Ecology Chapters 3-5 Biology – Miller • Levine What is Ecology? • The scientific study of: – Interactions among organisms – Interactions between organisms and their environment • Biosphere – portions of the Earth where life exists (land, water, and air) Levels of Organization • Species – group of organisms that can breed and produce fertile offspring • Population – a group of individuals of the same species that live in the same area • Community – different populations that live in the same area • Ecosystem – all the organisms plus the nonliving environment • Biome – group of ecosystems with the same climate and similar communities Levels of Organization Energy Flow • Sunlight is the main energy source for life on Earth. • Autotrophs (producers) – organisms that make their own food – Photosynthesis – use light energy to make food – Chemosynthesis – use chemical energy to make food Energy Flow • Heterotrophs (consumers) – organisms that must feed on other organisms for energy – Herbivores – eat only plants – Carnivores – eat other animals – Omnivores – eat both plants and animals – Detrivores – feed on dead matter – Decomposers – break down organic matter Feeding Relationships • Energy flows through an ecosystem in one direction (sun → producers → consumers) • Food chain – a series of steps in which organisms transfer energy by eating and being eaten Feeding Relationships • Food web – a network of complex feeding interactions • Trophic levels – each step in a food chain or food web – 1st – producers – 2nd – primary consumers – 3rd – secondary consumers – 4th – tertiary consumers Ecological Pyramids • Energy Pyramid – shows the amount of energy available at each trophic level – Only about 10% of the energy is transferred to the next level • Biomass Pyramid – shows the amount of living tissue within each trophic level • Pyramid of numbers – shows the number of organisms at each trophic level Ecological Pyramids Biotic and Abiotic Factors • Biotic factors – the living things that influence organisms • Abiotic factors – the nonliving things that influence organisms – Light – Soil – Wind – Water – Temperature Habitat and Niche • Habitat – the area where an organism lives • Niche – the role an organism plays in its habitat – No two species can share the same niche in the same habitat Community Interactions • Symbiosis – any relationship in which two species live closely together – Mutualism – both species benefit (flowers & insects) – Commensalism – one species benefits while the other is neither helped nor harmed (orchids in a rainforest) – Parasitism – one organism benefits while the other is harmed (fleas on a dog) Symbiosis Ecological Succession • The series of changes that occurs in a community over time • Primary succession – occurs on surfaces where no soil exists (no previous life) – Pioneer species – the first species to populate the area – Lichens → mosses → grasses → shrubs → trees Primary Succession Ecological Succession • Secondary Succession – when a disturbance changes the existing community without removing the soil – Tornadoes, fire, clear cutting – Occurs much quicker than primary succession – Climax community – the relatively stable final community Populations • Population density – the number of individuals per unit area • Population growth – increase in size of a population • Population size can be affected by: – Number of births – Number of deaths – Immigration – organisms moving into an area – Emigration – organisms moving out of an area Exponential Growth • Under ideal conditions with unlimited resources, a population will grow exponentially • J-shaped curve Logistic Growth • As resources become less available, the growth of a population slows or stops • S-shaped curve Limiting Factors • A factor that causes population growth to decrease • The population size will usually remain constant • Creates the s-shaped curve • Two kinds of limiting factors: – Density-dependent – Density-independent Density-Dependent Factors • A limiting factor that depends on population size • Competition – organisms compete for resources – Between members of the same species – Between members of different species • Parasitism and disease Density-Dependent Factors • Predation – when one species feeds on another – Predator – the organism that feeds on the prey – Prey – the organism being eaten Density-Independent Factors • Affects all populations, regardless of the population size • Unusual weather – heavy storms • Natural disasters – tornado, volcanic eruption • Seasonal cycles – insects die during winter • Human activities – clear-cutting forests Human Population Growth • At first the human population grew slowly • About 500 years ago it started increasing rapidly • Resembles the J-shaped curve US & World Populations