6-15 percent of the genes contributed by fruiting males to the next generation are transmitted via ovules, meaning that morphological variation in gender is at least partially accompanied by functional gender variation. Finally, our seed fitness estimates for fruiting males suggest that fruiting males will not replace female plants in natural populations.
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| 2. |
- Asuk, Sijeh A., et al.
(författare)
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Impact of human foraging on tree diversity, composition, and abundance in a tropical rainforest
- 2023
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Ingår i: Biotropica. - : Wiley. - 0006-3606 .- 1744-7429. ; 55:1, s. 232-245
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Tidskriftsartikel (refereegranskat)abstract
- Tropical forest tree communities are structured by a range of large-scale drivers including elevation, certain high-impact anthropogenic activities (e.g., deforestation), and fires. However, low-impact human activities such as foraging may also be subtly but notably altering the composition of tropical forest tree communities. The study assessed the (i) differences in species diversity, patterns of relative abundance, and pairwise beta diversity between trees with edible and inedible fruits and seeds along an elevation gradient, and (ii) impact of human foraging on the forest tree communities in Oban Division of Cross River National Park, Nigeria. Fifteen permanent 40 by 40 m plots were established along an elevational gradient (120–460 m above mean sea level). All trees of 0.1 m diameter at breast height (dbh) and above were measured, identified, and, with the aid of structured questionnaires, classified into those with edible and inedible fruits/seeds. A total of 35 edible species with density of 128 stems/hectare and basal area of 11.99 m2/hectare, and 109 inedible species with density of 364 stems/hectare and basal area of 22.42 m2/hectare were sampled. However, the evenness of edible and inedible species was similar at pooled and plot levels. For inedible species, there was a positive relationship between pairwise beta diversity and elevation, and this was driven mainly by turnover. In contrast, edible species exhibited a non-significant trend between elevation and beta diversity. Thus, the study showed that human foraging of edible fruits may have subtly influenced patterns of species diversity and community structure in this tropical forest.
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| 3. |
- Bacon, Christine D., et al.
(författare)
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The seasonally dry tropical forest species Cavanillesia chicamochae has a middle Quaternary origin
- 2022
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Ingår i: Biotropica. - : Wiley. - 0006-3606 .- 1744-7429. ; 54:1, s. 91-99
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Tidskriftsartikel (refereegranskat)abstract
- We use DNA sequence data to understand the evolutionary history of the genus Cavanillesia (Malvaceae), with particular emphasis on C. chicamochae, an emblematic succulent-trunked tree endemic to seasonally dry tropical forests (SDTFs) of the Chicamocha Canyon of Colombia, South America. Based on field sampling of multiple individuals from different populations, we inferred a phylogeny calibrated into absolute time using robust macrofossil information. We show strong support for a monophyletic Cavanillesia chicamochae, with a mean stem age of 1.46 Ma. Two different mechanisms could explain its origin, either a late uplift age of the eastern cordillera or increased dryness of the Chicamocha Canyon during the Middle Pleistocene Transition. We also find marked genetic differentiation of its populations within the Chicamocha Canyon, likely driven by a combination of climate change and local landscape processes. Our results suggest that within northern inter-Andean SDTFs, as has been demonstrated in the central Andes, dispersal limitation leads to species and even population monophyly within individual valleys. The genetic differentiation of populations of C. chicamochae, together with the presence of other endemic and threatened species in the Chicamocha Canyon, calls for urgent management to conserve the unique biodiversity in the region. Abstract in Spanish is available with online material.
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| 4. |
- Chatzopoulos, Paschalis, et al.
