Eco topic 15
human activities cause wide spread
Habitat loss and habitat fragmentation
humans have instigated the __ mass extinction
6th
what activities cause extinction
human activities like deforestation, pollution, fragmentation
to understand the crisis we're in we need to
understand what shapes biodiversity
what are the two key patterns in human extinction and biodiversity patterns
Habitat loss and Fragmentation
what is fragmentation
when a large, continuous habitat gets broken up into many smaller, isolated patches, because of human activities like roads, farms, cities, and development.
how does fragmentation affect biodiversity
changes how species are distributed and how ecological communities function.
what are the two main ways that fragmentation affects biodiversity
#1 Smaller habitats=fewer species because less space, fewer resources and smaller populations are more vulnerable to extinction. #2 More isolation therefore species can't easily move between patches. leads to less gene flow, less immigration and more inbreeding.
what is habitat loss
when a natural habitat is completely removed or destroyed, so it can no longer support the species that live there
how does habitat loss affect species diversity
#1 fewer habitat = fewer species can survive. Species disappear because the environment cannot support them anymore. Less space, food and shelter. #2 Smaller pop. size = higher extinction risk because of interbreeding, more genetic problems and higher chances of being wiped out by random event. #3 Ecosystem functions break down and becomes less stable. less polinators, fwer preds, nutrient cycle changes
what are area effects
how the size of a habitat patch (its area) influences the number of species it can support.
Why are Islands Ideal for Studying Area Effects
#1 They're isolated and therefore reduce migration and species mixing. And this means that species numbers depend strongly on area and extinction rates. #2 sizes vary, so ecologists can test the effects of size. #3 fewer confounding variables. #4 clear boundaries that are measurable, this makes it easy to compare area to the number of species
example of area effects
galapagos islands = small and very far away (high isolation) and PEI = big and close (low isolation)
what is the theory of island biogeography
the theory explains how many species an island can support based on immigration (colonization) and extinction rates. it shows that species reach a dynamic equilibrium
what is a Dynamic equilibrium
when the number of species stays stable because immigration and extinction rates balance each other, even though the actual species present keep changing.
what are the three key ideas of the theory of island biogeography
#1. Island size affects extinction. Larger islands have low extinction rates (more resources, more habitat types and larger populations). #2 Distance from the mainland affects immigration. Islands closer to the mainland get more immigrants than island far away. closer = high colonization rates and more species. #3 Species richness reaches and equilibrium. overtime species stabilizes when immigration = extinction rate.
what does it mean when it says that immigration and exctinction balance eachother out to shape species richness
Species richness is determined by the balance between immigration adding new species and extinction removing species and the point where they equal each other creates a stable number of species.
immigration > extinction → species richness increases
extinction > immigration → species richness decreases
immigration = extinction → species richness becomes stable (equilibrium)
why are extinction rates lower on large islands
Larger islands have bigger populations sizes, so extinction risk is lower, they also have more habitats which allows more species to coexist.
Why do extinction rate increase on larger islands
as the number of species increases, extinction increases due to more competition, more interactions and more chances a species is rare
What determines how many species live on an island
Immigration (it declines with distance from the mainland) and Extinction (negative process, species are lost)
how is species richness on islands determined
by a trade-off between island size (linked to extinction rates) and distance from the mainland (linked to immigration rates)
when more species are present, immigration...
declines because fewer new species are left to colonize
what has the highest biodiversity
large islands that are near the mainland
what has the lowest diversity
small islands that are far from the mainland
S* is what
equilibrium number of species, and comes from the balance between immigration and extinction. the expected level of biodiversity on an island at equilibrium
The slope (z) tends to be steeper on islands and shallower on the mainland, what does this mean?
area has a stronger effect on island species richness
According to island biogeography:
Species richness increases rapidly at first when the area expands, then increases more slowly as the area continues increasing.
The species–area relationship is
non-linear
Can this apply to habitat islands (e.g., forest patches) as well as real islands?
Yes, because habitat patches function just like real islands but instead of being surrounded by water, they’re surrounded by unsuitable habitat.
Species richness increases with island area according to
S=cAz