Impacts des mammifères néotropicaux sur les graines

Seeds dispersal and predation by mammals are two key processes affecting the dynamics of plant communities. Neotropical rainforests, which are of great complexity, have many different relationships involving plant propagules and mammals. Dispersal allows the seed to escape competition and predation, to colonize new sites and to establish in favorable micro-sites. Seed predation reduces the number of seeds able to germinate, can affect dispersal of the remaining seeds and is one of the mecanisms that maintain a high plant species diversity in tropical rainforests. Didelphimorphs and chiropteras are very good dispersers that have a primary role in forest regeneration. Seed predation is very rare in these taxons. Primates, the most studied group on this subject, are also very good dispersers, sometimes predators, and possess an extremely diverse diet. Ungulates can be either dispersers, predators, or both. Their importance is due to their ability to consume generally larger seeds than other mammals. Rodents do not show a net profile and are distinctive by their synzoochore behaviour, consisting of hiding seeds and feeding on them later. An important part of cached seeds can be forgotten and later germinate. The role of carnivores in seed predation or dispersal is poorly known but a few studies show that they could be effective dispersers. Key words: dispersal, mammal, neotropical, predation, seed, zoochory.La dispersion et la prédation des graines par les mammifères sont deux processus-clés de la dynamique des communautés végétales. Les forêts humides néotropicales, dont la grande complexité est reconnue, présentent un éventail très vaste de relations mammifèrespropagules des plantes. La dispersion permet aux graines d’échapper à la compétition, à la prédation, de coloniser de nouveaux sites et de s’établir dans des micro-sites favorables. La prédation diminue le nombre de graines candidates à la germination, peut affecter la dispersion des graines restantes et constitue un mécanisme de maintien de la grande diversité végétale en forêt tropicale. Les didelphimorphes et les chiroptères sont de très bons disperseurs qui ont un rôle primordial dans la régénération de la forêt. Les cas de prédation des graines dans ces deux taxons sont très rares. Les primates, taxon le plus étudié à ce jour sur le sujet, sont également de très bons disperseurs, parfois prédateurs, qui possèdent une diète extrêmement variée. Les ongulés peuvent être disperseurs ou prédateurs, l’un n’excluant pas l’autre. Leur importance se situe dans leur habilité à consommer des graines en général plus grosses que les autres mammifères. Les rongeurs ne présentent pas un profil net et se distinguent par leur comportement de synzoochorie, consistant à cacher des graines afin de s’en nourrir plus tard. Une part importante de ses graines sera cependant oubliée et candidate à la germination. Le rôle des membre de l’ordre des carnivores est très peu connu, mais quelques études effectuées montrent qu’ils peuvent être d’efficaces disperseurs. Mots-cles: dispersion, graine, mammifère, néotropical, prédation, zoochorie

Impacts des mammifères néotropicaux sur les graines

Seeds dispersal and predation by mammals are two key processes affecting the dynamics of plant communities. Neotropical rainforests, which are of great complexity, have many different relationships involving plant propagules and mammals. Dispersal allows the seed to escape competition and predation, to colonize new sites and to establish in favorable micro-sites. Seed predation reduces the number of seeds able to germinate, can affect dispersal of the remaining seeds and is one of the mecanisms that maintain a high plant species diversity in tropical rainforests. Didelphimorphs and chiropteras are very good dispersers that have a primary role in forest regeneration. Seed predation is very rare in these taxons. Primates, the most studied group on this subject, are also very good dispersers, sometimes predators, and possess an extremely diverse diet. Ungulates can be either dispersers, predators, or both. Their importance is due to their ability to consume generally larger seeds than other mammals. Rodents do not show a net profile and are distinctive by their synzoochore behaviour, consisting of hiding seeds and feeding on them later. An important part of cached seeds can be forgotten and later germinate. The role of carnivores in seed predation or dispersal is poorly known but a few studies show that they could be effective dispersers. Key words: dispersal, mammal, neotropical, predation, seed, zoochory.La dispersion et la prédation des graines par les mammifères sont deux processus-clés de la dynamique des communautés végétales. Les forêts humides néotropicales, dont la grande complexité est reconnue, présentent un éventail très vaste de relations mammifèrespropagules des plantes. La dispersion permet aux graines d’échapper à la compétition, à la prédation, de coloniser de nouveaux sites et de s’établir dans des micro-sites favorables. La prédation diminue le nombre de graines candidates à la germination, peut affecter la dispersion des graines restantes et constitue un mécanisme de maintien de la grande diversité végétale en forêt tropicale. Les didelphimorphes et les chiroptères sont de très bons disperseurs qui ont un rôle primordial dans la régénération de la forêt. Les cas de prédation des graines dans ces deux taxons sont très rares. Les primates, taxon le plus étudié à ce jour sur le sujet, sont également de très bons disperseurs, parfois prédateurs, qui possèdent une diète extrêmement variée. Les ongulés peuvent être disperseurs ou prédateurs, l’un n’excluant pas l’autre. Leur importance se situe dans leur habilité à consommer des graines en général plus grosses que les autres mammifères. Les rongeurs ne présentent pas un profil net et se distinguent par leur comportement de synzoochorie, consistant à cacher des graines afin de s’en nourrir plus tard. Une part importante de ses graines sera cependant oubliée et candidate à la germination. Le rôle des membre de l’ordre des carnivores est très peu connu, mais quelques études effectuées montrent qu’ils peuvent être d’efficaces disperseurs. Mots-cles: dispersion, graine, mammifère, néotropical, prédation, zoochorie

