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Biodiversity,Biodiversity, Species Interactions, Species Interactions,

and Population Controland Population ControlChapter 5

Chapter 3◦ Looked at ecosystem components and how energy

cycles within ecosystems

Chapter 4◦ Defined biodiversity. Looked at factors affecting

biodiversity and how it is measured.

Where we’ve been…Where we’ve been…

Chapter 5

◦ Look at how species interact with each other and how ecosystems respond to changes in environmental conditions.

Where we are headed…Where we are headed…

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

Species InteractionsSpecies Interactions

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

Interspecific CompetitionInterspecific Competition

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)

PredationPredation

When one organism lives on or inside of another organism◦ Parasite benefits, host organism harmed (not

immediately killed) Parasite dies if host killed

Symbiotic Relationships--Symbiotic Relationships--ParasitismParasitism

Interaction that benefits both species◦ Unintentional exploitation of the other organism

(not cooperation)

Symbiotic Relationships--Symbiotic Relationships--MutualismMutualism

Interaction that benefits one species and has little or no effect the other

Symbiotic Relationships-- Symbiotic Relationships-- CommensalismCommensalism

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

Population DynamicsPopulation Dynamics

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?

Limiting FactorsLimiting Factors

Range of ToleranceRange of Tolerance

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

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

Reproductive Strategies and Reproductive Strategies and SurvivorshipSurvivorship

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

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Population CalculationsPopulation 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

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Response to Ecosystem Response to Ecosystem ChangeChange 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

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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

Succession and Mt. St. Succession and Mt. St. HelensHelens

May 18, 1980 erupted violently

Deadliest and most destructive volcanic eruption in US history

Eruption reduced the height of the mountain by 1300 feet

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

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Article Reading and Article Reading and QuestionsQuestions 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?

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