Today –finish biodiversity (Chapter 23) –start conservation biology (Chapter 25) Wednesday...
-
Upload
laurel-crawford -
Category
Documents
-
view
220 -
download
4
Transcript of Today –finish biodiversity (Chapter 23) –start conservation biology (Chapter 25) Wednesday...
Today– finish biodiversity (Chapter 23)– start conservation biology (Chapter 25)
Wednesday– conservation biology
Friday– quiz!– conservation biology
Monday– historical biogeography (Chapter 24)
Wednesday– ecosystem management (outside reading)
Conservation Biology - a mission-oriented science that focuses on protecting and restoring biodiversity
Biodiversity
1. All forms of life
2. All levels of organization (subpopulation to biosphere)
3. All interactions among forms of life and the environment
Where is the biodiversity?
• Endemic species – restricted to a small region– isolated areas (islands, mountain ranges)– product of unique habitat, climate features
Biodiversity hotspots - areas with a high concentration of endemic species, experiencing rapid habitat loss
• Hotspots:– 1.4% of the land area– 44% of vascular plant species– 35% of terrestrial vertebrate species
• But…– 20% of the human population, which is…– growing at 1.8% per year (vs. 1.3%
worldwide)– each hotspot has already lost 70% of its
vegetation
Current Status of Biodiversity• 1.4 million described species, possibly
10 million in total
• Background extinction rate – rate of species loss in the absence of human activities– fossil record: species survive 1-10 million
years– one year: one species has a 1 in 1-10
million chance of going extinct– total: 1 extinction per year
• Mass extinction – loss of large number of species– usually due to catastrophic volcano or
meteor impact– very rare (5 times in 3 billion years)
• Current rate of extinction???
• Some estimates for current rate:– 1 species per hour– 1 million species total, so far– 10% of all species so far– 8.8% of all species– 27,000 species per year– 20% of neotropical plant species– 100 to 10,000 times the background rate
• Numbers of threatened/endagered species:– 5,188 vertebrates (9%)– 1,992 invertebrates (0.17%)– 8,321 plants (2.89%)– 2 lichens (0.02%)
• Since 1600, ~1000 species have gone extinct (probably many more)
Why do species go extinct?
2 separate processes:
1. Something causes a large population to decline.
2. Small populations go extinct.
Causes of species declines
1. Habitat destruction and fragmentation
2. Introduced species
3. Exploitation and overharvesting
4. Pollution
5. Climate change
USA
1. Habitat destruction and fragmentation
Fragmentation – disruption of extensive habitats into small, isolated patches
Relaxation – loss of species from isolated habitats over time
Area
S
• Edge effects – negative impacts adjacent to habitat boundaries
• Forest edges:– more sunlight– drying– high winds– tree mortality– invasive species– more predators
Core area
Edge area
• Core area – part of a patch not impacted by edge effects
• Patch size is not always the best predictor of patch quality
2. Introduced species
• Humans are constantly moving species between continents, islands
– deliberate or accidental
• Most serious impacts on islands– low species diversity– few native predators– animals lack anti-predator defenses,
resistance to diseases
• Characteristics of invasive species– pioneer species– high dispersal rates– found in disturbed habitats, but…– some can invade undisturbed communities
• Why are invasives successful?– no diseases, herbivores, parasites,
predators– better competitors than native species
• Introduced diseases – exploit lack of evolved resistance– Dutch elm disease – American elm– Chestnut blight – American chestnut– avian malaria – Hawaiian birds– Rinderpest – African ungulates– chytrid fungus – amphibians
Net result of invasive species– homogenize ecological communities
around the world– drive native, endemic species extinct
3. Exploitation and overharvest
• Direct exploitation for food– overfishing– “bycatch” in fisheries – killing non-target
species (birds, marine mammals)– “bush meat” – harvest of wild animals for
food• can be sustainable, but often not• threatens many large mammals, primates
• Global trade in wildlife– birds, orchids, cactus, primates – captured for gardens, pets, zoos, etc.
• Many species driven extinct before hunting/harvest regulations were in place– passenger pigeon, island tortoises, marine
mammals
Exam
• Definitions, compare-contrast – 5 points each (20 points per page)
• 5 questions – 12 points per question
• bonuses – 3 points each
• dropped the question with the lowest score
• Average grade = 86
Causes of species declines
1. Habitat destruction and fragmentation
2. Introduced species
3. Exploitation and overharvesting
4. Pollution
5. Climate change
4. Pollution
• Most important for aquatic systems– chemical pollutants– acid precipitation
• Bioaccumulation – process by which toxin concentrations increase in living tissues
– concentrations increase through the food chain
5. Climate change
Why do small populations go extinct?
• Demographic stochasticity – chance events that occur at small populations size– failure to breed or survive– failure to find a mate– skewed sex ratio
Dusky Seaside Sparrow
• Environmental effects – unpredictable events that reduce survival or reproduction– droughts, floods, fires, storms
• Genetic effects at small population size– inbreeding– genetic drift– random mutations
• Extinction vortex – combination of genetic, environmental and demographic factors that drive a small population to extinction
Heath hen
• 1700 – throughout the northeast coast
• 1907 – 50 left on Martha’s Vineyard
• 1915 – 2000 birds
• 1916 – fire
• 1917 – goshawk invasion
• 1920’s – poultry disease
• 1927 – 13 birds, mostly males
• March 11, 1932 – last known sighting
• Minimum viable population – smallest population has a specified probability of surviving for a certain time– usually 95% chance of surviving for 100
years
• How big?– at least 50 individuals to avoid
demographic stochasticity– at least 500 individuals to avoid genetic
effects– realistically > 1000 but varies by species
Reasons for protecting biodiversity
1. Intrinsic – valuable for its own sake
2. Instrumental – beneficial to humans
Instrumental Reasons for Protecting Biodiversity
1. Economic benefits– food– drugs– cultivated crops– ecotourism
2. Ecosystem services – quantifiable services that an ecosystem provides to humans
– often very valuable economically
Examples:– moderating climates– mitigating floods and droughts– eliminating waste and toxins– pest control– pollination
Pollinators
• Insects pollinate 2/3 of crop species– ~25% of foods consumed
• U.S.: $20 to 40 billion in agriculture
• Evidence that many pollinators are declining– bats– honeybees
hummingbirds
3. Maintenance of ecosystem function
• How many species can you safely remove?
• How do you ensure maximum productivity in managed or natural ecosystems?
More diverse ecosystems are more stable
Diversity-productivity relationship
• How are plant species richness and primary productivity related?
• 3 possibilities:
Why would productivity increase with richness?
• Greater odds of encountering a super-productive species
• Complementarity – use of different resources by different species