The status of biodiversity Marleen De Troch Ghent

The status of biodiversity Marleen De Troch Ghent University Marine Biology Section Krijgslaan 281/S 8 Tel. 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 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 (2) 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 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 km 2 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, (3) time for evolutionary divergence) (4) (3) special adaptations required to live under high pressure, (5) chemically reducing and metal-rich environment (6) (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