1. Biodiversity, Species Interactions, and Population Control
Chapter 5 1

2. Where we’ve been… Chapter 3 Chapter 4
Looked at ecosystem components and how energy cycles within ecosystems
Chapter 4
Defined biodiversity. Looked at factors affecting biodiversity and how it is measured.

3. Where we are headed… Chapter 5
Look at how species interact with each other and how ecosystems respond to changes in environmental conditions.

4. Species Interactions
Five Major Ways that Species Interact with one another:
1. Interspecific Competition
2. Predation
Symbiosis (two species living closely together)
3. Parasitism
4. Mutualism
5. Commensalism

5. Interspecific Competition
When two or more species interact to gain access to the same limited resources (food, water, light, space)
Intraspecific: same species competing for resources
Resource partitioning: species evolve traits to minimize competition with other species
As our footprint grows larger, we are impacting species even more (habitat loss)
Humans competing with other species for space and access to resources

6. Predation
When one member of a species feeds on a member of another species
Predator-prey relationship
Predators and prey often co-evolve traits that either allow them to find prey or hide from predators better
Predators play important roles in ecosystems (help to keep other species in balance)

7. Symbiotic Relationships--Parasitism
When one organism lives on or inside of another organism
Parasite benefits, host organism harmed (not immediately killed)
Parasite dies if host killed

8. Symbiotic Relationships--Mutualism
Interaction that benefits both species
Unintentional exploitation of the other organism (not cooperation)

9. Symbiotic Relationships-- Commensalism
Interaction that benefits one species and has little or no effect the other

10. Population Dynamics
Population: group of interbreeding individuals of the same species
Most organisms live together in clumps
Changes in population size influenced by:
Births and deaths
Immigration and emigration
Population change= (births + deaths) – (immigration + emigration)
Age structure diagrams can also be used to describe organism populations
-identify if population is growing, stable or declining

11. Limiting Factors
Populations have a range of tolerance. A set of physical and chemical conditions that they will thrive under.
Small variations in a population will exist due to genetic differences
“optimal range of tolerance”—conditions in which most organisms survive
Limiting factor principle: too much or too little of any physical or chemical factor can limit or prevent growth of a population
Examples of limiting factors?

12. Range of Tolerance

13. Population density: number of individuals found in a particular area
Carrying capacity: maximum number of individuals an ecosystem can support.
Environmental resistance: combination of all limiting factors determines carrying capacity
Exceeding carrying capacity causes population to crash
Overshoot and die off
Population density: number of individuals found in a particular area
Density dependent limiting factors
Parasitism, infectious disease, competition
Density independent limiting factors
Weather events, fire, pollution, habitat destruction

14. Reproductive Strategies and Survivorship
R-strategist (type 1)
Many small offspring with little or no parental care
Large losses of young offspring, so produce large numbers to compensate
Examples: algae, bacteria, insects, some fish species
K-strategist (type 3)
Reproduce later in life, few offspring
Longer lifespan, mature slowly with parental care
Examples: mammals, birds
When graphed these two reproductive strategies produce unique survivorship curves
Classified as type 1, 2 or 3 depending on mortality rates

15. Type 1: low infant mortality and high survival
Type 2: constant decline
Type 3: high infant mortality few reach adult

16. Population Calculations
Annual Growth Rate
(CBR-CDR)/ 10 = % growth
** Does not include immigration or emigration
Change in Population per year
Population change= (births + deaths) – (immigration + emigration)
Population Density
(Number of individuals) / (area sampled)
Doubling Time
70/ annual growth rate = doubling time of a population
Birth and Death Rates
(births or deaths per year) / (Total Population)
**Crude birth and death rate multiply by 1000

17. Response to Ecosystem Change
Ecological Succession: gradual change in species composition in an ecosystem after a significant disruption
Primary succession: gradual establishment of living organisms in lifeless areas where there is no soil or sediment (aquatic)
bare rock, parking lots, new ponds or reservoirs, cooled lava
takes a very long time
Secondary succession: series of communities and ecosystems develop in places containing soil or sediment
abandoned farmland, burned/logged forests, polluted streams, flooded land
can relatively happen quickly

19. Succession increases species richness and complexity of food webs
enhances energy flow and nutrient cycling which promotes increased biodiversity
does follow an unpredictable path
resilience of ecosystems: ability through succession to rebound to previous state after significant disturbance
rainforests highly complex and diverse, very difficult to return to previous state
“Ecological tipping point”—ecosystems won’t recover when past this point

20. Succession and Mt. St. Helens
May 18, erupted violently
Deadliest and most destructive volcanic eruption in US history
Eruption reduced the height of the mountain by feet

21. The Mt. St. Helens National Volcanic Monument was created to preserve the volcano as well as provide the land for scientific study.

23. Article Reading and Questions
Read the article: Mt. St. Helens 30 Years Later
Answer the following questions.
Describe the impact of the MSH eruption on the surrounding ecosystem. Give specific details.
Describe how succession is reshaping the MSH ecosystem. What has been observed in the past 30+ years?
What are the concerns with the MSH ecosystem looking toward the future?