3-Ecology Biotic factors

What are the biotic factors ?

1. Abundance (numbers, density, biomass)

2. Spatial distribution (dominance, sociability, home range, territory)

3. Natality

4. Mortality

5. Biotic potential (species capacity)

6. Age structure

7. Population dynamics

8. Interactions (intraspecific and interspecific)

General abundance

average number of organisms at the unit of space

Ecological abundance

real number at the specific used space

Calculation of abundance

Absolute :

• not feasible in practice

• total count

• count at test plots

Relative :

• good to show trend

  Index of abundance (0 to 5) :

  • by eye

  • by capturing success

  • by sightings (at specific site and time)

  • by tracks (transect)

  Statistic analyses

Mark – recapture

Lincoln - Peterson index

Spatial distribution

dominance, sociability, home range

Dominance

• as percentage compared to other species represented

• dominant species, codominant, accompaning species

It depends on strategy of feeding, mating, care for offspring and socialization.

Sociability

distribution of the same species members. It depends on strategy of feeding, mating, care for offspring and socialization.

Home range

• space in which one individual satisfies all life needs

• size depends on species, season, time of the day…

Territoriality

• when individul or a group actively defends its home range

• prevents growth of population above habitat capacity

Migration

• periodic :

  • summer/winter

  • day/night

• non periodic

  • emigrations

  • imigrations

    Both are due to changes in habitat (climate, food, abundance)

Natality

• number of “new” individuals in the population in the unit of time

• birth - hatching - division

• positive factor of population growth (normally equivalent to mortality)

Two types of natality and their description

• Maximal natality :

  • biological capacity

  • may occur only short term or in experiment

• Ecological natality :

  • realised, limited by ecological conditions

Fecundity

• women: 400 in lifetime - internal fertilization

• oyster: 60 000 000 in season - external fertilization

• termite (queen): 100 000 000 in lifetime - internal fertilization (only one is fertile)

• tapeworm Taenia sp.: 14 000 per day - internal fertilization (life cycle)

Fertility

possible number of descendants - elephant 5 to 6 in lifetime

Mortality

• number of dead (death rate) in population in the unit of time

• negative factor of poplation growth (normally equivalent to natality)

Types of mortality and their description

• Physiological mortality - minimal, in optimal conditions, theoreticaly

• Ecological mortality - realised, determined by external factors

Survival rate

length of life, how many survive from period to period

Mortality over life phases

Biotic potential of the species

Age structure

Population dynamic (important graph)

Factors causing population fluctuactions

PHYSICAL (independent of density) :

• temperature (ice - fire), moisture (drought-flood), climate

• dominate in more simple ecosystems - tundra, monocultures

• fluctuations are stronger and with lasting consequences

BIOLOGICAL (density dependent) :

• influence is directly proportionally growing

• FEED BACK REACTION (organisms can modify their environment and these modifications can feed back to the organism, generating emergent properties with evolutionary consequences - ex with the prey and the predator, preys are eaten by the ptredators so less preys what leads to less predators)

• dominate in more diverse ecosystems - tropical rain forest

Selfregulation - tendency of all populations

Hyperpopulation - not in interest of any population

What are the types of interactions and their description ?

• INTRASPECIFIC competition : growth of population of one species pushes it toward marginal habitat

• INTERSPECIFIC competition : growth of population of competing species  pushes it into the optimal zone of available habitat

Interspecific interactions and effects on other species 0, +, -