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Chapters 3-5 Biology – Miller • Levine

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1 Chapters 3-5 Biology – Miller • Levine
Ecology Chapters 3-5 Biology – Miller • Levine

2 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)

3 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

4 Levels of Organization

5 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

6 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

7 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

8 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

9 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

10 Ecological Pyramids

11 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

12 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

13 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)

14 Symbiosis

15 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

16 Exponential Growth Under ideal conditions with unlimited resources, a population will grow exponentially J-shaped curve

17 Logistic Growth As resources become less available, the growth of a population slows or stops S-shaped curve

18 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

19 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

20 Density-Dependent Factors
Predation – when one species feeds on another Predator – the organism that feeds on the prey Prey – the organism being eaten

21 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

22 Evolution of Populations
Directional selection - form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve

23 Evolution of Populations
Stabilizing selection - form of natural selection by which the center of the curve remains in its current position; occurs when individuals near the center of a distribution curve have higher fitness than individuals at either end

24 Evolution of Populations
Disruptive selection - form of natural selection in which a single curve splits into two; occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle

25 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

26 Survivorship Curves

27 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

28 Primary Succession

29 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 Ex. Mt. St. Helens

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