Ecology

Distribution & Occurrence

• Dispersal• Behavior• Biotic– Competition• Resource partitioning/niche differentiation

– facilitation• Abiotic– Tolerance/requirements

Factors Influencing Distribution and Occurrence of organisms

Expansion of cattle egret after arrival to western hemisphere

Limiting Resources

Tolerance Range

• Tolerance range is the range of a physical condition that the organisms can survive in (between the minimum and maximum)– Minimum = smallest amount the organism needs or can cope with– Maximum = largest amount the organism can cope with– Optimum = amount at which the organism does best

• Populations can only become established in areas within the tolerance limit• Hibernation & dormancy are ways of avoiding periods of time where environment is

outside the tolerance limit

Found in this range

• Intolerant (too much)• org. cannot survive

• Intolerant (too little)• required amount not present• org. cannot survive

Environmental gradientlow high

maximumminimum

Tolerance range:application of limiting resource

waterwet dry

too dryTolerance range for “grass”

Limit due to requirement/tolerance

Limit due to tolerance

too wet

Ecological Niche• The totality of an organisms adaptations, its

use of resources, and the lifestyle to which it is fitted– Physical, chemical, biological factors needed to

survive– Behavior– Trophic level– adaptations– Habitat– Abiotic components of the environment

A variety of definitions of “niche” just to show you it is an easy idea that is hard to create a good definition for

• How an organism survives and reproduces in an environment– How it does stuff and what resources it uses

• The place or function of a given organism within its ecosystem. Note : Different organisms may compete for the same niche. – For example, in a forest there may be a niche for an organism that can fly and eat nectar from blossoms.

• niche is the sum of the habitat requirements and behaviors that allow a species to persist and produce offspring– habitat and behavior

• The niche of an organism is its place in the biotic environment, its relations to food and enemies.– Foraging/what it eats

• The environmental conditions and resources that define the requirements of an individual or a species to survive and reproduce

• a niche is a term describing the relational position of a species or population in an ecosystem• the role and position a species has in its environment; how it meets its needs for food and shelter, how it

survives, and how it reproduces. A species' niche includes all of its interactions with the biotic and abiotic factors of its environment.

Competition

• Interaction among organisms that vie for the same resource in an ecosystem

• Intraspecific– Competition between individuals in a population

• Interspecific – Competition between individuals in 2 different

species

Interspecific Competition:competition harms both organisms/species

Competitive Exclusion

• Two species cannot coexist permanently in the same place if they compete for the same resource (at the same time, in the same way)– two species cannot coexist if they have the same

niche• Over time, two competing species can either:

1. coexist, through niche differentiation (or other means)

2. compete until one species becomes locally extinct.

Fundamental (Ecological) v. Realized Niche

• Green Anole (native to FL) and Brown Anole (introduced from Cuba)

Marshes and tree canopies

Ghost of competition past

• The niche differentiation seen in the present is the result of past competition.

• Past competition has resulted in:– Similar species diverging (through selection) so

they do not directly compete (have different niches)

– The extinction of poor competitors whose niches overlapped with the existing organisms (who outcompeted them).

Combined influence on distribution

• The range and distribution of species is due to a combination of tolerance, competitive exclusion, and dispersal ability/opportunity

Tolerance range/limiting factor + Competitiona simple schematic

waterwet dry

Limit due to competition = competitive exclusion

too dryTolerance range for “grass”

Limit due to tolerance

Bush is better competitor in this area; excludes grass

Common Factors Determining Distribution (i.e., where things are found)

Found in this range

• Intolerant (too much)• Predation• Out competed

• Intolerant (too little)• Predation• Out competed

Also dispersal: is the organism or its offspring able to get to an area. If the organism is incapable of reaching an area (or has not yet reached an area) then it won’t be found there.

• Intolerant (too much)• Predation• Out competed•Disease/parasites

• Intolerant (too little)• Predation• Out competed• disease/parasite

barrier to dispersal (no lizards here)

The brownbarnacle competitively excludes the gray barnacle from the lower area even though the gray barnacle could tolerate that area

Tolerance ranges

Area found

Character displacement• Morphological divergence in sympatric populations of similar species • Evidence of niche differentiation that can be seen in present.

More character displacementStickle-back fish in lakes

Community Diversity, Disturbance, & Succession

• Diversity• Community Structure• Organismal Concept & Climax Communities• Individualistic Continuum• Non-equilibrium & intermediate disturbance

hypothesis• Succession

Diversity = richness + relative abundance

Models of community composition

• EQUILIBRIUM=STABILITY=reach and maintain a constant, stable species composition

• ORGANISMAL (interactive) CONCEPT– Species co-exist because they have positive and necessary

interactions

• INDIVIDUALLISTIC CONTINUUM CONCEPT– Associations due to similarity in tolerance and requirements

Intermediate disturbance hypothesis

• Wayne Sousa (1979) studied the effects of disturbance on the diversity of marine algae and invertebrates growing on boulders in the intertidal zone.

• Small boulders high disturbance• Large boulder low disturbance

Succession

• change in species structure of community over time

• one assemblage of species is gradually replaced by another assemblage– Each assemblage=sere

• Facilitation plays a role

Primary succession = bare mineral (new substrate)

Secondary Succession = existing soil and community disturbed

• An example of Secondary Succession by stages:1. A stable deciduous forest community2. A disturbance, such as a wild fire, destroys the forest3. The fire burns the forest to the ground4. The fire leaves behind empty, but not destroyed, soil5. Grasses and other herbaceous plants grow back first6. Small bushes and trees begin to colonize the area7. Fast growing evergreen trees develop to their fullest, while shade-tolerant trees develop in the understory8. The short-lived and shade intolerant evergreen trees die as the larger deciduous trees overtop them. The ecosystem is now back to a similar state to where it began.

Secondary Succession of an abandoned farm field in North Carolina