Crescimento de plantulas da especie invasora Calotropis procera em solos de campos rupestres ferruginosos e floresta seca sazonal

The present study evaluated the growth, biomass allocation and nutrient content in seedlings of the invasive and exotic especies Calotropis procera (Aiton) W.T. Aiton (Apocynaceae), cultured in greenhouse, in soils from two different ecosystems: ironstone rupestrian fields (Canga) of Brumadinho, Minas Gerais; and seasonally dry forest (Caatinga), of Serra Talhada, Pernambuco. Seedlings from the Canga treatment were significantly higher in concern to stem length, leaf biomass and total biomass. In respect to nutrient content there were higher phosphorus, iron and zinc levels in the seedlings from the Canga treatment. The iron accumulation indicates the capacity of C. procera to tolerate high levels of iron, which is characteristic of Canga soils. In the Caatinga treatment there was a higher root/ shoot ratio and a higher potassium accumulation in the plant tissues. The obtained results suggest that C. procera displays a good adaptation to the edaphic conditions of the Canga treatment, which indicates an invasive potential towards the Canga ecosystem. Key words: Caatinga, Calotropis procera, Canga, early growth, invasion.O presente estudo avaliou o crescimento, a alocação de biomassa e os teores de nutrientes em plântulas da espécie exótica e invasora Calotropis procera (Aiton) W.T. Aiton (Apocynaceae), cultivadas em casa de vegetação, em solos provenientes de dois ecossistemas distintos: campo rupestre ferruginoso (Canga, Brumadinho, Minas Gerais) e floresta seca sazonal (Caatinga, Serra Talhada, Pernambuco). Plântulas do tratamento Canga foram significativamente maiores em relação ao comprimento do caule, biomassa de folhas e biomassa total. Em relação aos teores de nutrientes, houve maior teor de fósforo, ferro e zinco nos tecidos de plântulas do tratamento Canga. O acumulo de ferro indica a capacidade de C. procera em tolerar os altos teores de ferro característicos dos solos de Canga. No tratamento Caatinga, houve uma maior razão raiz-ramo e maior acúmulo de potássio em seus tecidos. Os resultados obtidos sugerem que C. procera demonstra boa adaptação às condições dos solos do tratamento Canga, indicando um potencial para invasão no ecossistema de Canga. Palavras-chave: Caatinga, Calotropis procera, Canga, crescimento inicial, invasão biológica

Climatic, Ecophysiological, and Phenological Controls on Plant Ecohydrological Strategies in Seasonally Dry Ecosystems

