Bieb 140 Lecture 13

Front 1

Biogeography

Back 1

Study of the geographic distribution of plants and animals. Quantifying patterns of past and present distribution. Understanding the causes of such distributions

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Life Zones, Ecoregions, or Biomes

Back 2

Particular kinds of plants and animals that occur together in particular environment

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Geographic range size distributions

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Majority of species have small geographic ranges. Range changes over time. Due to : speciation/extinction dynamics, ecological effects, historical effects

Front 4

Species geographic range limits factors

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1. Physical barriers

2. Absence of suitable habitats

3. Biotic Interactions

4. Adaptations and gene flow

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Physical Barriers

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Barriers to dispersal

Temperature - some beyond physiological limits

Seasonality

Moisture and precipitation

Salinity

Ocean Currents

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Biotic Interactions

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Competition

Predation

Mutualism

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Endemism

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Occurring nowhere else. Species can be endemic to a location on different spatial scales and taxonomic levels ( to a site, region, family, species)

Front 8

2 Ways to be Endemic

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Originate in a place and never disperse

Range Collapse

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Cosmopolitanism

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Widely distributed throughout the world, not that many species are truly cosmopolitan.

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provinces

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Well defined regions with taxonomically distinctive faunas

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Boundaries

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Between provinces generally sharp. Often coincide with major changes in environment. Some may be results of historical processes

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Wallace's Line

Front 13

Theory of Island Biogeography

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Determined by migration/extinction, source main/far, size small/large

Number of species increases with area and decreases with isolation

Continuous turnover of species

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Three main assumption of Theory of Island

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Biota are in equilibrium\

Immigration and extinction are independent processes

No speciation on islands

Front 15

Diversity at different geographic scales

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Small scale - alpha diversity

Med scale - beta diversity

Large scale - gamma diversity

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Alpha Diversity

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# of species within a sample

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Beta diverstiy

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Species turnover rate between samples. How fast things are changing. Extra species gained by combining multiple samples

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Gamma Diversity

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All species present in a region or in all samples

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relationship between local -regional diversity

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Richness In a sample can never be more than richness in all sample. Bc local richness can never be larger than regionally richness

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Types II Relationship

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Asymptotic, suggests that communities are saturated and local processes are of primary important. Local has carrying capacities. Local processes are small scale ecological interactions such as competition for space and/or resources

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Type I relationship

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Suggest that large scale processes are more important. Large scale processes are mainly historical - speciation, extinction, climate trends

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Macroecology

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Focuses on large scale ecological patterns. To understand processes underlying major biodiversity patterns

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Latitudinal diversity gradient

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Species richness decreases rapidly front he equator to the poles. Common in marine and terrestrial biota.

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Density dependent mortality

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May be an explanation only for plants. Seedling recruitment is negatively density dependent: high species density = lower seedling recruitment of that species. Allows many species to coexist. If density dependent mortality decrease towards high latitude then it can explain LDG for tree species.

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Species Energy Hypothesis

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Species richness of an area is a direct function of available energy. Much more energy for biological activity for low latitudes. Positive relationship between richness and energy for plants and animals.

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Evolutionary explanations of LDG

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Age and climatic stability of the tropic

Changes in rates of speciation and/or extinction with latitudes

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Age and Climate stability of the tropics

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Tropics have been around a long time so diversity may have accumulated over time while always remaining warm and stable. CLimate change usually affects temperate and high latitudes more than tropics.

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Changes in rates of speciation and or extinction with latitudes

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Species in high latitudes adapt to changing climates unlike species in low latitudes.

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LDG - Why we need to understand it

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Tropical diversity is declining due to humans. If we don't understand why tropics are so species rich, then we can't predict the consequences of the declines or formulate management strategies. Relevant for predicting Biotic consequences of climate changes

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Body Size Distribution

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Most species are small but the smallest size the not the most common.

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Shapes of size frequency distributions

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Size ranges are set by functional and or physiological constraints

Distribution of sizes with in the range are controlled by other factors: Energetic MOdel, Fractal dimension of habitat, speciation/extinction rates

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Energetic Model of Body Size

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Body size distributions are set by energetic requirements of species. Smallest individuals are efficient in converting resources into reproductive effort but are limiters by rate of resource acquisition.

Large individuals are better at acquiring resources but can produce fewer offspring.

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Fractal dimension of Habitat

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For large animals - world looks similar. For small animals - world looks complex.

Front 34

Shapes of SFDs dependent on geographic scale

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Entire continent, you see the # of species varying. Locally, no one species sticks out more than the other.

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Why SFDs vary with spatial scale?

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Interspecific competition can lead to flat distribution; competitive exclusion can prevent similar sized species from coexisting. Small species are more specialized so have high spatial turnover, this allows for more small species on continental scales and large species have larger distributions and hence less spatial turnover.

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Implications of Range Size Distributions

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Since most species have small ranges:

Most effort is required to inventory biodiversity

Geographically restricted species are often small so hard to sample

Large bodied species need large ranges, so reduction in range can make them vulnerable to extinction

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Conservation and Management

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Areas with high endemisms targets of conservation. Species area relationships used in reserve design. Macroecological relationships can be used to identify types of species more at risk of extinction. Useful for predicting effects of global climate change.