Unit 3.4-3.5 Population Growth & Resource PPT PDF

3.4 Carrying Capacity Objectives, EKs, and Skills  ★ Fig. 1 is theoretical ★ Fig. 2 is more...

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) 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 pop. 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) 3.5 Pop. Growth & Resource Availability Objectives, EKs, and Skills Factors that Regulate Population Abundance and Distribution Population size- the total number of individuals within a defined area at a given time. Population density- the number of individuals per unit area at a given time. Population distribution- how individuals are distributed with respect to one another. Population sex ratio- the ratio of males to females Population age structure- how many individuals fit into particular age categories.  Pop. Characteristics ▰ Size (N): total # of individuals in a given area at a given time ▻ Larger = safer from pop. 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 pop. are spaced out compared to each other ▻ Random (trees) ▻ Uniform (territorial animals) ▻ Clumped (herd/group animals)  Metapopulations Metapopulations- a group of spatially distinct populations that are connected by occasional movements of individuals between them.  Exponential Growth Model Growth rate- the number of offspring an individual can produce in a given time period, minus the deaths of the individual or offspring during the same period. Intrinsic growth rate- under ideal conditions, with unlimited resources, the maximum potential for growth.  Exponential Growth Model J-shaped curve- when graphed the exponential growth model looks like this.  Logistic Growth Model Logistic growth- when a population whose growth is initially exponential, but slows as the population approaches the carrying capacity. S-shaped curve- when graphed the logistic growth model produces an “S”. Variations of the Logistic Model If food becomes scarce, the population will experience an overshoot by becoming larger than the spring carrying capacity and will result in a die-off, or population crash.  Biotic potential = exponential growth Logistic growth = initial rapid growth, then limiting factors limit pop. to K ▰ Biotic Potential = max. 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)  Pop. Characteristics & Growth ▰ Factors Sex Ratio: ratio of males to females. Closer to 50:50, the more ideal for ▰ Density-Independent breeding (usually) Factors: factors that ▻ Die-off or bottleneck effect can lead to skewed sex ratio (not enough influence pop. growth females) limiting pop. growth independent of their size ▻ Ex: natural disasters ▰ Density-Dependent Factors: factors that influence pop. growth based on (flood, hurricane, size: tornado, fire) ▻ Ex: food, competition for habitat, ▻ It doesn’t matter how water, light, even disease ▻ All of these things limit pop. growth big or small a pop. is, based on their size; aka - small pop. natural disasters limit don’t experience these, large do them both 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  Calculating Population Change 19 ▰ 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 heart (19+5) - (6+0) = + 18 elk 52 + 18 = 70 elk  Practice What You Know 1. Population distribution is a. often clumped in response to predation b. used by wildlife managers when regulating hunting and fishing c. measured relative to other species d. uniform in most tree species e. important when estimating the number of offspring expected 2. What is true about a population’s carrying capacity? a. It is denoted as C. b. It is usually used when studying ecosystems c. It depends on a limiting resource d. It is controlled by density independent factors e. The population of a species cannot exceed it.  Practice what you know 3. The intrinsic growth of a population a. occurs at the population’s carrying capacity b. depends on the limiting resources of the population c. increases as the population size increases d. only occurs under ideal conditions e. decreases as the population size increases