Welcome to Class! 9-14 and 9-15 Complete the following: Pick two different biomes, discuss how are their biotic and abiotic factors different in your journal New entry “Population Grow and Limiting Factors” Check A-Day Students Foodweb and Bean Pyramids Go to restroom? Define a vocabulary before go Tutoring hours: Wednesdays afterschool 4-5pm Mondays, Wednesdays, Fridays morning 7:30am Agenda Lecture notes on Population and limiting factor Concept Maps Online Population Growth Lab Homefun: Study for your Test Next Friday 9-18 is our Unit One Test!!! Study! How Populations Grow Learning Objectives Describe how ecologists study populations. Identify factors that affect population growth. Describe exponential growth. Describe logistic growth. Describing Populations • Geographic range • Density and distribution • Growth rate • Age structure Geographic Range Density and Distribution Growth Rate Growth rate = 0 Population size is unchanged. Growth rate > 0 Population size is growing. Growth rate < 0 Population size is decreasing. Bacterial population Age Structure • Only certain age groups can reproduce. • Only females produce offspring. Population Growth Births Deaths Immigration Emigration Exponential Growth Under ideal conditions with unlimited resources, a population will grow exponentially. Population is rapidly increasing. Logistic Growth When a population’s growth slows and then stops, following a period of exponential growth Phase II Phase III Phase I Carrying Capacity The maximum number of individuals of a particular species that a particular environment can support Population stabilizes at carrying capacity. Overview: How Populations Grow 1. “Ten individual per square hectare” is a description of population . density 2, When resources are limited, a population will grow logistically . 3. When growth rate is greater than zero , the population is growing. Limits to Growth Learning Objectives Identify factors that determine carrying capacity. Identify the limiting factors that depend on population density. Identify the limiting factors that do not depend on population density. Limiting Factors Limiting factors determine the carrying capacity of an environment for a species. Density dependent Density independent Density-Dependent Factors Density-dependent limiting factors operate strongly when population density reaches a certain level. Competition • More individuals use up resources sooner. • Individuals may compete for food, water, space, sunlight, shelter, mates, territories. Predator–Prey Relationships Herbivore Effects Populations of herbivores and plants cycle up and down like populations of predators and prey. Parasitism and Disease • Parasites and diseases can spread quickly through dense host populations. • Stress from overcrowding can lead to lower birth rates, higher death rates, and higher emigration rates. Density-Independent Factors Density-independent limiting factors affect all populations regardless of population size and density. Density-Independent Factors • Examples: hurricanes, droughts, floods, wildfires • Density-independent factors may actually vary with population density. Canyon Lake, TX Controlling Invasive Species Density-independent measures? • Herbicides, mechanical removal Density-dependent measures? • Predation Salvinia Expensive, temporary Another invasive species? Overview: Limits to Growth Flood waters cover a field of wildflowers. Density dependent Non-native snakes released into a wetland prey on native rodents. Density independent Flu virus spreads quickly in schools. Wildfires spread through a grassland.