Introduction to Ecology: Levels, Interactions, and Applications

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Introduction to Ecology

What is Ecology?

Ecology is the scientific study of the interactions between organisms and their environments. Ecologists investigate how living things interact with each other and with nonliving components of their surroundings.

Ecology: The study of relationships between organisms and their environment.
Ecologists study at multiple levels: organism, population, community, and ecosystem.

Levels of Ecological Study

Organismal Ecology: Focuses on individual organisms and their adaptations to the environment.
Population Ecology: Examines groups of individuals of the same species in a given area, focusing on factors affecting population size and growth.
Community Ecology: Studies interactions among different species living in the same area and how these affect community structure.
Ecosystem Ecology: Investigates energy flow and cycling of nutrients among living and nonliving components in an area.

Population Ecology

Population Density

Population density is the number of individuals per unit area. It is a key measure for understanding population structure and dynamics.

Population density:
Example: To estimate prairie dog density, count burrows and multiply by average number of animals per burrow.

Population Age Structure

Age structure shows the distribution of individuals among different age groups in a population. It helps predict future population growth and social needs.

Age structure diagrams (population pyramids) illustrate proportions of young, middle-aged, and older individuals.
Example: Baby booms increase demand for schools and teachers; aging populations increase pressure on healthcare and social security.

Population Age Structure Table (Mexico and U.S.)

Year	Mexico: Population Pyramid	U.S.: Population Pyramid
1990	Broad base, many young	Baby boomers highlighted
2015	More balanced	End of baby boom, more competition for jobs
2040	Projected aging	More pressure on healthcare, social security

Survivorship Curves

Survivorship curves show the number of individuals surviving at each age.

Type I: High survival in early/middle life, few offspring, much parental care (e.g., humans).
Type II: Constant death rate over lifespan (e.g., some birds).
Type III: High death rate for young, many offspring, little parental care (e.g., fish like carp).

Applications of Population Ecology

Conservation of Endangered Species: Protecting species at risk of extinction (e.g., salmon in Sonoma County).
Invasive Species: Non-native species that spread and cause harm (e.g., bullfrogs outcompeting native frogs).
Biological Control of Pests: Using one species to control another's population.
Integrated Pest Management: Combining biological, chemical, and cultural practices to reduce pests.

Community Ecology

Interspecific Interactions

Interspecific interactions are relationships between different species in a community.

Competition: Both species compete for resources (negative effect on both).
Mutualism: Both species benefit (positive effect on both).
Commensalism: One species benefits, the other is unaffected.
Predation: One species kills and eats another.
Herbivory: Animals consume plants.
Parasitism/Pathogens: One species benefits at the expense of another.

Table: Interactions Between Species in a Community

Interaction	Effect on Species 1	Effect on Species 2
Competition	-	-
Mutualism	+	+
Commensalism	+	0
Predation	+	-
Herbivory	+	-
Parasitism/Pathogens	+	-

Trophic Structure

Trophic structure describes the feeding relationships in a community, often represented as food chains or food webs.

Producers: Plants and phytoplankton that convert solar energy into chemical energy.
Primary Consumers: Herbivores and zooplankton that eat producers.
Secondary/Tertiary/Quaternary Consumers: Carnivores that eat other animals.
Food Webs: Complex networks of feeding relationships.

Biological Magnification

Biological magnification occurs when toxins become more concentrated at higher trophic levels in a food chain.

Examples of toxins: PCB, lead, mercury, DDT.
Concentration increases from producers to top consumers.

Ecosystem Ecology

Biotic and Abiotic Factors

Habitats consist of living (biotic) and nonliving (abiotic) factors that influence the distribution and abundance of organisms.

Biotic factors: Living components (other organisms).
Abiotic factors: Nonliving components (energy source, temperature, water, nutrients, wind, etc.).

Biomes

Biomes are major life zones characterized by vegetation type (terrestrial) or physical environment (aquatic).

Freshwater biomes: Lakes, rivers, wetlands; low salt concentration.
Marine biomes: Oceans, coral reefs; higher salt concentration.
Terrestrial biomes: Tropical forests, savannas, deserts, chaparral, temperate grasslands, temperate broadleaf forests, coniferous forests, tundra, polar ice.

Table: Major Terrestrial Biomes

Biome	Climate	Vegetation
Tropical Forest	Warm, high rainfall	Diverse trees
Savanna	Warm, seasonal rain	Grasses, scattered trees
Desert	Low rainfall, hot/cold	Drought-adapted plants
Chaparral	Mild, rainy winters; hot, dry summers	Fire-adapted shrubs
Temperate Grassland	Moderate rain, droughts	Grasses
Temperate Broadleaf Forest	Warm summers, cold winters	Deciduous trees
Coniferous Forest	Long snowy winters	Evergreen trees
Tundra	Bitter cold, low rain	Mosses, lichens
Polar Ice	Extreme cold	Few plants

Aquatic Zones

Photic zone: Sunlit, supports photosynthesis.
Aphotic zone: Little/no light, no photosynthesis.
Benthic realm: Bottom of aquatic biome.

Human Impact and Climate Change

Human Impact on Biomes

Deforestation increases atmospheric CO2 and reduces carbon sequestration by plants.
Freshwater depletion and pollution threaten aquatic biomes.

Climate Change

Climate change, driven by increased greenhouse gases like CO2, is altering global temperature and precipitation patterns, affecting species distributions and ecosystem health.

CO2 traps heat in the atmosphere, leading to global warming.
Effects include shifting species ranges, longer dry seasons, drought-stressed trees, and increased pest reproduction.
Populations with high genetic variability and short life spans are more likely to adapt to rapid changes.

Reducing Carbon Footprint

Actions include reducing energy use, supporting renewable energy, and conserving natural habitats.

Review Questions and Examples

Studying survival rates of finches over time is an example of population ecology.
A community consists of all organisms living in a particular area.
Carp, which produce many eggs with low survival, follow a Type III survivorship curve.
Examples of interspecific interactions:
- Bees and flowers: Mutualism
- Lichen on trees: Commensalism
- Coronavirus in humans: Parasitism/Pathogen

Additional info: Some context and definitions have been expanded for clarity and completeness.