how many species are there, globally? range of estimates: 2 – 100 million best estimate: 10...
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How many species are there, globally?
Range of estimates: 2 – 100 millionBest estimate: 10 million1.4 – 2 million species have a name.
An estimated 97% of all species are invertebrates, and within these, insects are by far the most numerous (an estimated 1-30 million species).
In one study of just 19 trees in Panama, 1200 species of beetle were discovered , of which 80% were previously unknown to science.
Within the vertebrates species: 23,500 ray-finned fish, 9000-10,000 birds, 7,984 reptiles, 5400 amphibians, 4475-5000 mammals.
70% of the world's species occur in only 12 countries: Australia, Brazil, China, Columbia, Ecuador, India, Indonesia, Madagascar, Mexico, Peru, and Zaire.
On average, 3 new species of birds are found each year
An estimated 40 percent of freshwater fishes in South America have not yet been classified.
The deep sea floor may contain as many as a million undescribed species.
Hydrothermal vent communities, discovered less than two decades ago, >20 new families or subfamilies, 50 new genera, and 100 new species were found.
How to measure species diversity?
Counting the number of species has several challenges:
• species recognition (especially the small ones)• the influence of sampling effort and sample size
1 transect: 3 species
2 transects: 5 species
3 transects: 8 species
4 transects: 8 species
5 transects: 8 species
Number of individuals in sample
Nu
mb
er
of s
pe
cie
s in
sam
ple
The sampling artifact:A bigger sample usually contains more species.
Community 1
Community 2
The sampling artifact:Can be avoided by using diversity indices, rather than species numbers.
Number of individuals in sample
community 2
Fisher’s does not change with sample size.
community 1
Fis
her’s
How do you figure out how species numbers increase with area?
Nested sampling design:
Total species number in an area: 403 species.
403
Nested sampling design:
Average species number of 305.
341
280
312
4patches
288
How do you figure out of species numbers increase with area?
Nested sampling design:
Average species number of 266.
220
305289245
269301
242
8patches
256
How do you figure out of species numbers increase with area?
Nested sampling design:
Average species number of 188.
150
213
187
145
191
228
202
40patches
How do you figure out of species numbers increase with area?
Nested sampling design:
Average species number of 160.
321
55
105
154
225
188
150
150patches
193
96
113
0
50
100
150
200
250
300
350
400
450
0 200 400 600 800 1000 1200
Area size (ha)
Spe
cies
Num
ber
4
4.5
5
5.5
6
6.5
0 1 2 3 4 5 6 7 8Log Area
Log
Spe
cies
Num
ber
cAzS logloglog
The increase in the log of species number is proportional to the increase in log area.
zcAS
4
4.5
5
5.5
6
6.5
0 1 2 3 4 5 6 7 8Log Area
Log
Spe
cies
Num
ber
Examples:
From Rosenzweig 1995
• z-values are quite similar between taxa, continents, ecosystems.
• z-values are often in the range: 0.1-0.2.
• c-values vary, expressing systematic differences in biodiversity between taxa, ecosystems, etc.
Generalized species-area curve for nested samples within continents:
cAzS logloglog
Log area
Log
sp
eci
es
nu
mb
er
Productivity gradient:
More productive ecosystems usually have more species per area. But, highly productive ecosystems often have reduced diversity.
Spatial patterns of biodiversity:
Latitudinal gradient:
Biodiversity decreases between the species-rich equatorial tropics and the species-poor polar regions.
Habitat heterogeneity gradient:
More spatially variable environments have more species per area.
Island patterns:
Islands have fewer species per area than their associated mainlands.The further away the island, the fewer species.
Productivity gradient.
Productivity
From Rosenzweig 1995
Cold & dry
Moist & warm
Habitat heterogeneity gradient.
Number of plants per 300 m2 plot beside the Hood River, Canada.
From Rownsend, Begon and Harper 2003
Habitat heterogeneity gradient.
Bird diversity in two continents
From Rosenzweig 1995
Latitudinal gradient:
From Rosenzweig 1995
Islands have fewer species than equal areas on the adjacent mainland.
Species-area curves for islands are different:
mainlandislands
403
305
266
Islands have fewer species than equal areas on the adjacent mainland.
Species-area curves for islands are different:
188160
55
42
141
180
From Rosenzweig 1995
Islands:
Mainland:
New Guinea:
New Guinea islands:
From Rosenzweig 1995
mainlandislands
403
188160
266
305
42
141
180
19
110
166
Island further from the mainland have fewer species than islands of equal size closer to the mainland.
Species-area curves for islands are different:
• z-values for islands are usually greater than for mainlands. Generally, z = 0.2 – 0.6.
• z-values are greater with the farther they are from the mainland.
Generalized species-area curve for islands and their associated mainlands:
cSzS logloglog mainland
Log area
Log
sp
eci
es
nu
mb
er
close farislands
Rosenzweig 1997
Interprovincial species-area curve:
• larger continents (provinces) also have more species and the z-value for interprovincial species-area curves is 1 or greater.
The three biological scales of species–area curves.
Rosenzweig M L PNAS 2001;98:5404-5410
Temporal patterns of biodiversity:
In evolutionary time:
Over millions of years diversity stays relatively constant. That means, relatively fast recovery from mass extinction events.
In succession:
Diversity increases in the course of succession.
In the history of life on earth:
Over hundreds of millions of years, diversity increased.
With disturbance frequency:
Intermediate disturbance frequencies have highest diversity.
Succession:
Disturbance frequency:
Disturbance
From Rosenzweig 1995
Algae and barnacles on rocks of different sizes
From Rosenzweig 1995
Disturbance frequency:
Evolutionary time:
Evolutionary time:
From Rosenzweig 1995
Uintatherium
Hyracotherium
From Rosenzweig 1995
From Rosenzweig 1995
In the history of life on earth:
Pre-cambrian
Cambrian
Devonian
Ordovician
Triassic
Townsend, Begon and Harper 2003
Other patterns:
Food web gradient:
Higher trophic levels usually have lower diversity than lower trophic levels. Exception: there are more animal than plant species. There are more
parasite than host species.
Body size:
Within a taxon, there are more intermediate-size species than either very large or very small species.
Food web gradients:
From Rosenzweig 1995
Patterns with body size
From Rosenzweig 1995
Dragonflies and Damselflies
Patterns with body size
From Rosenzweig 1995
Patterns with body size
From Rosenzweig 1995
Patterns in space
Log areaLog
spe
cies
num
ber
productivity
# sp
ecie
s
Habitat variety
# sp
ecie
s
Latitude
# sp
ecie
s
mainland
Log area
Log
spe
cies
num
ber
close farislands
Time during successionSpe
cie
s nu
mbe
r
Disturbance frequencySpe
cie
s nu
mbe
r
Millions of years
Spe
cie
s nu
mbe
r
Patterns in time
Hundreds of Millions of years
Spe
cie
s nu
mbe
r
Trophic level
# sp
ecie
s
Two more patterns
Body size within taxon
# sp
ecie
s
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