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Outline. Density dependent population dynamics: logistic equation Cyclic and chaotic populations Life history strategies K vs r selection (MacArthur) C-S-R models (Grime) Examples of adaptive life history traits and strategies. Life table and population ecology resources.

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outline

Outline

Density dependent population dynamics: logistic equation

Cyclic and chaotic populations

Life history strategies

K vs r selection (MacArthur)

C-S-R models (Grime)

Examples of adaptive life history traits and strategies

life table and population ecology resources

Life table and population ecology resources

USGS interactive population model for spectacled eiders http://www.absc.usgs.gov/research/speimod/

Sample life table calculations from University of Cincinnati Clermont College: http://biology.clc.uc.edu/courses/bio303/life%20tables.htm/

Interactive models for human population http://simon.cs.vt.edu/geosim/IntlPop/

density dependent growth

Density dependent growth

As intrinsic rate of increase goes up, behaviour of model changes:

Carrying capacity: one equilibrium value for N

Stable limit cycles: N oscillates among several values

As R increases, number of values in cycle doubles (for 2.1<R<2.57)

Eventually (R>2.57) dynamics are CHAOTIC. Not random, highly density dependent, but unpredictable.

slide4

Time lags can also create cycles:

Resource availability changes with time and population size (eg herbivores and food source)

dN/dt=rN((K-N(t-T))/K)

Classic example: lynx and hares…

alee effect

Alee effect

Can get density dependent effects that work in the opposite direction, especially for small populations

For example: reduced reproduction if population is too small can accelerate decline to extinction. This “inverse density dependence” is called an Alee effect.

metapopulation

Metapopulation

A “population of populations”.

Dynamics driven by dispersal between patches (colonization) and extinction of sub-populations.

metapopulation1

Metapopulation

Usually more dispersal between close patches, less extinction in large or good-quality patches.

“Island Biogeography”

Small, poor patches may be “population sinks” (cannot sustain population on own; are maintained by dispersal from “source” populations.

summary

Summary

Demography affects current distributions, historical range shifts/spread, gene frequencies, and population structures.

Population dynamics important for commercial species: yield, growth, survival, etc.

Use population models to create management plans for both endangered and invasive species

Herbivory (eg stock production) can affect population parameters of range species: Riginos and Hoffman (2003). Journal of Applied Ecology 40:615-625.

life history strategies

Life History Strategies

Principle of allocation: individuals have limited resources to spend on growth, maintenance and reproduction

Life History Strategy: Pattern of resource allocation

(developed via natural selection)

Successful strategy maximizes reproduction, survival and/or growth in given environment

Assumption: there is a tradeoff between fecundity and survival. “Cost-benefit analysis”

examples of tradeoffs

Examples of tradeoffs

Current and future reproduction. Poa pratensis number of inflorescences in year one negatively related to number in year two

Colonization and competition. Large numbers of small seeds VS few large seeds.

examples of tradeoffs1

Examples of tradeoffs

Current and future reproduction. Poa pratensis number of inflorescences in year one negatively related to number in year two

examples of tradeoffs2

Examples of tradeoffs

Current and future reproduction. Poa pratensis number of inflorescences in year one negatively related to number in year two

Colonization and competition. Large numbers of small seeds VS few large seeds.

Root and shoot growth.

examples of tradeoffs3

Examples of tradeoffs

Current and future reproduction. Poa pratensis number of inflorescences in year one negatively related to number in year two

Colonization and competition. Large numbers of small seeds VS few large seeds.

Root and shoot growth.

Herbivore defense and competitive ability. Defensive chemicals or structures are costly to make and may reduce growth/reproductive output.

examples of tradeoffs4

Examples of tradeoffs

Current and future reproduction. Poa pratensis number of inflorescences in year one negatively related to number in year two

Colonization and competition. Large numbers of small seeds VS few large seeds.

Root and shoot growth.

Herbivore defense and competitive ability. Defensive chemicals or structures are costly to make and may reduce growth/reproductive output.

Growth and reproduction. Smaller growth increment or foliage production after large seed crop for trees

allocation to resource acquisition

Allocation to resource acquisition

Limiting resource model: there is a minimum level of a resource that is necessary for positive net growth

Can see tradeoff between resource capture mechanisms (eg root vs shoot)

Resource ratio hypothesis: mechanism for competition and succession.

Coexistence if two species limited by different resources

Shift in composition through succession because shift from limited soil resources to limited light

allocation to survival

Allocation to survival

Longer lived species delay reproduction

Longer life span means investment in maintenance and structure

Disturbed, ephemeral, and variable environments favour short life span

Less disturbed, moderate environments favour longer life span

Ephemeral- life span less than 6 months

Annual

life histories

Life histories

Ephemeral – life span less than 6 months

Annual – complete life cycle in one year

Biennial – vegetative one year, reproductive in following year

Perennial – lives for more than two years

allocation to reproduction

Allocation to reproduction

Monocarpy or semelparity: Single period of reproductive activity followed by death.

Polycarpy or iteroparity: Multiple episodes of reproduction in lifetime.

These two strategies have advantages and disadvantages...

allocation to reproduction1

Allocation to reproduction

Monocarpy or semelparity: mobilize large reserves, synchronize across region and swamp predators, minimal investment in structure (annuals).

Polycarpy or iteroparity: Multiple episodes of reproduction in lifetime, greater overall potential fitness, don’t have “all eggs in one basket”

classifying life history strategies

Classifying life history strategies

K and r selected species

A continuum between allocation to reproduction and to survival.

At one end: selection maximizes intrinsic rate of increase for population. This means seed output, dispersal, etc. This is r-selection. Occurs where mortality is DENSITY INDEPENDENT

At other end: selection maximizes competitive ability or survival to maintain population near carrying capacity. This is K-selection. Occurs where mortality is DENSITY DEPENDENT

characteristics of r vs k

Characteristics of r vs K

r selected species: variable climate, low competition, short life span, seed bank, seed dispersal, semelparous strategy. Type I survivorship. e.g. Cheatgrass.

K selected species: predictable climate, high competition, constant high population size, strong competition, no seed bank, delayed reproduction, iteroparous strategy. Type III survivorship. e.g. Sugar maple.

r c and s strategists

R, C, and S strategists

Another classification for life histories (Grime 1977)

R=Ruderal; colonizing species. Good dispersers, high reproduction. Temporary habitats with high resources. Allocation to reproduction. EG ‘weeds’

C=Competitive species. Good at obtaining resources. Predictable habitats with high resources. Allocation to growth. EG rhizomatous grasses.

S=Stress-tolerant species. Can persist in harsh, low resource environments. Allocation to maintenance. EG lichens.

r c and s strategists1

R, C, and S strategists

C

Species tend to have combinations of these traits.

CS

CSR

CR

SR

S

R

slide24

Lab: life cycle diagrams, matrix models, life tables, and their applications for management

Next lecture: metapopulations, life history strategies, allocation.