Unit 3 - Populations PDF

Unit 3 - Populations Enduring Understanding: Populations change over time in reaction to a variety of factors 3.4 Carrying Capacity Objectives, EKs, and Skills ...

Unit 3 - Populations Enduring Understanding: Populations change over time in reaction to a variety of factors 3.4 Carrying Capacity Objectives, EKs, and Skills  ★ Fig. 1 is theoretical ★ Fig. 2 is more realistic ★ Pop. briefly “overshoots” (K) and then die-off happens Fig. 1 Fig. 2 Carrying Capacity (K): the max. Number of individuals in a pop. that an ecosystem can support (based on limiting resources) Carrying Capacity (K) ▰ Die-off: sharp decrease in pop. size ▰ Highest pop. size an ecosystem can support when resource depletion (overshoot) based on limiting resources: leads to many individuals dying ▻ Food ▻ Ex: many deer starve with too many ▻ Water new young deer feeding in spring ▻ Habitat (nesting sites, space) ▰ Overshoot: when a population briefly exceeds carrying capacity ▻ Ex: deer breed in the fall, give birth all at once in spring; sudden spike in pop. = overshoot ▰ Consequence of overshoot: resource depletion ex: overgrazing in deer Die-off Example ▰ Reindeer of St. Paul Island ▻ 25 introduced in 1910 ▻ Growth was gradual (10’-30’), then exponential (30’-37’) ▻ Carrying capacity was overshot ▻ Sharp die-off lead to population crash as food resource (lichen) were severely depleted ▰ Real pops. don’t always fluctuate around carrying capacity. If resource depletion is severe enough, total pop. crash can occur Predator-Prey 1. Hare pop. increase due to low predator pop. (lynx) 2. Lynx pop. increase due to increase in food (hare) 3. Increasing lynx pop. limits hare pop; leads to die-off 4. Hare die-off decreases lynx food source, leading to die-off 5. Hare pop. increase due to low predator pop. (lynx) FRQ Practice 3.4 Explain the impact that the canine virus had on the moose population based on the graph. 3.5 Pop. Growth & Resource Availability Objectives, EKs, and Skills  Population Characteristics ▰ Size (N): total # of individuals in a given area at a given time ▻ Larger = safer from population decline ▰ Density: # of individuals/area ▻ Ex: (12 panthers/km2) ▻ High density = higher competition, possibility for disease outbreak, possibility of depleting food source ▰ Distribution: how individuals in population are spaced out compared to each other ▻ Random (trees) ▻ Uniform (territorial animals) ▻ Clumped (herd/group animals)  Pop. Characteristics & Growth Factors ▰ Sex Ratio: ratio of males to females. Closer to 50:50, the more ideal for breeding (usually) ▻ Die-off or bottleneck effect can lead to skewed sex ratio (not enough females) ▰ Density-Independent Factors: factors that limiting pop. growth influence population growth independent of their size ▰ Density-Dependent Factors: factors that ▻ Ex: natural disasters (flood, hurricane, influence population growth based on size: tornado, fire) ▻ Ex: food, competition for habitat, water, ▻ It doesn’t matter how big or small a light, even disease pop. is, natural disasters limit them ▻ All of these things limit pop. growth based both on their size; aka - small pop. don’t experience these, large do Ex. of Density-Dependent Factor ▰ Food is a density dependent factor. (also a limiting resource) ▻ When twice as much food was added to the dish, both species increased carrying capacity by about 2x  Biotic potential = exponential growth Logistic growth = initial rapid growth, then limiting factors limit pop. to K ▰ Biotic Potential = maximum potential growth rate, with no limiting resources ▻ May occur initially, but limiting resources (competition, food, disease, predators) slow growth, & eventually limit pop. to carrying capacity (K)  Calculating Population Change ▰ Population Size = (Immigrations + births) - (immigrations + deaths) ▻ Ex: An elk pop. of 52 elk has 19 births and 6 deaths in a season, and 5 new elk immigrate to the herd and 0 elk emigrate from the herd (19+5) - (6+0) = +18 elk 52 + 18 = 70 elk 15  FRQ Practice 3.5 Calculate the percent change in the population size of a 14 wolf pack that experiences 5 deaths, 3 births, and 4 new wolves released into the pack from a nearby wildlife sanctuary.