Option g 1 community ecology
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Option G.1: Community Ecology - PowerPoint PPT Presentation

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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 .

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Vocab recap
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
Factors affecting distribution of plant species

  • Temperatureand 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
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
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
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


  • 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
Example – continued

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

Example continued1
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


  • 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
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
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
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
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 species1
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 species2
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 species3
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
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 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


  • 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
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
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 cont1
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
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”?


  • 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.