Tolerance range

Generalists vs. Specialists

Who Lives Where, and Why?

Abundance and Distribution of Species

Liebig's law of the minimum:

The single factor closest to these survival limits is the critical limiting factor that determines where a particular organism can live. The major factor is one in the minimum.

or: single environmental factor in shortest supply relative to demand is the critical determinant in species distribution

Shelford added to Liebig's work:

Single environmental factor closest to tolerance limits determines where a particular organism can live

Shelford's principle of tolerance limits:

Each environmental factor has both minimum and maximum levels called Tolerance limits, beyond, which a particular species cannot survive or is unable to reproduce.

For terrestrial organisms: temperature, moisture, and nutrient availability.

For aquatic organisms: salinity, gradient (water current).

Sometimes the requirements and tolerances of species are useful indicators of specific environmental characteristics - environmental indicators (trout, lichens etc.).

Limiting factors include ABIOTIC (physical) factors and BIOTIC factors

Abiotic Factors: Light availability/day length, seasonality; moisture/water availability; temperature, diurnal temperature range; height or depth, pressure; salinity; wind; pH, CO₂, O₂, availability of N, P, K, Ca, etc.

Biotic Factors: Competition; predation; parasitism; disease; pollinators, dispersal agents; food availability; species density /distance to nearest neighbour).

2 basic strategies for surviving

- in a broad range of environmental conditions: " generalists “.

- in a narrow set of environmental conditions: " specialists ”.

All species have a tolerance range within which they can cope with the conditions they experience.

The tolerance range is within the organism, i.e., it is the ability of the organism to withstand extremes of different limiting factors.

Different ecological groups:

Ø Eyrobionts – organisms with large range tolerance to an ecological factor.

Ø Stenobionts – organisms with narrow range tolerance to an ecological factor.

Ø Xerophytes – organisms that are adapted to drought and environmental water shortage.

Ø Homeothermics – organisms with constant temperature not depending on environmental temperature.

Ø Poikilotehermics – organisms with body temperature depending on environmental temperature.

Ø Endemics – species that are localized and may have just one population that inhabits a small area.

Дата добавления: 2014-01-11