Lec #3: Factors Limiting Distribution

Factors Limiting Distribution — Biotic Interactions

The local distributions of many organisms are limited by the presence of other organisms (biotic interactions)

(Competition, Predation, Parasites, Disease)

Factors Limiting Distribution — Abiotic Factors Physical and Chemical

Water, oxygen, pH, salinity, nutrients

Light, temperature, soil structure, currents, periodic disturbance (fire)

Competition

(-,-) interaction (one won’t get the resource, and the other uses energy)

Can occur between 2 or more organisms or species that exploit the same types of limited resources and live in the same geographical area

The population level is lower for both species

Intraspecific competition

competition within a species

Interspecific competition

competition between two different species

Interference competition

Direct physical interaction over resources

Exploitative competition

Indirect interaction over

Competitive Release

Natural patterns indicating competition

When species B is absent, species A lives in a wider range of habitats

If competition is strong, the geographic ranges of the two competitors may not overlap but have sharp boundaries

Barnacles: Balanus balanoides (large) and Chthamalus stellatus “thamalus” (small) Example

Competition

Intertidal zone experiment by Joseph Connell (UCSB) - pioneer of experimental marine ecology, British coast

High confidence due to a good control and replication of treatments (any manipulation outside direct removal was controlled)

These barnacles close tightly when tide is low due to filter feeding and preventing water loss (the Chthamalus closes tighter)

Larvae settle in all regions, but adult barnacles have no overlap in distribution (balanus stay in the mean tide and chthamalus stay in the high tide)

Transplant experiment: move Chthamalus low & Balanus high

Results: Balanus dies in upper intertidal due to abiotic factors/desiccation (dries out) because it cannot close tight

Conclusion: Upper limit set by desiccation; Chthamalus can close tighter than Balanus

Balanus grows and displaces the smaller one (it pops off the rock) to reduce competition (more space, more successful)

Removal experiment: marked out quadrats of settling barnacles with replicates and then made maps

Results: Chthamalus survives in lower intertidal when Balanus removed

Conclusion: Lower limit set by competition Balanus grows faster and out-competes Chthamulus for space

Biotic factors with interspecific interference

Predation

(+ , -) interaction

Can limit the distribution of organisms via:

1. direct consumption of prey

2. behavioral modifications of prey in the presence of predators (3 options dependent on location: run farther than others, hide, fight)

Thais (predatory snail Predator) and Balanus (large barnacle Prey) Example

Intertidal predation experiment by Joe Connell

Balanus larvae settle in all regions but Thais adults are found in the low tide and Balanus adults are found in the mean tide

Need a control to make sure the treatment does not stress, kill, or change the behavior

The balanus will be stuck on the rock, but the thais move or need a cage

Cage Experiment:

- Cages exclude Thais and allow Balanus settlement

- Caged control include Thais and allow Balanus settlement

First move the balanus low (cage and no cage)

Results:

1. In cages - Balanus survived (there is no abiotic environ factor limiting distribution)

2. Outside cages (control) - Balanus were consumed

Conclusions:

1. Balanus absolute lower limit is set by Thais which consumes barnacles (predation) — biotic snail predator

2. Thais absolute upper limit is set by Desiccation — abiotic desiccation

Physical and Chemical Abiotic Factors Limiting Distributions

Temperature and availability of water are the two master limiting factors to the distribution of life on earth

- Organisms have upper (45 when protein denatures) and lower (0 freezing point) lethal limits to physical and chemical factors

- Solutions are acclimation or adaptation