20 / 76
20
To understand the rising risk to migratory species, it is impera-
tive to begin with an overview of global changes and declines in
biodiversity worldwide, as this pattern is an even greater threat
to migratory species than to most non-migratory species.
The “Big Five” primary causes of biodiversity loss in general are
habitat destruction/fragmentation, overharvesting/poaching,
pollution, climate change and introduction of invasive species.
These impacts affect virtually all species on the planet, both
sedentary and migratory alike.
There are several global scenarios of biodiversity but all consistently
point to further biodiversity loss across the next century, however
at differing rates (Perira
et al.
, 2011). Scenarios of future habitat
loss by the GLOBIO 3.0 model have been used extensively by vari-
ous agencies of the United Nations, the Organization for Econom-
ic Co-operation and Development (OECD) and the Convention on
Biological Diversity (CBD) (see
www.globio.info), and suggest, like
most other models, a substantial increase in both the rate and ex-
tent of biodiversity loss over the next four decades (Fig. 5a-e).
The CBD estimates that the accelerating rate of deforestation,
which has taken place over the last century, has contributed to
reducing the abundance of forest species by more than 30 per
cent. The rate of species loss in forest regions is considerably
faster than in other ecosystems. Between now and 2050, it is
projected that there will be a further 38 per cent loss in abun-
dance of forest species (UNEP-GLOBIO 2008).

Habitat loss and global biodiversity loss
2000–2050
Figure 4:
A photographic demonstration of what Mean Species Abundance (MSA) means in terms of
changes in the landscape and its wildlife (UNEP, 2009).
Photographic impression of mean species abundance indicator
Forest
Mean abundance of
original species
Grassland
100%
0%
Pristine forest
Original species
Selective logging
Extensive use
Secondary vegetation Plantation
Subsistence agriculture Intensive agriculture