Population Ecology notes

Honors Biology:  Chapter 36 Notes - Population Biology

1. Population Characteristics

   1. Population Size (N) - # individuals of the same species living in the same geographical area

   2. Population Density - # individuals per unit area or volume (i.e how crowded) (d=N/A) 

   3. Population Distribution - The pattern of dispersal

1. Clumped    

2. Uniform   

3. Random   

II.  Mortality Patterns

1. Life Table - Gives the probability at birth of being alive at age X for a specific cohort (= group of individuals born at the same time).    

1.  What percentage survived until age 10? 99.3%

2.  During which age interval is the survival rate closest to 50%? 80-90  

3.  During which age interval is the survival rate the highest? 10-20    

4.  During which age interval does the greatest number of people die? 80-90     

B.  Survivorship - the probability of an indiv. surviving to a certain age  

-3 Types (or models):

→ Which survivorship type best fits each of the following actual life patterns?   

  Type I             Type III               Type II

III.  Pop. Growth Models

1. Factors affecting future population growth:

1. births, immigration (+)    

2. deaths, emigration (-)  

2. per capita rate of increase (r) -  Average contribution of each individual to population growth. (usually det. by B.R and D.R)

Ex. What is “r” for a pop of elephants, where during the year 10 births and 2 deaths occur?   

N = 100

q_x = 0.02 (2 deaths/100 pop.)

M_x = 0.1 (10 births/100 pop.)

→ Formula: r = M_x - Q_x

_{r = 0.1 - 0.02}

  _{= 0.08 elephants/year}

Where:

  *r = per capita rate of increase

  *N = population size (needed to calculate death rate and birth rate)

  *q_x = death rate (per capita)

    *M_x = birth rate (per capita)

  *x = time interval 

🡪Is this population growing?    yes 

🡪Is it growing fast?   sort of… especially for elephants 

3. Exponential Growth Model

   1. Number of individuals added each generation increases as total number of individuals increases

   2. Population is dependent on (r) and (N)

   3. Curve: (“J” curve)

4. Equation  - G = rN   

Where:

*dN = Change in pop. numb.

*dt = Change in time

*r = rate of nat. increase

*N = current pop. numb

[d = “change in” (think d = ▲)]

Ex. If for a pop. N = 50, which will be larger after one generation?    r = 2.4  OR   r = .5 ?

4. Logistic Growth – Pop. growth slowed by environmental resistance (=limiting factors)

1. Limiting Factors - causes pop. growth to slow down   

1.  Abiotic - non-living 

2. Biotic - living factors 

2. Curve:(“S”- Shape)

3. Equation - G = rN (K-N)/K 

4. K = Carrying Capacity –  Max population size that the environment can support 

🡪 The closer N  is to K , the more environmental resistance will occur.

IV.  Regulation of Pop. Size

1. Density-Dependent    

   1. Biotic factors affecting pop. size  

   2. Pop. more affected as density increases. 

  Examples: competition for resources, predation, disease

2. Density-Independent- Abiotic factors affecting pop. regardless of density. ex severe weather, natural disasters   

3. Predator-Prey Cycling. Example  - ____    

4. Types of Reproductive Strategies

   1.  Semelparity (r-selected) 

r= reproduction, Type lll

a.   Female repro. once/year, then die 

b.  many offspring 

c.   high infint mortality/minimal parental care 

d.  small body/ short developmental period 

🡪Ex.    annual weeds, insects

2. Iteroparity  (K-selected)

a.  longer devel. period/larger body size 

b.  more energy for parental care 

c.  fewer offspring, repeated reproduction 

d.  lower infant mortality

                           e. slower population growth 

🡪Ex.    humans elephants bold eagle

5. Why is it important for Wildlife Biologists to know what r is for a species?   Sustainable Resource Management (36.8)  

V.  Human Population Growth

1. Growth is logistic but has not reached stable equilibrium

2. Demographic Transition – from high D.R and B.R to Low D.R and B.R.

female education most important factor   

3. Age Distribution –   can be used to predict future pop. growth