Download status of biodiversity - ENVIS Centre On Avian Ecology

The status of biodiversity
Marleen De Troch
Ghent University
Marine Biology Section
Krijgslaan 281/S8
Tel. 09/264 85 20
[email protected]
high number of extinctions:
e.g. in the last 4 centuries:
115 birds, 58 mammals, 100 reptiles, 64 amphibians
BUT
1.4 million species described
= fraction of total species on earth
estimates of total diversity: 5-50 million species
most what is out there is unknown to us
this deficiency = Linnaean shortfall
opportunity for field biologists
current trend and specialisation of taxonomists:
Linnaean shortfall will remain for some time
majority of undiscovered animals are thought to be
insects, spiders, other invertebrates
only 30% of taxonomists specialised in these groups
Entomologists
16%
Chordates
3%
Insects
55%
Chordate
systematists
33%
Status of marine biodiversity
marine realm is still a great biological frontier
< 10 % of the world’s oceans is adequately sampled
for biodiveristy purpose
even moderately rare species are easily missed (unknown)
dominant species: Homo sapiens
utilize 20 - 40 % of total primary production of terrestrial ecosystems
80 % of marine fish production
Geographic variation of biodiversity
geographic patterns of biodiversity central to
biogeography and conservation biology
3 most relevant:
1. species diversity increase towards the equator
systems at lower latitude:
higher local (alpha) and between-system (beta) diversity
2. islands, mountain tops, isolated systems:
species diversity increase with area and decrease with isolation
3. endemicity (relative number of unique species)
higher for larger and more isolated regions
variation in geographic ranges
towards the equator:
geographic ranges tends to decrease in size
tighter packing of species
higher species richness
geographic ranges not randomly distributed across the globe
but concentrated in particular regions:
hot spots
Hot spots
geographic co-occurence of many species
or
a site/region with an unusually high number of local endemics
= restricted - area species
hot spots of high endemicity:
most relevant to conserving biodiversity
Terrestrial hot spots
patterns of diversity and endemicity
important info for location and ultimately protection
of rare and endangered species
two important questions remain:
(1) how well can we predict the intensity and location
of hot spots for a particular taxonomic group?
(2) to what degree do different taxon-specific hot spots overlap?
Terrestrial hot spots
extinctions more likely for species with smaller ranges:
conservation of restricted-area species is priority
reliable estimates of diversity of some easily observable taxa
e.g. birds
International Council for Bird Preservation:
areas containing the breeding ranges of
at least 2 restricted-range species as
endemic bird areas (EBAs)
Terrestrial hot spots
EBAs (endemic bird areas) not randomly distributed
but concentrated in the tropical regions
high disproportionate number of EBAs occur on islands
islands cover < 10 % of the earth’s area
nearly half of all EBAs are insular
answer to first question:
at least for one well-studied group of terrestrial vertebrates
intensivity of avian hot spots is quite high
total area occupied by all EBAs:
6.5 million km2
just < 5% of world’s total land area provides breeding habitat
for a majority of its most threatened bird species
second question:
to what degree do avian hot spots overlap
with those of other animals and plants?
Birds
Central America:
areas of endemism of birds correspond
closely with reptiles and amphibians
less with areas of endemism of butterflies
Reptiles and amphibians
Butterflies
Africa:
areas of endemism are similar for amphibians and mammals,
birds and plants have additional hot spots
Birds
Mammals
Amphibians
Plants
most of biogeographical knowledge
comes from terrestrial studies
and some of freshwater systems
little is known about marine systems:
logistic challenges:
underwater and especially deep-water studies
> 70 % of earth’s surface: covered by oceans
half of world’s marine water are > 3000 m deep
max. benthic diversity between 2000 and 3000 m depth
below these depths:
diversity
but endemicity
key reasons for high endemicity in deep-sea:
isolated nature of the deepest areas
trench, seep, hydrothermal vents=
marine analogues of isolated oceanic islands
hadal communities (below 6000 m)
1% of the ocean’s benthic area
distributed among highly disjunct sites
e.g. trenches
trenches:
50-90%
endemicity
hydrothermal
vents
and
cold seep
island-like systems
diversity low but
endemicity high
hydrothermal vents
discovered in 1977
1 new phylum, > 14 new families, 50 new genera
mollusks, polychaetes, arthropods
93% of species described from vents
90% restricted to vent habitats
high distinctness and endemicity of vent communities:
derives from 3 characteristics:
(1) isolation
(2) antiquity (existed throughout Phanerozoic,
time for evolutionary divergence)
(3) special adaptations required to live under high pressure,
chemically reducing and metal-rich environment
(chemosynthetic food chain rather than photosynthetic)
Geography of extinctions
historical record of extinctions:
important info for understanding the ongoing biodiversity crisis
many historical extinctions co-occured with
waves of human colonization and development
high number of extinctions
occurred on islands
reasons for insular extinctions:
mostly related to the isolation
and the ecological naïveté of insular biota
2/3 of historical extinctions of insular birds were caused
directly or indirectly by introduced mammals
fragility of insular biota derived from their isolation:
e.g. plants flourish without evolving defenses against herbivores
introduction of exotic species:
wave of extinctions
Species introductions: ecology and geography of invasions
magnitude of the problem:
frequency and diversity of anthropogenic introductions
of exotic species are enormous
more than plate tectonics or glacial cycles, invasions had
a homogenizing effect on the world’s biota
species introductions have transformed all types of ecosystems:
oceanic islands, isolated mountaintops to tropical rain forests
and the far reaches of the Antarctic
Effects of invasions on native species
many different mechanisms:
introduced species can compete with native species
introduced species can prey on native species
rats: often introduced and are important predators
by preying on ground-nesting birds and reptiles
decimated many endemic species
effect of introduced rats on species diversity of native insular reptiles
Current patterns of endangerment
mammals
Hunting,
collecting etc.
49%
habitat
destruction
50%
introduced
species
49%
mollusks
habitat
destruction
60%
Hunting,
collecting etc.
26%
Habitat loss and fragmentation
an example from tropical seagrass beds