The status of biodiversity

Marleen De Troch

Ghent UniversityMarine Biology Section

Krijgslaan 281/S8Tel. 09/264 85 20

marleen.detroch@UGent.be

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 speciesmost what is out there is unknown to usthis 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 beinsects, spiders, other invertebrates

only 30% of taxonomists specialised in these groups

Insects55%

Entomologists16%

Chordates3%

Chordate systematists

33%

Status of marine biodiversity

marine realm is still a great biological frontier

< 10 % of the world’s oceans is adequately sampledfor biodiveristy purpose

even moderately rare species are easily missed (unknown)

dominant species: Homo sapiensutilize 20 - 40 % of total primary production of terrestrial ecosystems

80 % of marine fish production

Geographic variation of biodiversity

geographic patterns of biodiversity central tobiogeography and conservation biology

3 most relevant:

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

1. species diversity increase towards the equatorsystems at lower latitude:higher local (alpha) and between-system (beta) diversity

variation in geographic ranges

towards the equator:geographic ranges tends to decrease in size

tighter packing of specieshigher 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

a site/region with an unusually high number of local endemics= restricted - area species

or

hot spots of high endemicity:most relevant to conserving biodiversity

Terrestrial hot spots

patterns of diversity and endemicityimportant info for location and ultimately protection

of rare and endangered species

two important questions remain:

(1)how well can we predict the intensity and locationof hot spots for a particular taxonomic group?

(2) to what degree do different taxon-specific hot spots overlap?

Terrestrial hot spots

reliable estimates of diversity of some easily observable taxae.g. birds

International Council for Bird Preservation:

areas containing the breeding ranges ofat least 2 restricted-range species as

endemic bird areas (EBAs)

extinctions more likely for species with smaller ranges:conservation of restricted-area species is priority

Terrestrial hot spots

EBAs (endemic bird areas) not randomly distributedbut concentrated in the tropical regions

high disproportionate number of EBAs occur on islands

islands cover < 10 % of the earth’s areanearly 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 habitatfor a majority of its most threatened bird species

second question:to what degree do avian hot spots overlapwith those of other animals and plants?

Central America:areas of endemism of birds correspondclosely with reptiles and amphibians

less with areas of endemism of butterflies

Birds Reptiles and amphibians

Butterflies

Africa:areas of endemism are similar for amphibians and mammals,

birds and plants have additional hot spots

Birds Amphibians

Mammals Plants

most of biogeographical knowledgecomes 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 oceanshalf 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 sitese.g. trenches

trenches:50-90%

endemicity

hydrothermalventsand

cold seep

island-like systemsdiversity low butendemicity high

hydrothermal ventsdiscovered in 1977

1 new phylum, > 14 new families, 50 new genera

mollusks, polychaetes, arthropods93% 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 extinctionshistorical record of extinctions:

important info for understanding the ongoing biodiversity crisis

many historical extinctions co-occured withwaves of human colonization and development

high number of extinctions occurred on islands

reasons for insular extinctions:

mostly related to the isolationand the ecological naïveté of insular biota

2/3 of historical extinctions of insular birds were causeddirectly 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 introductionsof exotic species are enormous

more than plate tectonics or glacial cycles, invasions hada 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 reptilesdecimated many endemic species

effect of introduced rats on species diversity of native insular reptiles

Current patterns of endangerment

mammals

mollusks

Hunting,collecting etc.

49% introducedspecies49%

habitatdestruction

60%

habitatdestruction

50%

Hunting,collecting etc.

26%

Habitat loss and fragmentation

an example from tropical seagrass beds