SC BIOL 301 - Global Ecology (5 pages)

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Global Ecology



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Global Ecology

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Landscape Ecology, Species to area, Island Biogeography, Biodiversity, Effects of Earth’s History


Lecture number:
20
Pages:
5
Type:
Lecture Note
School:
University Of South Carolina-Columbia
Course:
Biol 301 - Ecology and Evolution
Edition:
1
Unformatted text preview:

Biol 301 1nd Edition Lecture 20 Outline of Last Lecture I Primary Productivity II Net Productivity III Movement of Energy IV Hydrologic Cycle V Carbon Cycle Outline of Current Lecture II Landscape Ecology III Species to area IV Island Biogeography V Biodiversity VI Effects of Earth s History Current Lecture Landscape Ecology Landscape ecology the field of study that considers the spatial arrangement of habitats at different scales and examines how they influence individuals populations communities and ecosystems Current habitat heterogeneity is a reflection of recent and historical events caused by natural and human forces Legacy effects a long lasting influence of historical processes on the current ecology of an area Natural forces e g tornadoes hurricanes floods mudslides fires continue to cause habitat heterogeneity Human activity has influenced the intensity frequency and ecological influence of natural forces Species richness often increases from the local to landscape scale because habitat diversity increases along this gradient Local i e alpha diversity the number of species in a relatively small area of homogenous habitat such as a stream Regional i e gamma diversity the number of species in all of the habitats that comprise a large geographic area Beta diversity the number of species that differ in occurrence between two habitats These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Regional species pool the collection of species that occurs within a region serves a source of species of all local sites within a region Species sorting the process of sorting species in the regional pool among localities according to their adaptations and interactions Species to area Species area curve a graphical relationship in which increases in area A are associated with increases in the number of species S Human activities have caused widespread fragmentation of large habitats throughout the world Fragmentation decreases habitat area and increases patch number edge size and isolation Small habitats have small populations which are more likely to go extinct Fragmentation causes an increase in the amount of edge habitat compared to the original unfragmented habitat An increase in edge habitat changes the abiotic conditions e g ground temperatures in a forest and the species composition of a habitat Species that prefer edge habitat increase in abundance when fragmentation occurs Declining populations in habitat patches can be sustained by the dispersal of organisms between patches via habitat corridors Corridors increase gene flow and genetic diversity Corridors can be pieces of preserved habitat or they can be constructed for the specific purpose of allowing species dispersal Stepping stones small intervening habitat patches that dispersing organisms can use to move between large favorable habitats useful for flying organisms that do not need continuous corridors to disperse The quality of habitat between fragments i e matrix habitat helps to determine whether organisms can move between fragments Some habitats in the matrix may contain favorable conditions for dispersal whereas others might be inhospitable Island Biogeography When MacArthur and Wilson found that species richness increases with island area they also observed that islands closer to the mainland appeared to receive more colonizing species To test the hypothesis that species richness is determined by both island area and isolation they measured bird species richness on 25 islands in the South Pacific They found that larger islands contained more species Among islands of similar size near islands contained more bird species than far islands The effects of patch size and isolation are similar across multiple types of habitat Equilibrium theory of island biogeography a theory stating that the number of species on an island reflects a balance between the colonization of new species and the extinction of existing species On an uninhabited island many species from a nearby source habitat e g mainland could potentially colonize the island Assuming the species pool of potential colonizers is a fixed size then the rate of new species colonizing the island declines as a function of how many species have already colonized the island As more species colonize the island more species are subject to possible extinction due to chance and negative interactions e g competition predation parasitism Given that the island continues to experience colonization and extinction of species these opposing forces should result in an equilibrium point of species richness on the island This model only predicts the number of species at equilibrium not the species composition at equilibrium At equilibrium there is a continuous turnover of species resulting in a temporally variable species composition Smaller islands should have higher extinction rates islands nearer to a source habitat should have higher colonization rates Combining the effects of island area and isolation reveals predictions regarding Understanding the effects of island size and shape on populations has helped to design nature reserves Since large areas can support large populations with low extinction rates setting aside a single large area will better protect biodiversity than will several small areas Reserves also need to be close enough to allow dispersal but far enough to reduce dispersal of diseases and parasites The benefits and disadvantages of edge habitat must be considered round areas have less edge to area ratios than rectangular areas Nature reserves are typically a compromise among various options Biodiversity Patterns of diversity exist at the global scales e g total species richness is highest near the tropics and declines toward the poles Latitudinal trends in diversity are pervasive and extend even to the oceans In the Northern Hemisphere species richness of most animal and plant groups increase from north to south Mammal species richness also increases to the west likely due to the habitat heterogeneity of mountains Oceans also have increased species richness at lower latitudes Hypothesis 1 Species are continually created over time and without limit because tropical regions have not experienced glaciation Habitats in these areas have had more time to accumulate species Hypothesis 2 The number of species in an area reflects an equilibrium between the processes of


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