Biogeographical & ecological processes, lecture 33 Flashcards
Problems with biomes
classification
- can’t map a continuum which is what they are
- in reality there aren’t clear lines between vegetation types
- therefore, biomes don’t exist they are artificial classes along a spectrum
Problems with biomes
classifying vegetation
- there are lots of different properties of vegetation
- eg: canopy structure: height, cover, leaf structure
- eg: microclimate: temp. and humidity
- eg: species composition: density, frequency, richness
Problems with biomes
distribution of vegetation
- at smaller regional/local scales, other factors control the distribution of vegetation such as, soil/rock variations, topography etc.
Problems with biomes
impact of humans on natural biomes
humans have disturbed all natural biomes, mostly to a severe extent
Why are biomes useful?
- help to display/explain the global distribution of vegetation
- helps explain relationships between plant communities. climate and other factors (can expand on this)
Communities
2 definitions
- An assemblage of two or more species populations living together
OR
- An interrelated group of species populations with a functional identity
What do communities possess which individual populations don’t?
multiple emergent properties
Example of an emergent property
spatial relationship
Who has the communities concept been debated between?
Clements and Gleason
What is current research interested in, relation to communities?
- complex interrelationships within and between plants
- which communities are instable/vulnerable
Ecological variables (4 interacting groups of factors)
- Abiotic/physical
- Biotic (ex. human)
- Anthropogenic
- Historical or evolutionary
Distribution of a species population is a function of
2 factors
- resource requirements
- ability to exploit available resources
Abiotic factors
Non-living aspects of the environment, chemical and physical
Which 2 main abiotic factors do plants respond to?
climate and soil
Abiotic factors
(important climatic parameters)
5
- Mean annual temp.
- Amount of temp. fluctuation
- Annual rainfall
- Degree and timing of fluctuation in rainfall
- Potential evapotranspiration
Abiotic factors
(important soil parameters)
5
- Depth
- Nutrient availability
- pH,
- Water retention & drainage
- Soil structure
Abiotic factors
For every physical parameter, there are min and max levels beyond which…
organisms metabolism can’t be sustained
Optimum level of an abiotic factor
A level at which growth and reproduction are maximised
Response of one species to an abiotic factor
- similar response over whole species
- but individuals of some species can vary in response to an abiotic factor - different tolerance range
Tolerance range of plants to an abiotic factor varies with…
how?
age,
younger plants have lower tolerance
Liebig’s law of the minimum
The most limiting factor controls the response of an individual
Problems with Liebig’s law of the minimum
2
- Implies that changes in factors other than limiting factor have no affect on plant growth
- Implies that if we remove effects of one limiting factor another will come into operation
The presence or absence of a species for a given location depends on whether any individual of the species is …
able to tolerate the set of abiotic conditions at that point
Where do more individuals survive at - the extreme optimum conditions or around the average?
around the average
Species distribution reflect…
environmental gradients
