Chapter 3: Ecological and Evolutionary Principles of

Populations and communities

Construction of a Population change Model

dN/dT = f (N,M,R,I,E)

N = population sizeM = mortalityR = reproductionI = immigration (larval settlement)E = emigration

M is a function of physical environment, competition, predation, etc.R function of physical environment, resources (e.g., food)

Marine Populations are dynamic, and change is the rule.

The most important parameters change based on the life history of the organism that you are trying to model.

• For sessile organisms (like barnacles) the most important parameters are: N, I, M

•For mobile populations with large home ranges E, emigration is also important

•For animals that are widely dispersed (deep sea animals): R becomes the most important factor, along with N and M.

Example of Population Model

Barnacles: What parameters matter the most?

dN/dT = f (N, I, M)

I is larval settlement

M a function of larval-adult interactions, overgrowth, predation.Note R doesn't matter if planktonic larvae mainly go elsewhere (are dispersed)

Mortality pattern expected for a species with a planktonic larva. Note higher mortality rate of larval stage.

Planktonic Post-settling stagelarvalstage

Sur

vivo

rs

Survivorship curve

Modes of Population Change

Exponential Growth

Logistic growth Random change

Limiting Resources (Carrying capacity K)

•Space is a limiting resource to these colonies of colonial ascidians

•For marine populations space and food are the most common limiting resources

Metapopulation dynamics

Metapopulations are a series of interconnected sub populations, some of which may contribute disproportionately large numbers of individuals to the metapopulation as a whole

Are extremely important in marine populations because of the life histories of many marine animals (larval dispersal).

Examples where metapopulation dynamics are important include a large barrier reef with nearby smaller reefs; an organism with a widely dispersing larval stage.

Metapopulation • Definition: A group of interconnected subpopulations

among which there is movement of individuals• Some subpopulations are sources of individuals that

move to other subpopulations• Other subpopulations are sinks, which means that

they may receive individuals from other subpopulations, but they are not sources (example, only juveniles disperse, but the subpopulation in question does not have individuals that reproduce successfully)

Metapopulation - interconnected group of subpopulations

Example: Intertidal arboreal snail, Littoraria filosa, occurs commonly on mangrove leaves in Queensland, Australia. Snails have planktonic larvae that are in the water for a month.

• In forests, snails appeared to be annuals that died every year.

•On isolated trees, snails did not die

•Predatory fly lives in forest and many of the snails in the forest don’t survive to reproduce.

Spatial Variation of Populations

Spatial distribution is a measure of spacing among individuals of a given area.

Scientists frequently study the spatial distrubution of organisms along with determining the density of organisms in a

given area.

Knowing the distrubution and density can the lead to interesting hypothesis about the environmental factors that are

impacting the population.

Example: barnacles

Spatial Distribution of Individuals

Random Uniform Aggregated

Ecological Processes at the community level

• Competition

• Predation

• Disturbance

• Parasitism

• Larval Dispersal

• Facilitation

COMPETITION

LIMITING RESOURCES

(1) Renewable - e.g., copepods exploiting diatom population

(2) Non-renewable - space on a rock exploited by long-lived sessile species

COMPETITIVE DISPLACEMENT - one species outcompetes another for a resource

COEXISTENCE - two species exploit different resources, some process allows two species to exploit same resource withoutdisplacement

Outcomes of Competition

Intermediate Disturbance-Predation Hypothesis

Low levels of disturbance or predation: Competitive dominant species takes over

Intermediate levels: Promotes coexistence, more species present

High levels: most individuals removed, reduces total number of species

SUCCESSION

Predictable order of appearance and dominance of species, usually following a disturbance.

SOME MODES OF SUCCESSION

(1) Early species modify habitat, which facilitates colonization by later species

(2) Late species exclude colonization of early species

(3) Early species hold space until death, then are replaced by late species, which do the same