Upload
dwight-shepherd
View
225
Download
0
Tags:
Embed Size (px)
Citation preview
Factors Affecting Population Change
Exponential Vs. Logistic Growth
Two Strategies for Growth
1. “r-strategists”: Spawners! Characterized by exponential growth, which results in temporarily large populations, followed by sudden crashes in population size.
Ex. Insects, bacteria, some plants
live in unpredictable and rapidly changing environments
Reproduce quickly when conditions are favorable External Fertilization Many offspring: small, mature rapidly, no parental
care
Two Strategies for Growth
2. “K-strategists”: Brooders! Characterized by a high degree of
specialization. Ex. Trees, whales, tigers, etc.
Live in stable and predictable environments Can compete effectively Reproduce late in life Internal Fertilization Few offspring: large, mature slowly, often much
parental care
Density Dependent Factors
Factors that influence population regulation, having greater impact as population density increases or decreases Struggle for survival includes factors like
competition, predation, disease, and other biological effects
Density Dependent Factors
Intraspecific Competition – Ecological interaction where individuals of the same species/population compete for resources in their habitat.
Density Dependent Factors
Predation - Consumption of prey by carnivores
-Regulation can occur due to preferred species of prey
Density Dependent Factors
Disease – Pathogens able to
pass from host to host in overcrowded populations with greater ease
Density Dependent Factors
Allee effect – Occurs when
population cannot survive or fails to reproduce enough to offset mortality once the population density is too low; such populations usually do not survive.
Eg. The extinct passenger pigeon.
Density Dependent Factors
Minimum viable population size – Smallest number of individual needed for a population to continue for a given period of time Small population size
can result in inbreeding and loss of genetic variation
Density Independent Factors
Factors influencing population regulation regardless of population density Human intervention – Pesticides…Climate change Environment - reproductive success based on
temperatures, natural disasters etc
Limiting Factors
Any essential resource that is in short supply or unavailable. These factors determine how much the individual or population can reproduce. Eg. light, space,
water, nutrients
Think-Pair-Share
Classify each of these as either density-dependent or density-independent. Share with a classmate – do you agree or diagree? Why? [I][C] A drought decreases the water
level of a lake, thus decreasing its carrying capacity.
Lynx prey on snowshoe hares. An increase in the snowshoe hare population caused an increase in the lynx population.
Due to the introduction of a new species of fish, a lake becomes crowded and some species do not survive.
Increased water temperature causes many aquatic organisms to die.
Why might the birth and death rates of a white-tailed deer population in the Carolinian forest of southern Ontario be a density-dependent factor?