(författare)
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Height-diameter allometry for a dominant palm to improve understanding of carbon and forest dynamics in forests of Puerto Rico
- 2024
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Ingår i: Biotropica. - : John Wiley & Sons. - 0006-3606 .- 1744-7429. ; 56:2
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Tidskriftsartikel (refereegranskat)abstract
- Tropical forests play a major role in the global carbon cycle but their diversity and structural complexity challenge our ability to accurately estimate carbon stocks and dynamics. Palms, in particular, are prominent components of many tropical forests that have unique anatomical, physiological, and allometric differences from dicot trees, which impede accurate estimates of their aboveground biomass (AGB) and population dynamics. We focused on improving height estimates and, ultimately, AGB estimates for a highly abundant palm in Puerto Rico, Prestoea acuminata. Based on field measurements of 1003 individuals, we found a strong relationship between stem height and diameter. We also found some evidence that height–diameter allometry of P. acuminata is mediated by various sources of environmental heterogeneity including slope and neighborhood crowding. We then examined variability in AGB estimates derived from three models developed to estimate palm AGB. Finally, we applied our novel height:diameter allometric model to hindcast dynamics of P. acuminata in the Luquillo Forest Dynamics Plot during a 27-year period (1989–2016) of post-hurricane recovery. Overall, our study provides improved estimates of AGB in wet forests of Puerto Rico and will facilitate novel insights to the dynamics of palms in tropical forests.
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| 5. |
- Cromsigt, Joris
(författare)
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Mammalian herbivores, grass height and rainfall drive termite activity at different spatial scales in an African savanna
- 2016
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Ingår i: Biotropica. - : Wiley. - 0006-3606. ; 48, s. 656-666
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Tidskriftsartikel (refereegranskat)abstract
- Termites have a large influence on ecosystem functioning. Understanding what drives termite activity patterns improves understanding of nutrient cycling, productivity, and heterogeneity in savannas. We present a mechanistic framework that relates the interactive effects of rainfall, grassland structure, large herbivore presence, and soil factors to termite activity. To test this framework, we used grass litterbags to monitor termite activity at ten sites across Hluhluwe-iMfolozi Park, South Africa. We assessed the effects of abiotic and biotic factors on termite activity at two scales: the large (landscape) scale, variation in bait removal among 300m2 plots that were distributed across the park and at the small (within-plot) scale (1-300m2). Half of our sites were located inside large herbivore exclosures to test for the effect of mammalian herbivore presence. At the landscape scale, termite grass removal declined towards higher rainfall and in the presence of mammalian herbivores. Removal did not depend on soil factors. At the small scale, removal declined with increasing grass height, particularly in the 1m surrounding the bait bag. Resource quality did not affect bait removal. We suggest that competition for forage drives the negative effect of mammalian herbivores on termites, whereas lower bait removal in taller swards may be due to direct negative effects from rainfall, fire and/or competition with free-living microbes. Ultimately, we suggest that the impact of termites on nutrient cycling is most pronounced when abiotic (rainfall) and biotic conditions (mammalian herbivory) limit grass removal by fire and decomposition by free-living microbes.
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| 6. |
- Derroire, Geraldine, et al.
(författare)
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The Effects of Established Trees on Woody Regeneration during Secondary Succession in Tropical Dry Forests
- 2016
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Ingår i: Biotropica. - : Wiley. - 0006-3606. ; 48, s. 290-300
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Forskningsöversikt (refereegranskat)abstract
- Understanding the mechanisms controlling secondary succession in tropical dry forests is important for the conservation and restoration of this highly threatened biome. Canopy-forming trees in tropical forests strongly influence later stages of succession through their effect on woody plant regeneration. In dry forests, this may be complex given the seasonal interplay of water and light limitations. We reviewed observational and experimental studies to assess (1) the relative importance of positive and negative effects of established trees on regeneration; (2) the mechanisms underlying these effects; and (3) to test the 'stress gradient hypothesis' in successional tropical dry forests. The effects of established trees on seed dispersal, seed survival, and seed germination-either through direct changes to moisture and temperature regimes or mediated by seed dispersers and predators-are mainly positive. The balance between positive and negative effects on seedling establishment is more complex and depends on the season and leaf phenology of both trees and seedlings. Seedling survival is generally enhanced by established trees mitigating dry conditions. Established trees have counteracting effects on water and light availability that influence seedling growth. The probability of a positive effect of established trees on seedling survival decreases with increased rainfall, which supports the stress gradient hypothesis. Priorities for future research are experiments to test for facilitation and competition and their underlying mechanisms, long-term studies evaluating how these effects change with ontogeny, and studies focusing on the species-specificity of interactions.
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| 7. |
- Doughty, Christopher E., et al.
(författare)
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What controls variation in carbon use efficiency among Amazonian tropical forests?