Large areas in the tropics and at mid-latitudes experience pronounced seasonality and inter-annual variability in rainfall and hence water availability. Despite the importance of these seasonally dry ecosystems (SDEs) for the global carbon cycling and in providing ecosystem services, a unifying ecohydrological framework to interpret the effects of climatic variability on SDEs is still lacking. A synthesis of existing data about plant functional adaptations in SDEs, covering some 400 species, shows that leaf phenological variations, rather than physiological traits, provide the dominant control on plant-water-carbon interactions. Motivated by this result, the combined implications of leaf phenology and climatic variability on plant water use strategies are here explored with a minimalist model of the coupled soil water and plant carbon balances. The analyses are extended to five locations with different hydroclimatic forcing, spanning seasonally dry tropical climates (without temperature seasonality) and Mediterranean climates (exhibiting out of phase seasonal patterns of rainfall and temperature). The most beneficial leaf phenology in terms of carbon uptake depends on the climatic regime: evergreen species are favoured by short dry seasons or access to persistent water stores, whereas high inter-annual variability of rainy season duration favours the coexistence of multiple drought-deciduous phenological strategies. We conclude that drought-deciduousness may provide a competitive advantage in face of predicted declines in rainfall totals, while reduced seasonality and access to deep water stores may favour evergreen species. This article has been contributed to by US Government employees and their work is in the public domain in the USA

Calotropis procera: um levantamento preliminar sobre as suas capacidades de fitoextração no Brasil

Calotropis procera (Apocynaceae) is a non-native species that has its origin in Africa and Asia, but was introduced into the northeastern region of Brazil in the beginning of last century. In some areas, the dry biomass of C. procera is used as animal feed. However, previous studies indicated that the species is capable of accumulating many chemical elements. On the other hand, it could also mean that this species may be used for phytoremediation. Hence, we used neutron activation analysis, k0-method, to test the capability of the leaves of C. procera to accumulate trace elements. The study was carried out in two distinct areas (polluted and non-polluted) in the State of Pernambuco, Brazil. Our results indicate that new elements can be added to the list of elements taken up by C. procera, thus contributing to the understanding of the biology of this plant species as an accumulator of trace elements. Some elements, such as Ba and Sr, have higher concentrations in the non-polluted areas than in polluted areas. Thus, the presence of many trace elements in C. procera indicates that its use as animal feed should be viewed with extreme caution. However low levels of these trace elements in C. procera do not indicate that this species is a hyper-accumulator plant.Key words: phytoremediation, biological invasion, invasive species, Pernambuco.Calotropis procera (Apocynaceae) é uma espécie exótica originária da África e Ásia tropical, introduzida na região nordeste do Brasil no início do século passado. Em algumas regiões do Brasil e do mundo, a biomassa seca de C. procera é utilizada como alimento forrageiro para animais. Entretanto, muitos estudos indicam que essa espécie é capaz de acumular diversos elementos químicos. Isso pode significar que a espécie também pode ser utilizada em processos de fitorremediação. Dessa forma, foi realizada uma análise de ativação neutrônica, método k0, para testar a capacidade das folhas de C. procera acumularem elementos-traço. O estudo foi realizado em duas áreas distintas (poluídas e não poluídas) no estado de Pernambuco, Brasil. Nossos resultados indicam que novos elementos podem ser adicionados à lista de elementos-traço absorvidos por C. procera, contribuindo para o entendimento da biologia dessa espécie como acumuladora de elementos-traço. Alguns destes, tais como Ba e Sr, ocorreram em maiores concentrações em áreas não-poluídas em comparação com áreas poluídas. Dessa forma, o uso de C. procera como ração animal deve ser vista com extrema cautela. Entretanto, as baixas concentrações desses elementos-traço não sugerem que C. procera seja uma hiperacumuladora.Palavras-chave: fitorremediação, invasão biológica, espécie invasora, Pernambuco

Biodiversity recovery of Neotropical secondary forests

Old-growth tropical forests harbor an immense diversity of tree species but are rapidly being cleared, while secondary forests that regrow on abandoned agricultural lands increase in extent. We assess how tree species richness and composition recover during secondary succession across gradients in environmental conditions and anthropogenic disturbance in an unprecedented multisite analysis for the Neotropics. Secondary forests recover remarkably fast in species richness but slowly in species composition. Secondary forests take a median time of five decades to recover the species richness of old-growth forest (80% recovery after 20 years) based on rarefaction analysis. Full recovery of species composition takes centuries (only 34% recovery after 20 years). A dual strategy that maintains both old-growth forests and species-rich secondary forests is therefore crucial for biodiversity conservation in human-modified tropical landscapes. Copyright © 2019 The Authors, some rights reserved