Download LIMITING FACTORS and more Study notes Dynamics in PDF only on Docsity!
LIMITING FACTORS
OBJECTIVES:
KEY TERMS:
NOTES:
- to learn about various limiting factors that influence population dynamics
- to investigate which factors affect yellow perch in Lake Winnipeg
LIMITING FACTORS
All living things need food, water, shelter and space to survive. Aas long as organisms have all of these things available to them their population will continue to grow. However, populations cannot grow forever. Some form of environmental resistance will stop the population’s growth. The form of environmental resistance is called a limiting factor since it limits the population. However, limiting factors may also increase a population. We will look at many different limiting factors and classify them into density independent factors and density dependent factors.
- natural disasters: disasters caused by nature
- density: organisms per unit area
- toxic: poisonous
- tail races: area of water located behind a dam
- aquatic: taking place in or on the water
- penetrate: to enter or force a way into
- depletion: the use or consumption of a resource
- turbid: degree of cloudiness of water
- tributaries: a stream that flows into a larger stream or other body of water
- invasive: moves in without right or permission, intrusive
TASKS:
Read the notes on limiting factors. Then, using the knowledge you have gained, read the next set of notes to find all of the limiting factors that affect yellow perch in Lake Winnipeg. Using the work sheet provided on page 4, try to identify as many limiting factors as possible and classify them as density independent or density dependent factors. Then answer the questions on pages 4 and 5.
DENSITY INDEPENDENT FACTORS
Density independent factors can affect a population no matter what it’s density is. For example: natural disasters, temperature, sunlight, human activities, physical characteristics and behaviours of organisms affect any and all populations regardless of their densities. Natural disasters such as droughts, floods, hurricanes and fires can be devastating to aquatic life. For example, a severe drought could lower the water levels of Lake Winnipeg and decrease its carrying capacity. Thus, the fish population would decrease. Temperature influences the activity and growth of organisms. Temperature also determines which type of organisms can live in a lake. Usually, the higher the water temperature, the greater the activity in a lake. However, all aquatic species have a preferred temperature range. If temperatures vary too much out of this range the species will either die or move to a different location. Temperature also influences the chemical properties of water. The rate of chemical reactions in the water increases as temperature increases. For example, warm water holds less oxygen than cool water, so even though there is more activity in warm water there may not be enough oxygen for the activity to continue for long periods of time. Sunlight can only penetrate to a depth of 30 meters in water. Thus most phosotsynthesis in aquatic environments occurs near the surface. This means that most plants cannot grow if they are at the bottom of a deep lake. Human activities can also affect population dynamics. For instance, lake sturgeon spawn in fast water and sometimes use the “tailraces” of hydroelectric dams. However, the water level in this location often drops suddenly and the eggs die because they become exposed. Physical characteristics of organisms can affect their population. Many organisms have adapted and evolved in order to increase their chance of survival. For example, some species of fish have colored markings to warn predators that they may be toxic. Or, some species use camouflage colors to help them hide and avoid being eaten. Behaviours of organisms can also affect their population. For example, some species migrate to find new food sources or to mate. Some organisms create societies or feeding territories. For instance, white bass live in schools and work together to drive emerald shiners to the surface for feeding. Some species may have mating or courtship behaviours that affect their population.
DENSITY DEPENDENT FACTORS Density dependent factors can only affect a population when it reaches a certain density. For example, competition, predation, disease, parasitism, crowding, and stress are all factors that only affect populations with high densities. Competition can occur between many organisms that live in the same habitat. Resources are limited in a habitat so organisms must compete for food, water, space, and shelter. For example, both northern pike and walleye prey on yellow perch and so they compete for the same food source. However, this competition is only apparent when the populations of northern pike and walleye have high densities OR the population of yellow perch has a low density. Predation occurs when the population density of predators is high. The predators will consume their prey and increase their own population. However, the population of the prey will decrease. On the other hand, the lack of predation (when the population density of predators is low) will cause problems for the prey’s population. When there are few predators, the prey’s population increases very quickly and this can lead to the depletion of resources and increase disease. Disease in a population increases with the density of that population. High densities makes it easier for parasites to find hosts and spread the disease. Parasitism is a relationship in which one species benefits at the expense of the other. A parasite is an organism that lives in or on another organism (called a host) to get nourishment. While the parasite benefits from this relationship the host is harmed or killed. Crowding only occurs at high densities. Over-crowding can cause depletion of resources, disease and stress. Stress usually has a negative effect on populations. Stress can make organisms weak and more prone to disease.
QUESTIONS:
Explain the difference between density independent and density dependent limiting factors. (2 marks)
From the previous article “Yellow Perch in Lake Winnipeg”, identify and describe as many limiting factors as possible and classify them as density independent or density dependent. (10 marks)
Density Independent Limiting Factors:
Density Dependent Limiting Factors:
(Out of 30 marks)
- Each of the statements below involves a situation that will affect the growth of a population. Classify each of the statements as DD (density dependent) or DI (density independent) and give a reason for your choice. (18 marks - 2 each)
a. Rainbow smelt and yellow perch attempt to occupy the same area. The more aggressive smelt survive; the perch do not.
b. A severe flood brings a lot of sediment and silt into Lake Winnipeg. The turbidity of the lake increases greatly.
c. A drought decreases the water level in Lake Winnipeg. The carrying capacity of the lake decreases.
d. Due to the introduction of rainbow smelt, Lake Winnipeg becomes crowded and some fish species do not survive.
e. Since northern pike prey on yellow perch, an increase in the perch population causes an increase in the pike population.
f. Many fish die due to an increase in water temperature.
g. Due to over-fishing, the number of walleye in Lake Winnipeg decreases.
h. A population is growing quickly when parasites cause disease to spread quickly.
i. Since lake sturgeon migrate long distances to spawn, many do not survive the trip.
- Each of the statements below involves a situation that will affect the growth of a population. Classify each of the statements as DD (density dependent) or DI (density independent) and give a reason for your choice. (18 marks - 2 each)
a. Rainbow smelt and yellow perch attempt to occupy the same area. The more aggressive smelt survive; the perch do not.
DD - competition between species only occurs at certain densities
b. A severe flood brings a lot of sediment and silt into Lake Winnipeg. The turbidity of the lake increases greatly.
DI - natural disasters affect all populations regardless of density
c. A drought decreases the water level in Lake Winnipeg. The carrying capacity of the lake decreases.
DI - natural disasters affect all populations regardless of density
d. Due to the introduction of rainbow smelt, Lake Winnipeg becomes crowded and some fish species do not survive.
DD - crowding only occurs at certain densities
e. Since northern pike prey on yellow perch, an increase in the perch population causes an increase in the pike population.
DD - predation only occurs at certain densities
f. Many fish die due to an increase in water temperature.
DI - temperature affects all population densities
g. Due to over-fishing, the number of walleye in Lake Winnipeg decreases.
DI - human activities affect all population densities
h. A population is growing quickly when parasites cause disease to spread quickly.
DD - parasitism only affects certain population densities
i. Since lake sturgeon migrate long distances to spawn, many do not survive the trip.
DI - behaviours of organisms affect all population densities
