Download PowerPoint

How many species are there, globally?
Range of estimates: 2 – 100 million
Best estimate: 10 million
1.4 – 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
The sampling artifact:
Number of species in sample
A bigger sample usually contains more species.
Community 1
Community 2
Number of individuals in sample
The sampling artifact:
Fisher’s a
Can be avoided by using diversity indices, rather than species numbers.
community 1
community 2
Number of individuals in sample
Fisher’s a does not change with sample size.
How do you figure out how species numbers increase with area?
Nested sampling design:
403
Total species number in an area: 403 species.
Nested sampling design:
4
patches
280
288
312
341
Average species number of 305.
How do you figure out of species numbers increase with area?
Nested sampling design:
8
patches
220
269
256
301
245
242
305
Average species number of 266.
289
How do you figure out of species numbers increase with area?
Nested sampling design:
40
patches
150
191
228
145
202
213
187
Average species number of 188.
How do you figure out of species numbers increase with area?
Nested sampling design:
150
patches
321
225
193
188
96
154
105
55
113
Average species number of 160.
150
450
Species Number
400
350
300
250
200
150
100
50
0
0
200
400
600
800
1000
1200
Log Species Number
Area size (ha)
6.5
6
5.5
5
4.5
4
0
1
2
3
4
Log Area
5
6
7
8
Log Species Number
The increase in the log of species number is
proportional to the increase in log area.
6.5
6
5.5
5
4.5
4
0
1
2
3
4
Log Area
5
6
7
log S  z log A  log c
S  cA
z
8
Examples:
From Rosenzweig 1995
Log species number
Generalized species-area curve for nested
samples within continents:
log S  z log A  log c
Log area
• 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.
Spatial patterns of biodiversity:
Productivity gradient:
More productive ecosystems usually have more species per area.
But, highly productive ecosystems often have reduced diversity.
Habitat heterogeneity gradient:
More spatially variable environments have more species per area.
Latitudinal gradient:
Biodiversity decreases between the species-rich equatorial tropics and the
species-poor polar regions.
Island patterns:
Islands have fewer species per area than their associated mainlands.
The further away the island, the fewer species.
Productivity gradient.
Cold & dry
Moist & warm
Productivity
From Rosenzweig 1995
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
Species-area curves for islands are different:
Islands have fewer species than equal areas
on the adjacent mainland.
Species-area curves for islands are different:
Islands have fewer species than equal areas
on the adjacent mainland.
islands
mainland
42
55
160
141
188
266
305
180
403
Mainland:
Islands:
From Rosenzweig 1995
New Guinea:
New Guinea islands:
From Rosenzweig 1995
Species-area curves for islands are different:
Island further from the mainland have fewer species
than islands of equal size closer to the mainland.
islands
mainland
42
110
180
160
188
19
266
305
166
141
403
Log species number
Generalized species-area curve for islands
and their associated mainlands:
log S  z log S  log c
close
far
islands
Log area
• 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.
Interprovincial species-area curve:
• larger continents (provinces) also have more species and the zvalue for interprovincial species-area curves is 1 or greater.
Rosenzweig 1997
The three biological scales of species–area
curves.
Rosenzweig M L PNAS 2001;98:5404-5410
Temporal patterns of biodiversity:
In succession:
Diversity increases in the course of succession.
With disturbance frequency:
Intermediate disturbance frequencies have highest diversity.
In evolutionary time:
Over millions of years diversity stays relatively constant. That means,
relatively fast recovery from mass extinction events.
In the history of life on earth:
Over hundreds of millions of years, diversity increased.
Succession:
Disturbance frequency:
Disturbance
From Rosenzweig 1995
Disturbance frequency:
Algae and barnacles on rocks of different sizes
From Rosenzweig 1995
Evolutionary time:
Evolutionary time:
From Rosenzweig 1995
Uintatherium
Hyracotherium
From Rosenzweig 1995
From Rosenzweig 1995
Triassic
Devonian
Ordovician
Cambrian
Pre-cambrian
In the history of life on earth:
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
Dragonflies and Damselflies
From Rosenzweig 1995
Patterns with body size
From Rosenzweig 1995
Patterns with body size
From Rosenzweig 1995
Log species number
Log area
# species
# species
Latitude
close
far
islands
Log area
# species
Log species number
Patterns in space
productivity
Habitat variety
Species number
Species number
Time during succession
Disturbance frequency
Species number
Species number
Patterns in time
Hundreds of Millions of years
Millions of years
# species
# species
Two more patterns
Trophic level
Body size within taxon