🐇Honors Biology Unit 17 – Ecology – Interactions in the Biosphere

Key Concepts and Definitions

• Ecology studies the interactions between organisms and their environment (biotic and abiotic factors)
• Biotic factors include living components of an ecosystem such as plants, animals, and microorganisms
• Abiotic factors consist of non-living components like temperature, light, water, and soil
• Habitat refers to the physical environment where an organism lives and includes both biotic and abiotic factors
• Niche describes an organism's role within its ecosystem including its habitat, interactions with other species, and resource use
• Biodiversity encompasses the variety of life at all levels of organization from genes to ecosystems
• Ecosystem services are benefits provided by ecosystems to humans (clean air, water purification, pollination)

Levels of Ecological Organization

• Organisms are individual living entities that belong to a species
• Populations consist of individuals of the same species living in a specific area at the same time
  • Population density measures the number of individuals per unit area or volume
  • Population distribution describes how individuals are spread out within their habitat (clumped, uniform, random)
• Communities include all the populations of different species living and interacting in a particular area
• Ecosystems encompass both the biotic communities and abiotic factors in a given area and their interactions
• Biomes are large regions characterized by similar climate, vegetation, and animal life (tropical rainforest, tundra, desert)
• The biosphere is the portion of Earth that supports life including the atmosphere, hydrosphere, and lithosphere

Types of Species Interactions

• Competition occurs when two or more species use the same limited resources leading to reduced fitness for both
  • Intraspecific competition happens between individuals of the same species
  • Interspecific competition takes place between individuals of different species
• Predation is an interaction where one organism (predator) hunts, kills, and consumes another organism (prey)
• Herbivory involves an animal (herbivore) feeding on plants or algae
• Parasitism is a relationship where one organism (parasite) lives on or inside another organism (host) causing harm
• Mutualism benefits both species involved in the interaction (pollination, nitrogen fixation in legumes)
• Commensalism is an interaction where one species benefits while the other is unaffected (barnacles on whales)

Energy Flow in Ecosystems

• Primary producers convert light energy into chemical energy through photosynthesis (plants, algae, cyanobacteria)
• Consumers obtain energy by eating other organisms and can be classified as herbivores, carnivores, or omnivores
  • Primary consumers are herbivores that eat primary producers
  • Secondary consumers are carnivores that eat primary consumers
  • Tertiary consumers are carnivores that eat secondary consumers
• Decomposers break down dead organisms and waste products releasing nutrients back into the ecosystem (bacteria, fungi)
• Food chains show the linear transfer of energy from one trophic level to the next (producer → primary consumer → secondary consumer)
• Food webs illustrate the complex interconnections between multiple food chains in an ecosystem

Nutrient Cycling

• Biogeochemical cycles describe the movement of essential nutrients through the biosphere (carbon, nitrogen, phosphorus, water)
• The carbon cycle involves the exchange of carbon between the atmosphere, oceans, and living organisms through processes like photosynthesis and respiration
• The nitrogen cycle includes nitrogen fixation by bacteria, uptake by plants, and return to the atmosphere through denitrification
• The phosphorus cycle is sedimentary with phosphorus moving from rocks to soil to living organisms and back to sediments
• The water cycle (hydrologic cycle) encompasses evaporation, transpiration, condensation, precipitation, and runoff

Population Dynamics

• Population growth is influenced by birth rates, death rates, immigration, and emigration
• Exponential growth occurs when a population increases at a constant rate resulting in a J-shaped curve
• Logistic growth happens when a population's growth slows as it approaches the carrying capacity (K) producing an S-shaped curve
• Carrying capacity is the maximum population size an environment can sustain given available resources
• Density-dependent factors affect population growth rates based on population density (competition, predation, disease)
• Density-independent factors impact populations regardless of their density (natural disasters, climate change)

Community Ecology

• Species diversity refers to the number of different species in a community (species richness) and their relative abundances (species evenness)
• Ecological succession is the gradual process of change in species composition over time
  • Primary succession begins in a newly formed, uninhabited area (lava flows, glacial retreat)
  • Secondary succession occurs in a previously inhabited area following a disturbance (wildfire, abandoned farmland)
• Pioneer species are the first to colonize a disturbed or newly formed area (lichens, grasses)
• Climax communities are the final, stable stage of succession with long-lived species (mature forests)
• Keystone species have a disproportionately large impact on their ecosystem relative to their abundance (sea otters, wolves)
• Foundation species create and maintain habitats that support many other species (corals, kelp, trees)

Human Impact on Ecosystems

• Habitat destruction is the primary cause of biodiversity loss and can result from deforestation, urbanization, and agriculture
• Invasive species are non-native organisms that cause ecological or economic harm in a new environment (zebra mussels, kudzu)
• Overexploitation occurs when a resource is consumed at a rate exceeding its ability to regenerate (overfishing, poaching)
• Pollution can disrupt ecosystems through the introduction of harmful substances (pesticides, plastic waste, oil spills)
  • Bioaccumulation is the buildup of toxins in an organism over time
  • Biomagnification is the increasing concentration of toxins at higher trophic levels
• Climate change driven by human activities (fossil fuel combustion, deforestation) alters temperature, precipitation, and ocean chemistry
• Conservation efforts aim to protect and restore ecosystems through strategies like habitat preservation, species reintroduction, and sustainable resource management