Consequences of forest fragmentation and conditions for biological invasions:
the case of Caribbean birds
Transformation rate of natural ecosystems due to human activities has recently increased. Habitat fragmentation and biological invasions are major threats on biodiversity, as both are main processes responsible for populations and species declines.
Despite a large body of literature focusing on the impact of fragmentation or biological invasions on species abundance and diversity, changes in ecological and evolutionary processes due to these two global changes remain poorly understood.
This project aims to assess effects of fragmentation on several attributes of individuals/populations in a set of bird species showing a gradual specialization on forest habitat :
- genetic diversity, due to demographic changes (smaller and more isolated populations)
- phenotypic quality of individuals (i.e. morphological, ornamental, immunological, physiological stress)
- host-parasite interactions
In addition, we will test two recent hypotheses explaining the success of biological invasions (the so-called enemy release hypothesis and the hypothesis of different immune defense strategies in invaders), and investigate some of their consequences for native species.
This project will be conducted in four territories: French Guiana, Guadeloupe, Martinique, and Montserrat. If these territories host a high endemic biodiversity, they go through real problems of forest loss and fragmentation as well as species introductions or invasions, mainly due to human activities and demographic growth.
In addition, to contribute to a better knowledge of ecological and evolutionary consequences of habitat fragmentation and biological invasions, the integrated approach of this project will produce valuable results for decision rules in nature and wildlife management frameworks.
The collaboration of scientific partners and partners concretely involved in local conservation plans ensures the integration of research and wildlife management.
Human activities have been transforming much of natural ecosystems in the world for a long time, but this process has recently accelerated. As habitat modifications due to human activities may be associated with changes in both interspecific interactions (competition, predation, parasitism ...) and abiotic factors, direction and strength of natural and sexual selection may be deeply altered. Therefore, there is particular urgency to investigate how these anthropogenic habitat changes affect biodiversity, not only to preserve it but also to predict how evolutionary trajectories of species will be affected.
Why studying the forest ecosystem ?
Forests have been the habitats the most affected by destruction, fragmentation or degradation. If temperate forests and woodlands are now regenerating in many areas after severe destruction and overexploitation in the past, tropical and subtropical forests are disappearing at an alarming rate. The interest in these biomes is also justified by the fact that they host the higher terrestrial biodiversity.
Why using birds as a biological model ?
Although birds are well studied models in temperate areas, ecological and evolutionary processes have been poorly studied in tropical birds. For instance, little is known about dispersal and movement responses to forest fragmentation in tropics. Moreover, it is sometimes assumed that birds are less affected by fragmentation at local geographic scales than other organisms because of their dispersal abilities. However, some elements suggest that fragmenting a landscape can have a greater impact on bird species persistence than previously thought, particularly in sub-tropical and tropical areas.
Why these territories ?
The Caribbean region is one of the 25 biodiversity hotspots and French Guiana belongs to one of the three major tropical wilderness areas. On the one side, these regions are simultaneously hosting a very high diversity of species but on the other side they have been subjects to severe losses of native habitats (notably rainforest) caused by activities of a dense and growing human population.
The high level of endemism, which is characterizing these territories, not only emphasizes the originality of local faunas and floras but also provide respective countries and territories with a critical responsibility to preserve biodiversity.
In the three island territories, landscape has firstly been deeply modified by agriculture development after colonization by Europeans (production of sugar, bananas, coffee, tobacco…). In Guadeloupe and Martinique, the second factor of land modification is the local demographic expansion (for instance, Martinique is currently the French region with the highest density after the Parisian region). In addition to (and probably in interaction with) habitat modification, native fauna and flora have suffered from the introduction/invasion of numerous species acting as competitors or predators.
In French Guiana, many habitats quoted as important for biodiversity at the regional scale (included forest habitats) are located within the coastal area. However, more than 80% of the population inhabits this coastal area, and demographic models predict that population will be multiplied by two over the next 20 years (INSEE predictions), especially in this part of the region. Most studies in French Guiana have focused on the Amazonian rainforest (which benefits from protection rules), but little is known on the effects of fragmentation in the coastal forest while it is the most perturbed area.
This project is divided in five workpackages (WP):
WP1 : Fragmentation and population genetic diversity
As fragmentation basically leads to smaller and more isolated forest patches, it should bring forest species to smaller populations exchanging fewer individuals. This change in demographic processes is expected to affect genetic diversity, which is a crucial feature of natural populations. Indeed, numerous studies showed that populations with lower genetic variability have a reduced evolutionary potential and experience a higher extinction risk. Studying population genetic structure will be an indirect way of assessing effects of fragmentation on demography of birds. We will appraise how landscape structure affects dispersal patterns.
WP2 : Fragmentation and phenotypic variability
WP3 : Fragmentation and host-parasite interactions
WP4 : Biological invasion and ecological immunology
WP5 : Ecological specialization and response to fragmentation