Revues bibiographiques

The effects of selective logging on the functional diversity and composition of tropical tree communities

KREUS Robin and BEROUJON Solene, proposed by Geraldine DERROIRE

There is an urgent need to evaluate the potential of conservation of tropical logged forest. Here, we aim to provide a synthesis on the functional responses of tropical tree communities to selective logging in terms of functional diversity and composition. Selective log-ging didn’t modify functional richness but lead to higher functional evenness. The functional composition is modified from conservative to fast acquisitive traits, which implies a shift from shade-tolerant species to pioneer-species. Those changes differ depending of the time considered after logging and are led by the recruitment more than survival or mortality. They result mainly from biotic factor (e.g. light) but also biotic factor (e.g. lianas). Spatial and temporal scales have to be taken into account to interpret and compare results. For a better conservation of functional diversity, single large gaps should be preferred to fewer smaller gaps when exploiting forests. More research is needed on root trait in response to soil compaction.

Article complet

The effect of climate change on plant mutualistic interactions

CALDERON -SANOU Irene and ISASA Emilie, proposed by Céline LEROY

Mutualisms play a major role in ecosystems functioning and maintenance. Plant mutualisms are crucial for plant nutrition, reproduction and survival. Climate change, including increased atmospheric CO2 levels and temperatures, and changes to precipitation patterns, are already affecting biological systems in different ways. These changes may affect the evolution and maintenance of mutualisms that are temporally and spatially dynamic. Some mutualisms will be disrupted, while others will persist depending on the nature of environmental changes. Here, we review the effects of climate change on plant mutualisms. We focused on two plant mutualisms: firstly ant-­‐plant symbiotic mutualisms, implicated in plant protection and nutrition; secondly plant-­‐pollinator transitory mutualisms, implicated in pollen transportation for plant reproduction. We found that drought promotes ant–plant symbioses. Water stress increases herbivory and therefore plants host and feed ant colonies as defense against herbivores. For plant-­‐pollinator mutualisms, phenological shifts to plants and their pollinators are leading to a spatial and temporal mismatch, causing mutualism breakdowns. Modeling, together with life-­‐history traits and population ecology has allowed prediction of pollination systems based on interaction characteristics. Generalists are likely to maintain the functioning of pollination in the community by shifting partners, while specialists are more likely to become extinct if mis-­‐ matches are significant. These examples illustrate two possible outcomes of mutualisms under climate change, but many other mutualisms need to be taken in consideration to understand how ecosystems will respond to global changes.

Article complet

Pollination and dissemination in the genus Cecropia: contrasts between different species

MONJOIN Thomas and TCHANA WANDJI Ruth, proposed by Patrick HEURET

Cecropia (Cecropiaceae) is a genus of 61 species found in the Neotropics. It is a typical pioneer tree, abundant in light gaps and in disturbed areas like secondary forests and varies considerably in size and distribution. Given that they are considered a keystone food supply for frugivorous animals, they have various different pollination and dispersal mechanisms. The aim of this report is to describe the phenology, pollination and seed dispersal of Cecro-pia species and to describe the limits of our knowledge on this subject. Although they are generally anemophilous, they also undergo entomophily. Studies about Cecropia seed dispersal and animals’ diets in Neotropics have found dissemination principally carried out by birds, bats, monkeys, other mammals, even fishes, and water. However, further study is required to better understand dispersal mechanisms (secondary dispersion) of Cecropia.

Article complet

The multiple functions of tree bark

DUCATEZ-BOYER Laura and MAJOURAU Pauline, proposed by Bruno CLAIR

Bark provides many functions for trees. Bark plays an essential role in transporting photosynthetic products in plant tissues. Bark is also crucial to the mechanics of the stem. Furthermore, bark is involved in defense against herbivory, protects against fire, and provides insulation in cold conditions. Other functions related to storage of water, metabolic regulation, or wound healing contributes as well to the life of trees. These functions of the bark are linked to its complex structure. Bark structure is well known and is defined as the whole tissue beginning from the vascular cambium and running until the rhytidome. A high variability of bark tissues morphology exists between species, which may indicate its importance in tree processes and highlights its role in plant ecological strategies.

