Option G.1: Community Ecology

Page 418

Vocab Recap

• Community is a group of interacting populations living together and interacting with each other in an area

• Distribution of organisms in communities is affected by abiotic and biotic features

Factors affecting distribution of plant species

• Temperature and water• Light• Soil pH • Salinity• Mineral nutrients • Turn and talk– Turn to your neighbor and discuss how theses factors

affect plant distribution– Are these factors abiotic or biotic?

Factors affecting distribution of animal species

• Temperature• Water• Breeding sites • Food supply• Territory• Turn and talk– Turn to your neighbor and discuss how theses factors

affect animal distribution– Which of these factors are biotic and which are abiotic?

Random Sampling • Suppose you wanted to determine the size of a population • You could count every organism, but that would be very

time consuming • Ecologists use a sampling method• They take a random sample and use it to estimate the

total number of organisms • Samples must come from all around the habitat

– Why? • In a truly random sample, each organism has an equal

chance of being selected for the count

Quadrat Method

• A quadrat is a square of a certain size • Organisms within the quadrat are counted• These counts are used to determine the

population size• How to solve: – Calculate the average number of organisms in your

sample quadrats– Multiply the average by the total number of

quadrats

Example

• A scientist wants to determine how many beech trees and maple trees are growing on a dune. The scientists measures the area and divides it into 20 quadrats. Using a random sample table, five sample squares are selected and trees counted. The table on the next slide shows the data.

Example – continued

• How many beech trees are there on the dune? How many maple trees?

Quadrat Beech trees Maple trees

1 5 10

2 8 12

3 4 9

4 6 7

5 3 4

Example – continued

• Take the average– Beech: 5.2– Maple: 8.4

• Multiply the average by the total number of quadrats – Beech: 5.2 x 20 = 104 – Maple: 8.4 x 20 = 168

Transect

• Commonly used for studying how the distribution of plants in an ecosystem is affected by abiotic factors

• Ecologists still draw quadrats and count the number of plant species of interest

• They also measure the abiotic feature (e.g. temperature, pH, light …)

The niche concept

• Every organism in an ecosystem has a particular role in that ecosystem– That’s the organism’s niche – Concept includes where the organism lives (spatial

habitat), what and how it eats (feeding activities) and its interactions with other species

– What’s your niche?

Spatial habitat

• Unique space in the ecosystem• Area inhabited by any particular organism • The ecosystem is changed by the presence of

the organism• Habitat loss is the greatest threat to

biodiversity on our planet – What’s causing this?

Feeding activities

• Affect the ecosystem by keeping other populations in check

• For example, green frogs eat aquatic larvae of mosquitoes, dragonflies, and black flies – Green frogs keep these insect populations in check

Interactions with other species

• Competition– When two species rely on the same limited resource– One species will be better adapted than the other

• Herbivory– A herbivore is a primary consumer (plant eater)

feeding on a producer (plant) – The growth of the producer is critical to the well-

being of the primary consumer – This is an interaction between plants and animals

Interactions with other species

• Predation– A predator is a consumer (animal) eating another

consumer (animal)– One consumer is the predator and the other is the

prey – The number of prey affects the number of

predators and vice versa

Interactions with other species • Parasitism

– A parasite is an organism which lives on or in a host and depends on the host for food

– The host is harmed by the parasite

– Ex: plasmodium is a parasite that causes malaria in humans (reproduces in the liver and RBC); part of its life cycle take place in mosquitoes – mosquitoes are the vector

Interactions with other species

• Mutualism – Two organisms living together where both

organisms benefit from the relationship – Ex: clown fish and sea anemones • Clown fish are brightly colored and live within the area

of the tentacles of the poisonous sea anemone • Clown fish are covered with mucus, which protects

them • Clown fish lure other fish; sea anemone eats the fish

and the clown fish eat the remains

Competitive Exclusion

• No two species in a community can occupy the same niche

• 1934; Russian ecologist G.F. Gause– Experiment with two different species of paramecium (P.

aurelia and P. caudatum) – When each species was grown in a separate culture they did

equally well– When the two were cultured together, with a constant food

supply, P. caudatum died out and P. aurelia survived• When two species have a similar need for the same

resources, one will be excluded

Fundamental niche vs. realized niche

• Fundamental niche– Potential mode of existence, given the adaptations

of the species • No competition from other species

• Realized niche– Actual mode of existence, which results from its

adaptations and competition with other species

Biomass

• Total mass of organic matter– Organic matter = carbon compounds (carbs, lipids,

proteins) • Since matter also includes water, which is not

organic, it has to be dried • Biomass is measured as dry mass or organic

matter of living organisms • Units = grams per meter squared per year – g m-2 yr-1

Measuring biomass at each trophic level

• How difficult is this?• There are tables and charts available which tell

you the biomass of animal according to its size or weight– Ex: trap a raccoon, weigh it, then find its biomass in

a table (raccoon should be returned to ecosystem) • There are tables for plant species, but it’s not

easy to determine the weight of a tall tree – What to do?

Measuring biomass – cont. • Measure the total area of the ecosystem• Divide the ecosystem into small areas & choose one plot to

sample• Measure the size of each plant species (height and diameter) • Cut down all trees and vegetation• Dry them out• Mathematical model to show relationship between weight

and height of each plant and its biomass • Sample other plots by measuring height and diameter

(cutting down is not necessary)

Measuring biomass – cont.

• If you are measuring the biomass of the ecosystem, then you would add in the animal species

• Process is repeated seasonally or yearly to study changes in biomass over time

Issues – Turn and Talk

• After measuring or counting organisms, we may fail to return them to the same ecosystem. Is there a moral principle involved here?

• In order to measure biomass, destructive techniques are used – trees are cut down and plants are destroyed. Is this unethical?

• Could the destructive sampling techniques described be explained as “moral relativism”?

Review

• List three factors that affect the distribution of animal species.

• Explain the competitive exclusion principle. • Describe one technique that ecologists use to

estimate accurately the size of a population of animals, including any calculations that need to be done.