Option C: Species and Communities

IB Biology SL Option C Ecology

What is an emergent property of an ecosystem?

Community structure

What affects the distribution of species?

Limiting factors

What can strongly affect community structures?

Keystone species

Why does each species play a unique role within a community?

Because of the unique combination of its spatial habitat and interaction with other species

How can interactions between species be classified?

According to their effect

What happens if two species have identical niches?

They cannot survive in the same habitat indefinitely

Limiting factor

Any biotic (intraspecific or interspecific) or abiotic component of an ecosystem which limits the distribution of a population

Biotic

Living

Abiotic

Non-living

Typical abiotic limiting factors for plants

Light availability (needed for photosynthesis), temperature (too much \= loss of water, too low \= freezing), water availability (needed for photosynthesis + cell tugor), salinity, wind velocity, soil pH, etc.

Salinity

Concentration of salts in water or soil

Typical abiotic limiting factors for an animal

Temperature --\> a narrow temperature range, depending on ability to maintain thermal homeostasis and body size (SA:V ratio)

Territory --\> affects capacity to mate, avoid predators, forage, etc.

Food availability --\> influences population size and distribution, depends on each species' diet, may limit their territory

Poikilotherms

Organisms that cannot regulate/maintain thermal homeostasis, must occupy environments according to temperature needs (e.g. reptiles, fish)

Homeotherms

Organisms that can regulate/maintain thermal homeostasis, can occupy a wider range of habitats

Intraspecific

Within a species

Interspecific

Between species

Shelford's Law of Tolerance

States that population have optimal survival conditions between the critical minimal and maximal thresholds of limiting factors (bell shaped curve).

The optimal zone

Central portion of curve, the optimal range of an environmental factor (conditions favor maximal reproductive success and survivability)

Zones of stress

Between the optimal range and high or low limit of tolerance, organisms can survive but with reduced reproductive success

Zones of intolerance

Outermost regions of the curve (the extremes), organisms cannot survive

Who proposed The Law of Tolerance in 1911?

Victors Ernest Shelford, an American zoologist

A: Distribution of one animal and one plant species to illustrate limits to tolerance and zones of stress --\> Plant example

Plant growth is affected by salinity levels in the soil

Glycophytes

Plants that are NOT salt tolerant --\> easily damaged by high salinity
Most plants are glycophytes

Halophytes

Plants that ARE salt tolerant --\> may be stressed in freshwater
Less than 2% of all plants are halophytes

How does cultivation of land for agriculture (e.g. irrigation, grazing) affect salinity levels

Causes the water table to rise and thus concentrates salt at plants' roots
Makes it harder for glycophytes to extract water, may be toxic to them
Must understand salt tolerance for farming

A: Distribution of one animal and one plant species to illustrate limits to tolerance and zones of stress --\> Animal example

Coral species form connected reefs which are impacted by changes in the ocean's temperature

What does coral polyps receieve nutrition from?

Photosynthetic Zooxanthellae (an algae) that lives in the polyp's endodermis

Endodermis

The innermost layer of the cortex in plant roots

The Zooxanthellae cannot survive in ocean temperatures lower than

18 degrees Celsius

The Zooxanthellae cannot survive in ocean temperatures above

35 degrees Celsius

What happens to the coral reef if temperature extremes kill the Zooxanthellae or cause it to leave?

The coral begins to bleach

What is the typical optimal growth range fro reef-building coral species in waters?

Between 20 and 30 degrees Celsius (meaning tropical and sub-tropical regions of the world)