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 6 7

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 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.