Bio 201 Exam 1

What is ecology?

ecology- study of interaction between an organism and their environment

environment- interaction between an organism and other organisms of the same species (population), interaction between organisms of different species (community), and interactions between organisms and the abiotic components of their environment

Hierarchy of Complexity

atom- molecule- macromolecule- cell- tissue- organ- organ system- organism- population- community- ecosystem

cascade effect- eliminating or reducing top predators has a cascading effect down the food web

Global Climate Change

carbon, nitrogen, water, phosphorous, sulfur move in and out of biotic and abiotic environments

fossilized carbon that has been locked underground gets released into the atmosphere

Greenhouse effect- visible light gets absorbed by the earth’s surface while some gets readmitted back into the atmosphere as infrared light. greenhouse gases absorb some infrared light and keep some of it within the earth, keeping it warm. As more gases are released into the atmosphere, more heat gets trapped.

higher greenhouse gases means more light is retained into the atmosphere

Population Growth and Stability

Population size (N)

metapopulation- group of geographically separated populations that are linked by dispersal (individuals immigrating and emigration from the populations)

population numbers determined by birth and death rates and immigration and emigration rates 

uniform distribution- has equal spacing between individuals

random distribution- no pattern to spacing between individuals

clumped distribution- has distinct areas where individuals are close 

main factor in distribution is availability of resources 

life history trait- trait influenced by age specific survival and reproduction (evolutionary strategies to increase fitness) ex. age of maturation, number and size of eggs

Age pyramids 

Population Growth Model

Basic Assumptions of all models

  1. closed populations- no immigration or emigration 

  2. constant growth rate (birth and death rates)

  3. no age structure- population is sexless, pathogenic that can reproduce right after birth

Geometric Model Assumptions

  • non-overlapping generations (adults die before maturation of young)

OR

  • overlapping generations and discrete reproduction 

  • unlimited resources

discrete reproduction- adults only reproduce during specific times of the year 

Per capita growth rate = N(t+1) / N(t)

finding population of the next year

N(t) = N(0)y^t

curve of graph determined by y, per capita growth rate 

y- symbol for per capita growth rate “lambda” 

Exponential Model Assumptions

  • overlapping generations

AND

  • continuous reproduction throughout the year 

  • unlimited resources 

  • r is per capita growth rate 

r=lny   y=e^r

N(t)= N(0)r^rt

example - N(0) = 100; y=3

r=lny=ln(3)= 1.1 individuals per year 

What is the population after five years?

N(5)= (100)e^(1.1×5) = 24300 individuals 

both r and y are measured by year, if by month then divide by 12

r>0 = positive growth

r=0 = stable population

r<0 = negative growth

rate of population growth- net change (added or lost) in individuals to population over a certain time period 

net change = N/t

dN/dT= change in number/ change in time = per capita growth rate of increase x population size 

Logistic Model 

limited resources (food, space, mates)

carrying capacity- where populations level off at the max number of individuals the environment can support 

k is carrying capacity

net change 

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

Logistic model assumptions: overlapping generations and continuous reproduction, limited resources, constant carrying capacity

Population Stability and Regulation

if N>K, then the birth rate is higher than the carrying capacity

feedback loop- birth and death rate respond to increase/decrease in density relative to carrying capacity

Factors impacting population stability

  • per capita growth rate (r)

  • delayed density dependence 

  • stability of abiotic environment 

  • interaction with other species (predator and prey) 

  • increase in N = decrease in stability

time lags can cause delayed density dependence which can result in population cycles 

higher length in delay = higher instability

rescue effect- having other nearby patches increases the likelihood of recolonization of unoccupied patches 

sources- large patches that produce excess individuals that disperse away and colonize small, unoccupied sink habitats

sink habitat- one that has repeated extinction

small populations more vulnerable to extinction by random chance that all individuals will fail to reprodice 

stochastic effect- random environmental events impact small populations ex. golden toad went extinct because the puddles they breed in dried up so their eggs couldnt survive

inbreeding- individuals who breed that are closely related decrease genetic diversity, can lead to genetic drift

allee effect- lower populations size decreases fitness 

c- colonization rate

e- extinction rate

e/c <1 then metapopulation will persist over time

e/c >1 then metapopulation will not persist over time