Final Bio Exam

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ecological biogeography

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- examines the current relationship between eclogical variables (including climate and ecological interactions) and the composition and diversity of ecological communities

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historical biogeography

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- uses phylogenetic and geological information to make inferences about the history and distribution of life on earth

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difference between biomes and biogeographic regions

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biomes- ecological
biogeographic regions- historical
- biomes are to ecological biogeography as biogeographic regions are to historical biogeography

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biomes

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- regions with similiar climate have similar ecological communites that are characterized as different biomes

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basic structure of ecological communities

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- depends largely on climate
- the structure of ecological communities in different parts of the world is largely determined by differences in climate
- there is no place on earth with very high precipitation and very low temperatures (traingular shape of the graph)

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tropical rainforest

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- high primary productivity
- warm, wet climte
- vertical stratification
- very high species diversity
- epiphytes
- the horn of africa (Somalia, Ethiopia) is NOT covered in tropical rain forest

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temperate decidious forest

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- strongly seasonal climate
- relatively high rainfall

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Tundra

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- permafrost
- high winds, no trees
- low species density
- low rainfall
- similiar plant communities occur both in the high artic as well as at the tops of high mountains around the world
- similiar climate produces similiar ecological communities

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Desert

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- low rainfall (<30 cm)
- hot OR cold
- organisms adapted for water storage
- CAM, C4 photosynthesis
- CAM and C4 photosynthesis differ from the usual C3 photosynthesis in using less water in the process of capturing energy from the sun

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Savannah

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- wet and dry seasons
- fire adapted plant species
- large mamalian herbivores and predators

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similar patterns in community structure

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- observed with increasing latitude and increasing altitude
- the same general patterns found in moving north or south from the equator can also be found on a much smaller spatial scale in moving up the side of a mountain

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Ethiopia

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- mistake in book as horn of africa as tropical rainforest
- Ethiopia for example has a great diversity of ecological communities
- it is not however covered by tropical rain forest
- Raven model not too bad but still rather simplistic, in reality it is more complex

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Natural vegetation in Africa

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- one the left is a more detailed and informative map of of biomes of Africa
- errors found in introductory textbooks result in part form difficulty of nearly categorizing eery spot on earth into one of a few biome categories since there is a great diversity of ecological communities on earth
- in part also due to sloppiness of some text book writers
- composite statellite image in with red corresponds to green plants
- highlands of ethiopia are green but most of somalia is not
- map on the left indicates that most of the Horn of Africa is steppe, (grass, brush and thickets), semi desert
- gradual transition from forest to desert as one moves north from central Africa
- north through increasingly open biomes: woodland savanna, bush-grass savanna, grassland and semi-desert

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biogeographic regions

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- named for their characteristic flora and fauna
- reflect independent evolution of unique flora and fauna in each region due to historical isolation

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communities in biogeographic regions

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- different biogeographic regions with similiar climate have similar ecological communities often composed of very similiar looking organisms that are NOT closely related to their counterparts in other regions
- similar body forms have evolved independently in different biogeographic regions, presumably in response to similiar ecological conditions

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African sunbirds

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- remarkably convergent with the New World Hummingbirds in morphology, behavior, and ecology but the two groups are not closely related to each other

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Biomes vs. bigeographic regions

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- biomes reflect the interaction between organisms and climate (ecology)
- biogeographic regions reflect history

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historical biogeography

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- uses phylogenic and geological info to make inferences about history and distribution of life on earth

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Kinds of evidence used in historical biogeography

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- phylogenies- a "molecular clock" used to estimate dates
- fossil record- including pollen
- current distributions of organisms
- geologic and climate history

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southern beech

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- the distribution of southern beech makes sense in light of what we know about continetal drift
- southern beech and other organisms with similiar distributions evolved millions of years ago when South America and Australia were still connected to each other via Antartica
- they are still found in S. America and Australia but have disappeared from Antartica which has drifted to the south and become colder

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vicariant event

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- the formation of a barrier to dispersal that splits a species distribution
- vicariant events are thought ot be an important driver of speciation in many organisms
- populations split by some geographic barrier may evolve differences through genetic drift and or natural selection to different environments, eventually becoming different enough that they can no longer interbreed

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New Zealand

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- many species in New Zealand have a geographic distribution similar to that shown above
- suggesting that a common vicariant event affected all of them the same way
- historical changes in sea level and the elevation of land masses provide an explaination for this pattern and the distributions of organisms help confirm the geographic hypothesis

