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Types of Interactions
• Competition happens when two or more species depend on the same food source or any limited resource.
• Animals that feed on other animals are called predators.
• Sharks in Sable Island’s offshore waters are known to eat seals.
• The sharks are called predators and the seals are prey.
• In symbiosis, at least one member benefits from the partnership.
• A remora is a small fish that follows sharks around and eats their scraps.On Sable Island near Nova Scotia, gray seals and
harbor seals both feed on sand lances.
Populations• A population is a group of
individuals of the same species living in a given area.
• Populations change over time.• The change in size of a population over time is called its growth rate.
Invasive species• Recently, European green
crabs have been found in the United States.
• The arrival of the green crab is cause for concern.
• Green crabs eat many types of organisms including clams, mussels, and the young of other crab species. How might European
green crabs be harmful to U.S. ecosystems?
Pollutants
• A pollutant is something that causes harm to a living thing.
• Sulfur dioxide is a chemical that is a good example of a pollutant.
Pollutants
• Sulfur dioxide can make breathing difficult even for healthy people.
• It reacts with water in the atmosphere to make acid rain.
• Acid rain kills trees and harm life in lakes, ponds, and streams.
Pollutants
• Three things often determine how harmful a pollutant is:
1. the pollutant’s ability to cause harm;2. the amount of pollutant in air, water, or soil;3. how long the pollutant stays in air, water, or
soil.
Toxins in the food chain
• Human activities create toxic pollutants (toxins).
• Food chains concentrate some toxins into the tissues of animals.
Toxins in the food chain• When carnivores eat many herbivores, they
accumulate toxins in their tissues.
Water quality
• We protect the health of freshwater ecosystems by testing the water.
• Common tests include:– temperature, turbidity, dissolved oxygen, pH
Water quality
• To learn about the water quality of a pond, first make careful observations. – What does the pond water look like or smell
like? – What animals and plants are living in the
pond? – Where is the pond located? – Are there houses or farms nearby? – Is the pond near a factory?
Water quality
• The turbidity test measures the cloudiness of water.
• If the water is too cloudy, sunlight is blocked, and pond plants do not grow well.
The secchi disk is lowered into the water until the black and white panels are no longer visible.
Water quality
• The water temperature of a pond is measured three or more inches below the surface of the water.
• The higher the water temperature, the less oxygen there may be in the water for living things.
Water quality
• The pH scale ranges from 0 to 14.
• Pure water is pH 7 (neutral).
• Most organisms in ponds function best when the water pH is near 7.
Water quality
• Water quality is better when dissolved oxygen levels are high.
• Oxygen is needed by most organisms living in the pond.
Water quality
• Nitrates and phosphates are chemicals that can enter ponds from farms, fertilized lawns, or septic tanks.
• Excess nitrates or phosphates endangers the health of the pond ecosystem.
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