Population Biology Notes Population Dynamics Population What is
Population Biology Notes
Population Dynamics Population What is it? A group of same species living in an area Community What is it? Collection of several different species living in an area How can 1. Size (# of individuals) populations 2. Density (# of indiv. in a certain space) change? Dispersion (clumps due to resource availability) 3. Age Distribution (# of indiv. at each age) 4. All of these = Population Dynamics (constantly changing)
Other ways a Birth + Immigration = Population increase population can change Death + Emigration = Population decrease Biotic Potential *Migration = immigration emigration _________+________ capacity for growth What does it mean? Intrinsic Rate of Increase (r) = rate of population growth if unlimited resources How can you get a high intrinsic rate? Reproduce at a very young age a. Reproduce many times b. Have many offspring at once c. Insects, sea stars, bacteria, rodents
Carrying Capacity Populations can NOT grow indefinitely due to environmental resistance What is carrying capacity? The # of individuals of a certain species that can be sustained indefinitely in a given space Figure 9 -3 Growth Factors vs. Environmental Resistance -High reprod. rate -Low reprod. rate -Generalized niche -Specialized niche -Adequate food -Inadequate food -Disease/parasite -Not disease/ resistance parasite resistant -Highly adaptable -Low adaptablity
Exponential Definition: The population is constantly multiplying Growth (ex 2, 4, 8, 16, 32, 64, 128…. ) Draw the graph of exponential growth on page 2 of your packet. J What letter of the alphabet does the curve look like? ___ J We will call this graph a “____ curve. ” (letter) Name an organism on Earth currently in exponential growth. Humans
Logistic Growth Definition: A population that has reached carrying capacity Draw the graph of logistic growth on page 2 of your packet. S What letter of the alphabet does the curve look like? ___ S We will call this graph a “_______ curve. ” (letter) What can impact carrying capacity (K)? Competition Immigration & Emigration Natural & man made catastrophes Seasonal fluctuations in resources
Definition: Density Affects population size regardless of Independent population density Factors Examples: -Natural Disasters -Unseasonable weather -Habitat destruction -Pesticide spraying Density Dependent Factors Definition: Have a greater effect on population if more dense Examples: -Predation -Parasitism -Disease -Competition for resources
1. Stable - Size fluctuates only a little above Types of or below carrying capacity (K) Population Fluctuations 2. Irruptive - Usually stable population that temporarily goes way up and then crashes back to the stable number Figure 9 -7 on page 3 Possible causes: Better weather, more food, fewer predators 3. Irregular (chaotic)Changes without any pattern (We don’t know the cause) 4. Cyclic Consistent changes of population size over a regular period of time
Predators and There are two main hypotheses: Population Size 1. Top-Down Control Predator Controls Example: -Lynx prey on snowshoe hares -Hare population goes down -Fewer hares = fewer lynx -Fewer lynx = hares increase 2. Bottom-up Control Prey Controls Example: -Hares overeat their food supply -Hare population crashes -Less hares = more plants -More plants more hares more lynx **Big predators do Top-down control (wolves, big fish, sharks, alligators…)
Reproductive Patterns 1. Asexual -One parent -Offspring are identical genetic copies Examples: Bacteria, algae, fungi, plants, some animals 2. Sexual -Two parents -Offspring are a combination of parents’ genes (½ mom, ½ dad) 97% of species reproduce this way!
Costs/Risks Sexual Reproduction -Females have to produce twice as many offspring to maintain same number (since males don’t give birth) -Chance of genetic errors/defects during splitting/recombination of chromosomes -Time consuming courtship & mating rituals -Disease transmission -Injury during mating Benefits -Greater genetic diversity in offspring (kid can be better genetically than either parent) -Males can gather food for female and offspring, can protect and train/teach young.
Opportunistic Species (r-selected species) small • Many _____ offspring • Parental care = Little/none • ______ reproductive age Early die • Most ____ before reproducing Small • ____ sized adults unstable • Adapted to _______ High climates Fluctuates • _____ population growth (above or rate below K) • Population size = Bacteria, rodents, algae, insects, annual plants Competitor Species (K-selected species) • Many _______ offspring large Very good • Parental care = • Later ______ reproductive age • Most ______ to reproduce survive • Larg ____ sized adults stable • e Adapted to _______ climates Low • _____ population growth Fairly stable rate (around K) • Population size = Large mammals, birds of prey, large & long • Examples: lived plants **PRONE TO EXTINCTION!!
Conservation What year did it start in? 1970’s Biology What is the goal? To preserve species and their ecosystems Biologists ask 3 major questions: 1. Which species is in danger of extinction? 2. What is the status of the ecosystem and what value is there to humans and other species if lost? 3. What measures can we take to help sustain ecosystems and viable populations of wild species?
population studies How do we We do ___________!! answer these 3 questions? What does this mean needs to be done? 1. Measure current population size 2. Project possible population size changes 3. Determine if existing populations are sustainable
Human Impact on Ecosystems Things we do to destroy populations: • Breaking up and damaging habitats • Simplifying ecosystems by either only planting one species or letting weeds invade • Strengthening pest species and bacteria • Eliminating some predators • Introducing exotic species • Overharvesting renewable resources
So what can we do? How can we fix this? ? ? • Realize that everything is connected to everything else (web of life) • Reduce or minimize the damage we do to nature and heal the ecological wounds we have already caused • Use sustainable methods • Take no more than we need • Preserve biodiversity of plants and animals
- Slides: 16