Biogeography Final Exam

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8. Biotic Interactions (Competition)

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Competition occurs when organisms living in the same habitat are demanding on the same environmental resources.

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Gause principle

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Principle of competitive exclusion. States that in a stable ecosystems populations of two or more species cannot occupy the same niche.

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Plants compete for different resources such as:

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Sunlight –plants compete for sunlight through shading e.g. in forests taller plants win the competition over the short plants.
– Nutrients and water –root competition.
– Allelopathy –this is a kind of chemical warfare in plants.

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There are two approaches for studying plant ecology:

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(1). Autecology
(2). Synecology

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(1). Autecology

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– This is the study of the requirements and tolerance of individual organisms or species.
– A species range of tolerance to an environmental factor takes the form of a bell- shaped curve.

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(2). Synecology

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– This is the study of species abundance and competitive relationship in relation to other species in a community.
– The abundance of a species in a community can be expressed by a bell shaped curve.

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Physiological optimum (auteocology)

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The environmental condition under which a species grows most vigorously in a laboratory (without competition).

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Ecological optimum (synecology)

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The environmental condition under which the species occurs most abundantly.

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Potential vs. Actual Range

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Under natural conditions the potential range of a species is usually much larger compared with the actual (realized) range

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Biome

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- a large geographic area with similar or unique plants, animals, and climate.
- Biomes are classified according to the predominant vegetation and characterized by adaptations of organisms to that particular environment

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1. Tropical Rainforest Biome (TMF)

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evergreen forests that have the following characteristics.
– Hygrophylous
– Trees at least 30 m tall
– Rich in thick-stemmed lianas as well as woody and herbaceous epiphytes

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Lianas

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Various long-stemmed, usually woody vines that are rooted in the soil at ground level and use trees, as well as other means of vertical support, to climb up to the canopy in order to get access to well-lit areas of the forest.

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Myers definition of TMF

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- Evergreen or partly evergreen forest
- no less than 100 mm of precipitation per month
- mean annual temperature of more than 24°C
- frost free

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Distribution of TMF

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– South America 56%
– Southeast Asia 26%
– Africa 18%

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Ecological Characteristics of TMF

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• The most species-rich ecosystem is the world –high biodiversity.
• Covers 6-7% of the globe but accounts for 50-80% of all species. The species diversity of the greatest magnitude occurs among insects.

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Structure and Stratification of the TMF

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A stratum - discontinuous emergent layer
B stratum - continuous canopy layer, dominant trees
C stratum - sub-dominant and immature trees
D stratum - smaller trees, palms and ferns
E stratum - herbaceous plants and seedlings

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Jangle in the TMF

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Disturbance creates light patches that promote a tangled mass of dense vegetation.

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Characteristics of TMF trees

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- Straight trunks with thin barks and shallow roots.
- No growth rings (grow continuously)
- Large, thick sturdy leaves. Drip leaves
- Typically have leaves that are not lobed
- Entomophilous(insect pollinated)

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Cauliflory

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botanical term referring to plants which flower and fruit from their main stems or woody trunks (e.g. figs) rather than from new growth and shoots.

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Animal life in the TMF

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In the tropical rain forests animals are either arboreal (leave on canopy) or avian (flying). Also strong detritus life underground.

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Three paradigms developed to explain high biodiversity in the TMF

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1. Time stability
2. Pleistocene aridity and refugia hypothesis
3. Ice- age cooling

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Time Stability Hypothesis

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This hypothesis advances the view that the TMF’s rich biodiversity is a product of its long climate stability.
• However, increasing evidence shows that the tropics have not been stable during geologic time scales.

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Pleistocene aridity and refugia hypothesis

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Proposes that the tropics were arid during the Pleistocene which led to the break up and separation of parts of the TRF which later rejoiced. This phenomena may have repeated a couple of times. Due to repeated separation and rejoining,
allopatric speciation occurred due to geographical
isolation resulting in the high biodiversity.

