Ecosystems, Food Chains, and Population Growth

Created April 2020 by Bree Latner, Offline version here
Video by Paul Anderson, also on his website Bozeman Science.

    An ecosystem is a level of organization in ecology that contains all of the of organisms and their environment. An ecosystem like the Greater Yellowstone Ecosystems consists of factors like grizzly bears and factors like geothermal pools and geysers. An ecosystem is supported by , which is a measure of how much biomass an ecosystem can produce. Primary productivity is measured in grams of per square meter per year. This shows us that that energy is being stored in organic matter. Producers take in and use light from the sun to turn it into or organic matter. The organic matter produced by primary productivity support all life in the ecosystem. The organic matter will allow that energy to flow from organism to organism as it passes through the . In a food chain, the energy and matter from primary production flow through as one organism eats organic matter of another organism. In ecosystems like, lake Ontario, at the base of a food chain are organisms like algae that produce organic matter using the energy from sunlight through photosynthesis. They form trophic level one or the . The second trophic level, , are organisms that eat primary producers. Algae is eaten by amphipods. The organic matter made by the primary producers, algae, transfers energy to the primary consumers, amphipods. The amphipods are eaten by fish like rainbow smelt, forming the third trophic level in the food chain, the . Those smelt are then eaten by fish like salmon, and the energy stored as organic molecules flows to the fourth trophic level, the , or 3rd level consumer. Food chains are linear; in an ecosystem there are many interconnected food chains, called a . The energy flow through a food web supports all life in an ecosystem. This allows populations of organisms to grow. Population growth is generally if there aren’t any limiting factors. As the population grows limiting factors arise that shift that growth to growth, which is limited growth. Limitations on growth can be , meaning the limit on how the population can grow has to do with the option density, or size of the population in the ecosystem competing for resources. Limitations can also be . These are things like environmental conditions like weather and geological conditions that limit the rate of population growth. Logistic growth usually reaches a limit or . This tells the population size that can be supported in an ecosystem given limiting factors. The is the maximum number of that population the ecosystem can support. In the wolf population at Yel-lowstone National Park we see that the average number of wolves is about 140. That is the average maxim population the land can support. When more than one species relies on the same resources or are have a predator/prey relationship, the species population growth will be limited by . Wolves in Yellowstone National Park have a diet high in elk. As the wolf population , the elk population decreases. As the elk become more scare the wolves population growth is limited by the number of elk available to support them. This predator/prey relationship will cause both populations to reach an , as their population numbers are dependent on each other. Human produced climate change is caused by rising levels of in the Earth’s atmosphere. Rising levels of carbon dioxide trap energy from the sun in the atmosphere and cause global temperatures to rise. In Yellowstone National Park, the white-bark pine tree population produces pine nuts. In this food chain the white-bark pine is a . The pine nuts are a food source of squirrels. Squirrels hide those pine nuts in stashes called middens. Grizzly bears find those middens and eat the pine nuts before they hibernate in the winter. Climate change has caused a of the global climate which is limiting the population of white-bark pines. This effect is seen passed through the food chain as squirrels and then bears lose a food source. In this food chain, human impact is predicted to cause not only a in the white-bark population, but also the squirrel, and grizzly bear population.