Abundance and Distribution of Species

Generalists vs. Specialists

2 basic strategies for surviving

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

LIMITING FACTORS

• The geographical range of a species is not always limited by the presence of barriers that prevent its spread.

• It is often limited by a particular factor in the environment that limits it ability to survive, grow or reproduce – These are Limiting Factors

Limiting factors include ABIOTIC (physical) factors and BIOTIC factors

Abiotic Factors

• Temperature, Pressure, Wind,

• Moisture, Salinity

• Light availability /day length

• pH, C02, O2, availability of N, P, K, Ca.

Biotic Factors

• Competition, Predation

• Diseases, Parasitism

• Food availability, Pollinators

• Species density

Tolerance Limits

Each environmental factor (temperature, humidity, food supply, etc.) has both minimum and maximum levels beyond which a species cannot survive or is unable to reproduce: lower & upper limits of tolerance.

Tolerance range is the range between these 2 limits.

Abundance and Distribution of Species

• Liebig ’s Law of Minimum:

the environmental factor in the shortest supply is the critical one in species distribution.

Shelford added to Liebig's work:

single environmental factor closest to tolerance limits determines where a particular species

Cactus: 1) dry environment

2) critical factor = T (not freezing

Дата добавления: 2015-09-01