Ecology

INTRODUCTION TO ECOLOGY

• Ecology is the scientific study of interactions among organisms and between organisms and their physical environment.

• It explores how these interactions shape the distribution and abundance of organisms, as well as the flow of energy and cycling of matter within ecosystems.

• The ecosystem encompasses both biotic (living components, such as plants, animals, fungi, and microorganisms) and abiotic (non-living physical and chemical factors, such as sunlight, water, temperature, soil, and nutrients) components.

CHARACTERISTICS OF LIVING THINGS

1. Order: Living organisms exhibit a highly ordered and complex organization, from the molecular level (e.g., DNA, proteins) to the cellular and organismal levels.

2. Heredity/DNA: All living things possess genetic material (DNA or RNA) that carries heritable information, dictating their structure, function, and development, and passing traits to offspring.

3. Reproduction: Organisms reproduce, either sexually (involving two parents and generating genetic variation) or asexually (involving one parent and producing genetically identical offspring), ensuring the continuity of their species.

4. Growth and Development: Organisms grow by increasing in size and complexity, and develop through a programmed series of changes, guided by their genetic blueprint, to mature forms.

5. Response to the Environment: Living things react to stimuli from their environment (e.g., light, heat, touch, chemicals). This responsiveness helps them adapt and survive.

6. Evolutionary Adaptation: Over generations, populations of organisms undergo evolutionary adaptation, developing traits that enhance their survival and reproduction in specific environments through natural selection.

7. Energy Processing: All living organisms need to obtain and use energy to fuel their life processes (e.g., metabolism, growth, movement). This involves processes like photosynthesis, cellular respiration, or consuming other organisms.

8. Regulation: Organisms maintain a stable internal environment (homeostasis) despite external fluctuations, regulating factors like temperature, pH, and water balance.

LEVELS OF ORGANIZATION WITHIN THE BIOSPHERE

• The biological world can be organized into a hierarchy of increasing complexity:

  • Organism: An individual living thing.

  • Population: A group of individuals of the same species living in the same area at the same time and capable of interbreeding.

  • Community: All the different populations of species that live and interact in a particular area.

  • Ecosystem: An area of interactions among all the living (biotic) organisms in a particular area and their non-living (abiotic) physical and chemical environment.

  • Biome: Groups of ecosystems with similar climates, dominant plant forms, and animal adaptations. These are large-scale ecological units like deserts or forests.

  • Biosphere: The sum of all regions of Earth where life exists, including land, water, and atmosphere. It is the global ecological system.

• Types of Biomes (Examples):

  • Rain Forest: Characterized by high rainfall, high biodiversity, and consistent warm temperatures (e.g., Amazon).

  • Taiga (Boreal Forest): Coniferous forests found in cold northern regions, with long, cold winters and moderate precipitation.

  • Temperate Deciduous Forest: Forests with distinct seasons, experiencing warm summers and cold winters, where trees shed their leaves annually.

  • Grasslands: Dominated by grasses, with moderate rainfall and often characterized by grazing animals (e.g., savannas, prairies).

  • Desert: Arid regions with very low precipitation, extreme temperature fluctuations, and specialized drought-adapted flora and fauna.

  • Tundra: Coldest biome, characterized by permafrost, low-growing vegetation, and short growing seasons (Arctic and alpine).

ECOSYSTEMS

• Ecosystem: A community of living organisms interacting with their non-living environment.

• Components:

  • Biotic Factors: Living components, such as producers (plants, algae), consumers (animals), and decomposers (bacteria, fungi).

  • Abiotic Factors: Non-living physical and chemical components, including sunlight, water, temperature, soil pH, oxygen levels, and nutrient availability.

POPULATIONS AND COMMUNITIES

• Population: A group of interbreeding individuals of the same species living together in a defined geographical area.

  • Populations have characteristics like density, distribution, birth rates, death rates, and age structure.

  • Factors like resource availability and predation can influence population size and growth (e.g., carrying capacity).

• Community: All the interacting populations of different species that live in a particular area.

  • Community ecology studies how these species interact (e.g., competition, predation, symbiosis) and how these interactions influence community structure and biodiversity.

• Species: A group of organisms that are able to interbreed successfully in nature and produce fertile, viable offspring.

BIOLOGICAL DIVERSITY

• Biodiversity: The total variety of life on Earth, encompassing genetic diversity within species, species diversity within ecosystems, and ecosystem diversity across regions.

• High biodiversity contributes to ecosystem stability, resilience, and provides various ecosystem services vital for human well-being (e.g., food, medicine, clean water, pollination).