Article complet

The effects of urbanization on ant communities

DEROISY Antoine and AUCOURD Marie, proposed by Jérôme ORIVEL

This review presents the effects of urbanization on ant communities. We found habitat fragmentation and land cover changes, urban heat effect, and the pollution as the main effects of urbanization. These factors impact ant communi-ties’ species richness, abundance, and composition. Although some research has been conducted, questions still remain relating to influences of urbanization on ant communities. Species richness and abundance of ant communities respond differently according to a range of parameters: the degree of urban disturbance, the scale on which the study is con-ducted and community composition including species of ants with pre-adapted traits. Species richness and abundance of ants can increase up to an intermediate level of urbanization, from where it begins to decline. The size of the studied area will also influence richness. Most importantly, composition will vary, with native or non-native species becoming dominant and sometimes invasive. Interestingly, the modification of the composition does not always affect the species richness or abundance.

Article complet

How mycorrhizal symbiosis shaped Angiosperm evolution

HATTERMANN Tom, proposed by Heidy SCHIMANN

The contribution of mycorrhiza to plant performance, distribution and diversity is well documented. This contribution underlines the intricate relationship between Plants and Fungi functionality. Yet, how such a symbiosis shaped Angiosperm evolution remains poorly understood due to the difficulties of obtaining retrospective evidence. Biotic interactions are consistently evolving through time and space, but mycorrhizal symbiosis is remarkably stable over the macroevolutionary time-scale. Based on a biogeographical and functional approach, we propose here an overview of the potential effect of a fungal-partner on the evolution of plant strategies. We first review some generalities about mycorrhiza. Then, we discuss phylogenetic and climatic patterns of root traits to justify bidirectional control. By an integrative approach to plant functionality, we propose a debate on the potential influence of mycorrhiza and other fungi on foliar trait plasticity and evolution. Next, we claim the importance of considering ontogeny in ecosystem dynamics and functionality studies. Following this, we address the evolutionary profile of two emblematic Angiosperm groups: mycoheterotrophic plants from a trait point of view and Fabaceae from an ecosystem point of view. Plants have an extensive cortège of associated microorganisms making it work as a whole. Plasticity of the association and multidirectional control could be the main catalysts for Angiosperm success through evolutionary time. This coordination interferes with the traceability of mycorrhizal contribution to Angiosperm evolution, which could have shaped it in many ways. By further extending our knowledge on the communication between mutualistic microorganisms and plants, new research will increase our understanding of how mycorrhizal symbiosis has shaped Angiosperms genetically, functionally and morphologically through time.

Article complet

Origins and maintenance of biological diversity: Current opinions and ongoing issues, with an emphasis on Neotropical forests and the Amazon basin.

DUCOURET Emilie and PAGE Nino, proposed by Eric MARCON

The Amazon Basin is by far one of the most diverse places on Earth. Over decades, many theories were built to understand how this biological diversity has appeared and is maintained. In this work, we try to synthesize the most pertinent, out of the many existing theories. We focus on species richness as a basic measure of biological diversity. Moreover, we emphasise on tree diversity, for they constitute the basic level of tropical rainforests trophic webs. The first section discusses the processes that allowed so many species to rise. These processes involve biotic (vicariance, migration, coevolution) or abiotic (climatic or hydrographic variation and orogenesis) mechanisms. There is still no consensus about which of these drivers had the most influence on the Amazonian evolutionary history, and even less about when diversification rates were the highest. Second section emphasises on the theories about processes that promote species coexistence. They describe deterministic or stochastic (rather, mixed) mechanisms. The first involves niche-based theories and density dependence due to pathogens. The second encompasses Hubbell’s neutral theory and Chesson’s general theory of competition in variable environment. To measure the importance of these theories is difficult. They all have arguments in favour, depending at which scale one is looking. Nowadays, efforts to integrate these theories together in appropriate spatio-temporal frame-works are particularly needed.

Article complet

DiaryTous les événements

News items Toutes les brèves