no member of a species remains alive anywhere in the world
- in practice, not seen for 50 years Ex. Tiny plant on helenurm's island
Referring to the presence on earth
Extinct in the wild
individual species only remain alive in captivity
Define locally extinct
Means no longer found in area it once inhabited
ex. gray wolf of massachusetts
extinct in a county or region but still persists in nan other part of its range (mostly the same as locally extinct)
Define ecologically extinct
persists at such reduced numbers that it's effects on other species in its community are negligible.
Ex. So few tigers that they don't really impact the prey populations So small that they're not worth worrying about
Define extinction rate
predicted eventual loss of species following habitat destruction and fragmentation
My concept paper; smaller areas simply can't support the number of species
What has the overall trend in extinction/ biodiversity been? What are the two kinds of extinction?
99.9% of all known species that ever lived have gone extinct
There has been an overall increase in diversity over time
Natural extinction rates are divided into 2 kinds: background extinction rate and mass extinctions (5; ongoing 6th)
How do we know that 99.9% of species are extinct?
1. Known mostly through the fossil record
2. took place over 3.5 billion years ago
Evidence that there is an increase in diversity over time.
1. As some have gone extinct others have appeared
2. Speciation exceeded extinction
3. But that was over 3.5 billion years.
What is meant by background extinction rate? How does it apply to species with narrow distributions and terrestrial animals? How do we calculate it?
A. Known via fossil record
B. 1 to 10 million years Is the average lifespan before extinction for a species C. Derived from wide ranging marine animals (with fossilize ble hard shells)
a. Good fossil record
1. Always in the same rock layer, lots of individuals
D. May be shorter for species with narrow distributions
a. May not be generalizable for all species!!
1. More vulnerable to habitat extinction
E. Probably applicable to terrestrial mammals
F. Cars example
a. Car lasts 8 years, how of ten will you buy a new one? 1. Every 8 years.
b. What is the extinction rate of cars 1. 1 car / 8 years
2. 1/8 car per year
c. If average life span of a species is 10^7 years, the extinction rate is
1. 1/10^7 species per year (out of 10 million sp, one will go extinct every year.) 2. Expect 1 to 10 species to go extinct per year on average
Possible causes of mass extinctions
a. Climate change
1. Drops in sea level could dry out shallow inland seas
1. 10 km wide
2. 90,000 km/hr
3. Thick cloud of dust, no photosynth, no food
What are mass extinctions?
B. Many species have gone extinct at times with lower extinction rates
C. But diversity has plummeted with these episodes of mass extinction
D. Good news: recoveries occur
a. Overall increase in biodiversity over time
E. Bad news: recoveries require 1-8 million years
Global diversity is at an all-time high. Why do we think this?
Global diversity of species arched all time high in the present geological period
-most advanced groups reached greatest diversity around 30,000 years ago -Insects, vertebrates, plants
-species richness has decreased as human populations have grown
What are examples of current extinctions being caused by human activity?
Elimination of large mammals from Australia, NAm, and SAm, when humans first colonized
-74-86% of megafauna (>100lbs) extinct
-why? Due to hunting and clearing forests
-evidence from paleontology and archeology on all continents
85 species of mammals and 113 species of birds have gone extinct since 1600
2.1 percent of. Mammals
1.3 percent of birds
Trend is increasing
Majority in last 150 years
1/10 years from 1600-1700
1/year from 1850-1950
4/year from 1986-1990
11% of remaining birds and mammals in imminent danger for extinction
What are some ways that humans cause mass extinction?
- meat, skins, plant collectors (orchids??)
- sport (large cats)
- aphrodisiacs (powdered rhino horn)
- hating stuff.
- disease, pest infestations
global climate change
Describe the current extinction rates
Difficult to estimate; 50 year criterion
Currently observed rate for birds and mammals: 0.01% per year
100-1000x greater than background rates
Emphasize birds and mammals because they're big and we have data on them
Estimated from island biogeography: 75 species / day
Assumes 5 million species in topical forest
Based on habitat loss; number of species it can support
Facets of island biogeography: the outline
1. The species-area relationship
2. Equilibrium theory of island biogeography
B. Rate of extinction
C. Rate of colonization
3. Relevance off conservation biology
Possible reasons for species-area relationships of island biogeography. (3)
a. Large islands have a greater variety of local environments and community types
1. Probably true but hard to quantify
b. Large islands allow for greater geographic isolation
1. Increasing likelihood for speciation
c. Large islands have a large number of populations per species
1. Decreasing probability of extinction
Species-area relationship formalized by arhenius (1921)
What's the equation? How do C and Z change?
1. S- number of species on an island
2. A is area of island
3. Z is a constant
4. Power function (curved line); z determines slope of a curve
b. If you graph that on linear scale,it's curved, if you log it, it's a straight line.
c. C and z depend on
1. Types of islands being compared
- A. Tropical vs mainland
- B. Dry vs wet
- C. Any factor affecting diversity
2. Types of species involved
A. Birds vs mollusks
3. C tends to be higher in groups that are high in species number
A. Insects tend to have higher c numbers
4. Z tends to be higher for groups with restricted ranges.
What phenomena does the equilibrium theory of island biogeography seek to explain?
MacArthur and Wilson (1967)
Seeks to explain: increase in biodiversity with area
decrease in biodiversity in more distant islands (from colonist source)
equilibrium number of species (when loss and gains are balanced)
supported by many turnover studies, when extinction if followed by colonization.
What does the rate of extinction depend on in the equilibrium theory of island biogeography?
a. Number of species
1. More potential for extinction with more species
1. Larger area, less extinctions
2. Inverse relationship
A. Larger island has more populations (# of populations)
B. Population size
C. Greater habitat diversity
What does the rate of colonization depend on in the equilibrium theory of island biogeography?
a. Number of species
1. No more colonization if all species are already there.
2. Rate depends on how. Many are there
A. With few species, greater chance that migrant is of a different species
b. Distance from sources of colonists
1. Inverse relationship
A. More colonization of. Close islands
A. easier dispersal from source ( mainland)
Why is the equilibrium theory of island biogeography relevant to conservation?
A. Can be applied to "islands" of habitat
a. Metaphorical island
b. Metaphor works because species usually unable to compete successfully in intervening habitats
B. Predicts loss of biodiversity from habitat loss
a. Small scale
b. When 50% of habitat destroyed, 10% of species eliminated
c. When 90% of habitat is destroyed, 50% of species eliminated
d. When 99% of habitat is destroyed, 75% of species eliminated
1. Based on ultimate extinction including extinction debt
C. Provides guidelines for reserve design