- 2018
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Ingår i: Biotropica. - : Wiley. - 0006-3606. ; 50:1, s. 16-25
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Tidskriftsartikel (refereegranskat)abstract
- Why do some forests produce biomass more efficiently than others? Variations in Carbon Use Efficiency (CUE: total Net Primary Production (NPP)/ Gross Primary Production (GPP)) may be due to changes in wood residence time (Biomass/NPPwood), temperature, or soil nutrient status. We tested these hypotheses in 14, one ha plots across Amazonian and Andean forests where we measured most key components of net primary production (NPP: wood, fine roots, and leaves) and autotrophic respiration (Ra; wood, rhizosphere, and leaf respiration). We found that lower fertility sites were less efficient at producing biomass and had higher rhizosphere respiration, indicating increased carbon allocation to belowground components. We then compared wood respiration to wood growth and rhizosphere respiration to fine root growth and found that forests with residence times <40 yrs had significantly lower maintenance respiration for both wood and fine roots than forests with residence times >40 yrs. A comparison of rhizosphere respiration to fine root growth showed that rhizosphere growth respiration was significantly greater at low fertility sites. Overall, we found that Amazonian forests produce biomass less efficiently in stands with residence times >40 yrs and in stands with lower fertility, but changes to long-term mean annual temperatures do not impact CUE.
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| 8. |
- Frisch, Andreas, et al.
(författare)
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Tree Species Composition Predicts Epiphytic Lichen Communities in an African Montane Rain Forest
- 2015
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Ingår i: Biotropica. - : Wiley. - 0006-3606. ; 47, s. 542-549
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Tidskriftsartikel (refereegranskat)abstract
- The ecology of many tropical rain forest organisms, not the least in Africa, remains poorly understood. Here, we present a detailed ecological study of epiphytic lichens in the equatorial montane rain forest of Bwindi National Park (331km(2)), Uganda. We evaluated all major lichen growth forms, including selected groups of crustose lichens. In 14 transects at elevations of 1290m to 2500m, we sampled 276 trees belonging to 60 species. We recorded all lichen species on each tree trunk between ground level and 2m above the ground, yielding 191 lichen species in 67 genera, with a mean of 4.7 species per tree. We used non-metric multi-dimensional scaling to separate epiphytic lichen assemblages according to tree species composition and elevation. Structural equation modeling indicated that elevation influenced tree species composition and that tree species composition largely determined lichen species composition. Thus, elevation acted indirectly on the lichen assemblages. Further studies examining factors such as bark properties and lichen colonization ecology may clarify what determines the association between tree species and lichen assemblages. The link between lichen assemblages and large-scale elevation patterns, as well as disturbance and regrowth histories, warrants further study. An analysis of lichen species composition on individual tree species that occur over large elevation ranges would distinguish the effect of tree species on lichen assemblages from the effect of elevation and thus climate. Our study highlights the limited extent of our knowledge of tropical epiphytic lichens.
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| 9. |
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| 10. |
- Gómez-Correa, Luisa F., et al.
(författare)
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Canopy tree mortality depends on the proportion of crown exposed to sunlight, but this effect varies with species' wood density
- 2023
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Ingår i: Biotropica. - 0006-3606 .- 1744-7429. ; 55, s. 1136-1147
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Tidskriftsartikel (refereegranskat)abstract
- Understanding what drives changes in tree mortality as well as the covariates influencing trees' response is a research priority to predict forest responses to global change. Here, we combined drone photogrammetry and ground-based data to assess the influence of crown exposure to light (relative to total crown area), growth deviations (relative to conspecifics), tree size, and species' wood density (as a surrogate for light-demanding and shade-tolerant life-history strategies) on the mortality of 984 canopy trees in an Amazon terra firme forest. Trees with lower wood density were less prone to die when their proportion of crown was more exposed to sunlight, but this relationship with relative crown exposure weakened and slightly reversed as wood density increased. Trees growing less than their species average had higher mortality, especially when the species' wood density decreased. The role of wood density in determining the survival of canopy trees under varying light conditions indicates differential responses of light-demanding versus shade-tolerant species. Our results highlight the importance of accounting for life-history strategies, via plant functional types, in vegetation dynamic models aiming to predict forest demography under a rapidly changing climate. Abstract in Spanish is available with online material.
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