option g.1: community ecology page 418. vocab recap community is a group of interacting populations...
TRANSCRIPT
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.