HABITAT AND NICHE

• Habitat: The specific physical environment or place where an organism normally lives. It provides the necessary resources and conditions for survival and reproduction (e.g., a forest for a deer, a pond for a frog).

• Niche: The unique functional role, or "address and profession," of an organism in an ecosystem. It includes all physical, chemical, and biological factors that a species needs to survive, grow, and reproduce.

  • This includes its resource requirements (e.g., food, shelter), interactions with other species (e.g., predators, prey, competitors), and its tolerance limits for various environmental conditions.

ENERGY FLOW IN ECOSYSTEMS

• Energy Flow: The transfer of energy from one trophic level to the next, tracing its path from producers through various consumers.

  • Energy enters most ecosystems from the sun and is captured by producers.

  • Energy flows directionally and is largely lost as heat at each transfer, explaining why ecosystems require a continuous influx of energy.

• Producers (Autotrophs): Organisms that make their own food, primarily through photosynthesis (using sunlight) or chemosynthesis (using chemical energy). Examples include plants, algae, and some bacteria.

• Consumers (Heterotrophs): Organisms that obtain energy by consuming other organisms.

  • Primary Consumers (Herbivores): Feed directly on producers (e.g., deer, rabbits).

  • Secondary Consumers (Carnivores/Omnivores): Feed on primary consumers (e.g., foxes eating rabbits).

  • Tertiary Consumers (Top Carnivores/Omnivores): Feed on secondary consumers (e.g., eagles eating snakes that ate rodents).

• Decomposers (Detritivores): Organisms that break down dead organic matter and waste products from all trophic levels, recycling nutrients back into the ecosystem. Examples include bacteria, fungi, and worms.

10 PERCENT RULE

• This ecological principle states that, on average, only approximately $10\%$ of the energy from one trophic level is transferred to the next trophic level.

• The remaining $90\%$ of energy is lost at each transfer due to metabolic processes (e.g., respiration, heat), incomplete consumption of biomass, and waste products.

• This significant energy loss explains why food chains are relatively short and why there is less biomass and fewer individuals at higher trophic levels.

SYMBIOSIS

• Symbiosis: Close and long-term ecological relationships between individuals of two or more different species.

  • Mutualism: A symbiotic relationship where both species directly benefit from the interaction.

  • Example: Bees pollinating flowers (bees get nectar, flowers get pollinated).

  • Parasitism: A symbiotic relationship where one species (the parasite) benefits at the expense of the other species (the host), which is harmed.

  • Example: A tick feeding on the blood of a dog (tick benefits, dog is harmed).

  • Commensalism: A symbiotic relationship where one species benefits, and the other species is neither significantly harmed nor helped.

  • Example: Barnacles attaching to whales (barnacles get a place to live and filter feed, whales are unaffected).

FOOD CHAINS AND FOOD WEBS

• Food Chain: A linear representation of the flow of energy from one trophic level to the next, illustrating who eats whom.

  • Example: Grass $\rightarrow$ Grasshopper $\rightarrow$ Frog $\rightarrow$ Snake $\rightarrow$ Hawk.

• Food Webs: A more complex and realistic diagram that illustrates multiple interconnected food chains within an ecosystem. They show how various organisms feed on and are fed upon by multiple species, reflecting the intricate network of energy flow.

TROPHIC PYRAMID

• A trophic pyramid (or ecological pyramid) is a graphical representation designed to show the biomass, energy, or number of organisms at each trophic level in an ecosystem.

• As you move up trophic levels from producers to top consumers, the amount of available energy, total biomass (except for inverted biomass pyramids in some aquatic systems), and often the number of individual organisms generally decrease.

  • Energy Pyramids: Always upright, showing the rapid decrease of energy at successive levels due to the $10\%$ rule.

  • Biomass Pyramids: Typically upright, showing the total mass of organisms at each level. Can be inverted in aquatic systems where producers (phytoplankton) have short lifespans and high turnover rates.

  • Numbers Pyramids: Shows the number of individuals at each trophic level. Can be inverted (e.g., many insects feeding on one tree).

ECOSYSTEM BALANCE

• Ecosystem stability refers to an ecosystem's ability to resist disturbance or recover quickly from it.

• Ecosystem balance can be disrupted by various factors, leading to instability or collapse.

  • Examples: Introduction of invasive species, habitat destruction, pollution (e.g., pesticide use leading to biomagnification), climate change, over-harvesting, and natural disasters.