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Ice- age cooling Hypothesis

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Proposes that during the ice-ages the TRF was invaded by temperate species that migrated to the tropical areas for refuge, which resulted in lots of mingling with tropical alpine and warmth loving vegetation.

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2. Temperate Deciduous Forest Biome

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- This biome is virtually absent in the southern hemisphere.
• July temperatures 21-27°C, January temperatures -6 to 18°C
• Precipitation 800-1200 mm.
• At least 4 months with daily temperature >10°C

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Trees in the TDF

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• The northern limit is where the summers are too cool and short—favors conifers.
• The southern limit is where there are warm winters and no frost—favors tropical species.

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Arcto-Tertiary Geoflora

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The deciduous forests that we see in North America today are a remnant of a previously more widespread composition.

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Explanation of subsequent shrinking of the once widespread vegetation of the early Tertiary period

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(1) Uplift of the Rocky mountains and the subsequent rain shadow.
(2) Aridification of the central plains due to rain shadow effects following the formation
of the Rockies.
(3) Glacial cooling up north –this led to the expansion of Tundra up north and the polar region which led to the shrinking.

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2 Types of Soil found in TDF

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1. Alfisols (grey-brown podzolic soil)
• More acidic, more organic matter, more fertile.
2. Ultisols (red-yellow pozolic soil)
• Less productive, low organic matter, more reddish.
•More typical of the southern latitudes of the deciduous forests

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Biogeography of Boreal Forests

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impoverished in terms of species diversity (only 8 genera account for most tress).
4 conifer genera and 4 hardwood genera.

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2 Treeless Biomes

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Tundra and Grasslands

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Where is the Tundra biome predominantly found and why?

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In the northern hemisphere because ice is found in the southern hemisphere where tundra would be.

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Why are there no trees in the tundra?

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1. Inadequate heat to support growth = shortness as adaptation.
2. Air warmest near ground, so trees cannot grow as temp increases with height.
3. snow provides shelter during winter = insulator from wind and dessication.
4. Wind speed is lowest near the ground = reduced evapotranspiration and reduced wind damage.

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Where is the Tundra biome located in North America?

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Anywhere above the Arctic Tree-line.

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3 Important shrubs that occur close to the Arctic Tree-line.

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1. Alder
2. Dwarf Birch
3. Sage

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Two groups of the Tundra Biome:

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1. High Arctic Tundra
2. Low Arctic Tundra

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High Arctic Tundra

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So cold that even shrubs cannot grow. EF Koppen Climate = warmest season (July) mean temp is less than 0ºC. No growing season.

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Low Arctic Tundra

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Becomes warm enough that shrubs can grow. ET Koppen Climate = warmest season (July) mean temp is 0-10ºC.

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Permafrost

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Implies the permanent freezing of subsoil, however active layers seasonally thaw. Because meltwater cannot sink below the permanently frozen layer, soil is constantly saturated.

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Thermokarst Lakes

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Rounded lakes formed due to differential thawing of active layers of permafrost in the summer/warm season. Becoming more common due to anthropogenic influences.

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Main soil formation process of tundras:

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Solifluction if Soil Fluction

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Soil Fluction

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A type of mass wasting characterized by water - logged sediment slowly moving down slope along impermeable material.

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Temperate Grassland Biome

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Biome that exhibits an absence of trees and is composed of physiogenomic vegetation units that are dominated by grasses (Gramineae).

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Grasses of Grasslands

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- most are perennial (return yearly), with less than 5% annuals.
- grasses mixed w/ Forbes.

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Difference between grasslands and meadows?

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Meadows have the ability to sustain tree growth and are found in wet climates. Grassland climates due not experience enough precipitation to experience or sustain tree growth, and are therefor climatically controlled by their dryness.

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Name for Grasslands in North America?

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Prairie

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Name for Grasslands in Eurasia?

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Steppe

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Name for Grasslands in South America?

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Pampa

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Name for Grasslands in Africa?

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Veld

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Name for Grasslands in tropical Africa?

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Savanna