🔬General Biology I Unit 44 – Ecology and the Biosphere

Key Concepts and Definitions

• Ecology studies the interactions between organisms and their environment at various levels of organization
• The biosphere encompasses all living organisms on Earth and the environments they inhabit
• Ecosystems consist of a community of organisms interacting with each other and their abiotic environment
• Habitat refers to the physical location where an organism lives and includes both biotic and abiotic factors
• Niche describes an organism's role within its ecosystem, including its interactions with other organisms and its use of resources
• Biodiversity encompasses the variety of life at all levels, from genes to ecosystems, and plays a crucial role in maintaining ecosystem stability and resilience
• Ecological succession is the gradual process by which ecosystems change over time, often following a disturbance, and can be primary (starting with bare rock) or secondary (starting with soil)

Levels of Ecological Organization

• Organisms are individual living entities that belong to a species and interact with their environment to survive and reproduce
• Populations consist of individuals of the same species living in a specific area at a given time
• Communities are assemblages of multiple populations of different species that interact with each other within a shared environment
• Ecosystems encompass both the biotic communities and the abiotic factors (such as soil, water, and sunlight) with which they interact
• Biomes are large, distinct regions of the Earth characterized by similar climate, flora, and fauna (tropical rainforest, tundra)
• The biosphere is the global sum of all ecosystems, encompassing all living organisms and their environments on Earth

Biotic and Abiotic Factors

• Biotic factors are the living components of an ecosystem, including all organisms (plants, animals, fungi, microbes)
• Abiotic factors are the non-living components of an ecosystem that influence the survival and growth of organisms
  • Examples of abiotic factors include temperature, light, water, soil, and atmospheric gases
• The interactions between biotic and abiotic factors shape the structure and function of ecosystems
• Organisms adapt to the specific biotic and abiotic factors in their environment through the process of natural selection
• Changes in abiotic factors (climate change, pollution) can have significant impacts on the biotic components of an ecosystem
  • For example, rising temperatures due to climate change can alter the distribution and survival of plant and animal species

Energy Flow in Ecosystems

• Energy enters most ecosystems as sunlight, which is captured by primary producers (plants) through photosynthesis
• Primary producers convert light energy into chemical energy stored in organic compounds, forming the base of the food web
• Consumers obtain energy by eating other organisms, and can be classified as primary (herbivores), secondary (carnivores that eat herbivores), or tertiary (carnivores that eat other carnivores)
• Decomposers (bacteria, fungi) break down dead organisms and waste products, releasing nutrients back into the ecosystem
• Energy is lost at each trophic level due to metabolic processes, limiting the number of trophic levels in an ecosystem (typically 4-5)
• The amount of energy available at each trophic level can be represented by an ecological pyramid, with primary producers forming the base and top predators at the apex

Biogeochemical Cycles

• Biogeochemical cycles describe the movement of essential elements (carbon, nitrogen, phosphorus) through the biotic and abiotic components of ecosystems
• The carbon cycle involves the exchange of carbon between the atmosphere, oceans, and living organisms through processes such as photosynthesis, respiration, and decomposition
  • Human activities (fossil fuel combustion, deforestation) have significantly altered the carbon cycle, leading to increased atmospheric CO2 levels and climate change
• The nitrogen cycle includes the processes of nitrogen fixation (conversion of atmospheric N2 to usable forms), nitrification, denitrification, and ammonification
  • Bacteria play a crucial role in the nitrogen cycle by fixing atmospheric nitrogen and converting it into forms usable by plants
• The phosphorus cycle involves the movement of phosphorus from rocks and sediments to living organisms and back, with no significant atmospheric component
• Water cycles through ecosystems via the processes of evaporation, transpiration, condensation, and precipitation

Population Dynamics

• Population size refers to the number of individuals of a species in a given area at a specific time
• Population density is the number of individuals per unit area or volume
• Populations can exhibit exponential growth when resources are abundant, but are ultimately limited by carrying capacity (the maximum population size an environment can sustain)
• Factors that influence population growth include birth rates, death rates, immigration, and emigration
• Populations are regulated by density-dependent factors (competition, predation) and density-independent factors (natural disasters, climate)
• Age structure diagrams represent the distribution of individuals among different age groups in a population and can provide insights into its growth potential

Community Interactions

• Predation occurs when one organism (the predator) consumes another (the prey), transferring energy up the food chain
• Competition arises when two or more species vie for limited resources, such as food, water, or space
  • Intraspecific competition occurs between individuals of the same species, while interspecific competition occurs between different species
• Symbiosis is a close, long-term interaction between two species, which can be mutualistic (both species benefit), commensalistic (one benefits while the other is unaffected), or parasitic (one benefits at the expense of the other)
• Herbivory is a form of predation in which animals consume plants, and can have significant impacts on plant community structure and ecosystem function
• Keystone species have disproportionately large effects on their ecosystems relative to their abundance (sea otters in kelp forests)

Biomes and Aquatic Ecosystems

• Terrestrial biomes are characterized by distinct climate patterns and vegetation types, and include tropical rainforests, temperate forests, grasslands, deserts, and tundra
• Aquatic ecosystems are classified based on their salinity, depth, and water flow, and include freshwater (lakes, rivers, wetlands) and marine (oceans, estuaries, coral reefs) environments
• The distribution of biomes is primarily determined by temperature and precipitation patterns, which influence the types of vegetation that can grow in a given area
• Biomes and aquatic ecosystems are home to unique assemblages of species that are adapted to the specific conditions of their environment
• Ecotones are transitional areas between adjacent biomes or ecosystems, and often exhibit high levels of biodiversity
• Climate change and human activities (habitat destruction, pollution) pose significant threats to the integrity and functioning of biomes and aquatic ecosystems worldwide

Human Impact on the Biosphere

• Habitat destruction, fragmentation, and degradation are major drivers of biodiversity loss, as they reduce the availability of suitable living spaces for species
• Overexploitation of natural resources (overfishing, deforestation) can disrupt ecosystem balance and lead to the decline or extinction of species
• Pollution (air, water, soil) can have detrimental effects on the health of organisms and the functioning of ecosystems
  • Examples include acid rain, eutrophication of water bodies, and the accumulation of plastic waste in marine environments
• Climate change, largely driven by human activities such as fossil fuel combustion and deforestation, is altering temperature and precipitation patterns worldwide, with far-reaching consequences for biodiversity and ecosystem functioning
• Invasive species, often introduced by human activities (international trade, pet trade), can outcompete native species and disrupt ecosystem balance
• Conservation efforts, such as habitat protection, sustainable resource management, and restoration projects, are crucial for mitigating the negative impacts of human activities on the biosphere