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geographic patterns

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- a given vicariant event may split the distribution of many organisms in the same region leading to similiar geographic patterns

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Intraspecific phylogeography

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- molecular genetic data can be used to make inferences about the history of the populations within a species
- phylogenetic trees can be built using individual organisms rather than species as the taxonomic units

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Black mountain corridor

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- Professor Schneider and colleagues
- showing the likely importance of the Black Mountain Corridor as a barrier to dispersal for rain forest critters in NW Austrialia
- this narrow strip of rainforest has dissapeared and reappeared over the course of thousands of years as the climate in this region alternated between relatively wetter and drier conditions
- when the extent of rain forest was reduced, the BMC was a barrier to gene flow between isolated populations of these forest adapted species

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Island biogeography

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- species diversity on islands is a function of immigration and extinction rates which depend respectively on distance and the source pool (mainland) and island size
- the theory of island biogeography first developed by MacArthur and Wilson proposes that
- the species present on the islands is largely a function of change historical events ( the effects of which vary in a predictable way for islands of different size and distance from the mainland) rahter than the differnces in the particular ecological conditions encountered on different islands

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typical patterns of species diversity on islands

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- typical patterns of species diversity on islands
-slide shows data for reptiles and amphibians
-similar patterns are observed in other groups of organisms and in other sets of oceanic islands

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area affect in the MacArthur- Wilson model

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- two islands the same distance from teh mainland should have similiar immigration rates ( the rate at which new species appear on each island)
- this will decline with increasing numbers of species up to the total number of species on the mainland (P)
- the theory supposes that the larger islands will have a lower extinction rate because they support larger populations of each species, such that each is less likely to go extinct
- the number of species on each island is predicted to reach an equilibrium level at the point where immigration and extinction rates are equal- this results in a larger number of species on the larger island

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The distance effect in the MacArthur wilson model

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- Islands closer to the source of colonists (such as a continental land mass) have higher immigration rates than that of more distant islands and as a result have a larger number of species at equilibrium

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data in graphs

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- two graphs show the same data on normal and logarithmic scales respectively

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Small, distant islands

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- have fewer bird species
- islands of about the same size have different numbers depending on how far they are from source of colonists

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experimental test of the theory of island biogeography

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- Dan Simberloff in the florida keys getting ready to warp a small mangrove island before furnigating it to kill all the insects
- magrove islands were wrapped so that insect faunas could be eliminated with pesticides
- then recollization of the islands was followed over the next 2 years

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results

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- the number of species on each island at the end of the experiment was similar to the number at the beginning with island 1 having the most species and island 4 the least
- the species composition of each island was however different before and after the experimental treatment
- in other words, the species that recolonized each island were not necesarily the same speceis that were there prior to the experiment

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Island biogeography is applicable to

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- mountain tops
-coral reefs
- fresh water wetlands
- habitats fragmented by human activities
- species adapted to living in specific environments may be effectively isolated by unsuitable intervening habitat
- for example, mountian tops may be islands in a sea of lowland vegetation from the perspective of organisms adapted to live in montane environments

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Rondonia Brazil

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- two new roads were cut through the forest, allowing access to this region
- 11 years later a substantial number of people had moved into this region, cut additional roads into the forest and started clearing land for farming
- just 6 years more the region is heavy settled
-town has grown and now has some greenery as people plant trees and gardens
- abandoned farm fields are starting to regenerate as new fields are cleared
- as original forest becomes fragmented islands of habitat are created
- the theory of island biogeograpy suggests that these small islands will gradually lose many of their species and will eventually support far fewer species than in the original continous forest

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geographical patterns in biodiversity

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- birds and most other organisms have greater species diversity in the tropics than in temperate regions

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why are there so many species in the tropics

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- tropical ecosystems are more productive
- more stable over geoglogical time?
- lack of annual seasonality allows greater niche specialization- narrower niches- more species
- greater predation- less competition- greater niche overlap
- verticle structure increases spatial heterogentiy
- disturbance? high, low, intermediate- tree falls
-biodiversity begets biodiversity-coevolution
- the evolution of a new species of tree may rsult in the evolution of a new species of consumer, pollinators, and commensals
- but this idea alone is not sufficient because it does not explain how high species diversity gets a start