Notes - Population, Community and Ecology - The is the source of energy for our planet. Whether we are talking about heat energy, light energy or energy. We can show how this energy from the sun moves through ecosystems using what is called a. - The energy from the sun along with nutrients like,,, and are moving through the ecosystem through capture and ingestion by each organism. This process starts through a chemical reaction called. Photosynthesis occurs when, (usually in a plant) use the sun s light energy to combine CO 2 ( ) with H 2 O (water) to make sugar (glucose) and O 2 ( ). The reaction looks like this; - Once consumers eat the plant they use the glucose to create energy back for themselves through a process called cellular aerobic respiration. The reaction looks like this; - A describes what position the organism occupies in relation to the order of nutrient and energy transfer. 1
- are the first level. They capture the energy from the sun by turning light into chemical energy. are the second level as they eat producers for their energy and nutrients, and carnivores occupy the third level and upper levels as they eat herbivores. occupy all of the consumer levels (2, 3, and up). - Energy flows in a simple food chain. At each level of the food chain, about of the energy is lost in the form of heat. Therefore, as you move up the food chain, there is less energy available. - Food webs are multiple food chains showing the complexity of the ecosystems nutrient and energy pathways. 2
- are another way to depict the transfer of energy and nutrients. They are in the shape of a step pyramid and depict the energy at each level. Only about 10% of the energy makes it to the next level. - Organisms can move to new ecosystems through a way called primary succession. Primary succession is when an initial organism called a pioneer species populates a previously barren environment. - Pioneer species are often lichens or mosses as they are able to survive by breaking down rocks to gather nutrients and need minimal water and light. The smaller size of this organism helps by limiting the amount of water and nutrients needed. - This organism changes the environment by releasing nutrients from the rocks and also adding nutrients when it dies, allowing other species to arrive and thrive. This succession of new species arriving continues until a stable equilibrium occurs between all of the organisms, creating a complex community called a climax community. 3
- Secondary succession occurs in environments that have favorable conditions to be colonized, but a large disturbance like a fire or flood, have wiped out the previous occupants. The soil has already been developed so new organisms will populate the area and re-establish a climax community much faster than in primary succession. Population Growth - Populations are a group of like organisms (same species) that live in the same area. If the necessities of life are being met, then a given population will begin to grow rapidly. The larger it gets the faster it grows. This is known as. This cannot continue indefinitely as on our planet there are limitations that stop population growth. A more realistic growth curve is called a growth curve. - Once the is reached, the population will stay at this level due to natural controlling factors. Examples of these controlling factors are lack of food,, predation, and. - These examples of controlling factors can be looked at more accurately by dividing the factors into two categories; density-dependent and density-independent limiting factors. Density Dependent Factors - Density dependent factors only affect large crowded populations and have minimal affects on small populations. These are the four factors; competition, predation, parasitism, and crowding. - when populations are high in plants or animals, the resources available become split between many individuals. This will lead to less for everyone and ultimately drive the population down through increased death. 4
- all heterotrophs are predators to some species and prey to others (except humans). This causes predators and prey to be intricately connected, knowing each other s strengths and weaknesses. This results in predator/prey cycles to be set up naturally to control each other s populations. - parasites often work like predators. They weaken and may kill their host. If numbers of prey (hosts) are high, then spreading is much easier. - Crowding and Stress most animals have a built in need for a certain amount of area. This may be to have enough area to hunt or breed. If the population is too high and animals start to on each other s territory, will often occur. This leads to animals being. Too much stress can harm animals by causing weakened systems, less eating, and less. Density Independent Factors - Density Independent factors occur regardless of population sizes.,, cold weather, and are examples. These occurrences can happen at any time regardless of population size. Many smaller animals like arthropods are very susceptible to density independent factors. An example would be a population of aphids living on a rose bush. A large rainstorm can wipe out the population at any time. 5