1. Population and Community Ecology

2. Complexity of nature
Population: all inviduals that belong to the same species and live in a given area at a particular time
Community: all of the populations within a given area; used to see how species interact with one another
Ecosystem: all of the biotic and abiotic components in a particular location; used to study flows of energy and matter
Biosphere: all of earth’s ecosystems; used to study movement of water, air and heat around the globe

3. Population Ecology
“study of factors that cause populations to increase or decrease
Population Size
a. (births and immigration) - (deaths and emigration)

4. Population Characteristics
Population size
Population density
Population distribution
Population sex ratio
Population age structure

5. Population Size
Total number of individuals within a given area at a particular time
Dependent upon density-dependent and density-independent factors
Density dependent
- depends on how dense the population is
- limiting resources
ex) plants – nitrogen and phosphorus
animals - food
- carrying capacity( K): helps in predicting how many individuals a population can
sustain
Limiting resource: a resource that a population cannot live without and which occurs in quantities lower than the population would require to increase in size

6. d. density-independent factors - does not depend on how dense the population is - ex) tornado, floods, fires

7. Population Density Number of individuals per unit of area
Helps scientists estimate if a species is rare

8. Population Distribution
How individuals are distributed throughout
Random, uniform, clustered

9. Population Age Structure
How many individuals fit into a particular age category
Predicts how rapidly a population will grow
Population with a large proportion of old individuals are with a large population of individuals that are too young to reproduce will produce fewer offspring that a population that has a large proportion of individuals of reproductive age

10. Population Growth Models
Growth rate – (births – deaths) in a given time period
- intrinsic growth rate
* unlimited resources available (r)
* high population growth rate
b. Exponential growth model
- rapid growth
- j shaped curve
- continuously increase population growing at a fixed rate
Exponential growth: under ideal conditions, the future size of the population depends on the current size of the population, the intrinsic growth rate and the amount of time over which the population grows
* Real populations can grow exponentially at first but over time they will reach a carrying capacity

11. c. Logistic growth model (k) - incorporates limits on population growth (limiting resources) - s shaped curve - predicts population growth subject to density-dependent constraints - overshoot - die-offs (population crash) - predation (lynx and the hare)
Initially exponential and then reaches carrying capacity

12. Reproductive Strategies and Survivorship curves
K-selected species (elephant)
- low intrinsic growth rate
- large organisms, late reproductive maturity, produce few offspring, provide parental
care
b. R-selected species (dandelions, house mice)
- high intrinsic growth
- rapid population growth with overshoots and die-offs
- small organisms, early reproductive maturity, reproduce frequently with lots of offspring,
little or no parental care
Population size most commonly increases through reproduction
Elephants are example of k-selected species
Endangered k-species cannot respond quickly to efforts to save it from extinction

13. c. Survivorship curve – distinct patterns of survival over time
K-selected species: high survival rates throughout most of their lifespan but as they get older, they start to die off (TYPE I) - elephant
R-selected species: low suvivorship early in life and very few reach adulthood (TYPE III) - mosquito
Squirrels experience TYPE II where there is a constant decline in survivorship throughout their lifespan

14. Competition “struggle of individuals to obtain a limiting resource”
Competitive Exclusion Principle
- two species competing for the same limiting resource cannot coexist
- having the same realized niche can lead to extinction of one species

15. b. Resource partitioning - two species divide a resource based on behavior and morphology - ex) birds that eat different seeds - 3 types * temporal * spatial * morphological
Temporal – utilizes same resource but at different times of the day
Spatial – using different habitats for the same resource
Morphological – darwin’s finches
Overall: reduces competition for limiting resources

16. PREDATION One species as a resource of another species Four types
- true predators
- herbivores
- parasites
- parasitoids
C. lynx-hare relationship
D. Defenses
- hiding, reduced movement, chemical toxins, thorns, camouflage
True predators – kill their prey and consume most of what they kill
Herbivores – consume plants as prey; eat only a small fraction without killing it
Parasites – live in or on an organism (host); rarely cause death of host
Parasitoid – lays eggs within host and they slowly consume host from inside out leading to death

17. Mutualism
“benefits two interacting species by increasing both species’ chances of survival or reproduction”
Examples
- pollination
- coral reefs and algae
- acacia trees and ants
Acacia tree provides a home for the ants and the ants protect the tree from any predators (herbivores or other plants)

18. Commensalism
“one species benefits but the other is neither harmed nor helped”
Example
- birds using trees as a perch

19. Keystone Species
“species that plays an important role in its community” Exist in low numbers Types a. predators b. sources of food c. mutualistic species d. provider of other essential services

20. a. sea stars (Pisaster ochraceus) b. flying fox
Examples
a. sea stars (Pisaster ochraceus)
b. flying fox
c. beavers (ecosystem engineer)
Sea stars – prey on mussels which clears space for other species to attach on the rocks
Flying fox – only pollinator and seed disperser for hundreds of tropical plant species
Beavers – creates habitat for other species (ecosystem engineer); create dams that convert narrow streams into large ponds, ponds may flood causing trees to die and then creating a habitat for animals that rely on dead trees

21. Succession
Ecological succession – predictable replacement of one group of
species by another group of species over time
Primary Succession
a. surfaces that are devoid of soil
Steps:
Bare rock is colonized by algae, lichens (can survive with little or no soil)
Once these are dead, they become organic matter that allows soil to be created
Soil develops on bare surface and can now allow for deep rooted plants to survive
First, there are mid-successional plants such as grasses and wildflowers (helps bring up nutrients in the soil)
New species colonize the area and outcompete the mid-successional plants
Eventually, it is colonized by bigger trees and plant species

22. a. areas that have been disturbed but have not lost their soil
Secondary Succession
a. areas that have been disturbed but have
not lost their soil
b. pioneer species
Pioneer species: trees such as the aspen because of their ability to colonize new areas rapidly and grow well in full sunshine (these trees can disperse easily as well)

23. Factors affecting Species Richness
Determined by
a. colonization of the area by new species
b. speciation within the area
c. losses from the area by extinction
Factors above are influenced by
a. latitude
b. time
c. habitat size
d. habitat distance
Species richness: # of species in a given area

24. Latitude
a. the further away from the equator, the number of species decline
b. no known reason
Time
a. longer a habitat exists, the more species there will be (colonization,
speciation and extinction)

25. Habitat size and distance a. “Theory of Island Biogeography”
- size: larger habitats contain more species
* dispersing species are more likely to find larger habitats
* larger habitats are less prone to extinction
* larger habitats contain wider range of environmental conditions
- distance:
* islands further from land contain fewer species
Species are more likely able to disperse short distances than they are longer distances