Population Ecology Part IV

Why/how population grow is important why?

• Conservation

• Management

Population growth models (more dynamic)

• Describe changes in population size over time.

• Parameters from the life table are incorporated.

• Future population changes are determined through projections and predictions.

Life table (are what)

• Summarize structure of populations 

• Tells with age classes contribute the most to population growth. 

• They provide a static “picture” of the population. 

Factors affecting Population growth

Environment, age, structure, # of reproduction events/patterns, mating sys, social behavior. 

Age impacts

• Survivorship

• Dispersal 

• Mortality 

• Fecundity 

Determined Growth

Individuals stop growing after a certain age.

Once mature, fecundity is constant, may cause between age 

Indetermined Growth

Individuals grow continually throughout their life and fecundity varies with age. 

(ex; fish, reptile, perennial plants) 

Fecundity

Number of offspring produced increases with age. 

Iteroparous (Iteroparity)

Species have multiple reproductive events in a specific age period/lifetime. 

(Atlantic salmon)

Semelparous (semelparity) 

Species with a one-time reproductive event. All energy goes into one reproductive event. 

(ex: Sockeye Salman) 

Discrete Generations

Each generation is separated in time and clearly identifiable.

Population growth model (ecology)

Models are mathematical descriptors or graphical representations used to predict/describe an ecological process OR concept. 

Changes in population size (equation)

N_t+1=N_t+B-D+I-E

Where: 

N_t= Population size at time ‘t’ 

B= Total Birth 

D= Total Death 

I=Total immigrants 

E= Total emigrants

Closed Populations

Changes in abundance (N) are detered by births (B) and death (D).

Open populations

Changes are further influenced by emigration (E) and immigration (I).

Types of Discrete Models

Geometric Growth Model

Types of Overlapping Generations Model

1) Exponential Growth Model

2) Logistic Growth Model

Geometric Population Growth Model

Density Independent

Population Size changes by constant ratio/growth rate.

N_t=N₀λ^t

Where: 

λ= Growth rate (the Finite rate of increase) (constant) 

λ=N_t+1/N_t 

Exponential Population Growth Model 

Equation: 

N_t=N₀e^rt

e= mathematical constant (2.718) (constant)

Relationship Between λ and r

r=ln(λ)

Where: 

• r is constant

• Density-independent growth model. 

Exponential Population growth Model (double/triple…) equation

T_double=In(2)/r