🥀Intro to Botany Unit 5 – Plant Ecology and Ecosystems

Key Concepts and Definitions

• Plant ecology studies the interactions between plants and their environment, including abiotic factors (climate, soil) and biotic factors (other plants, animals, microbes)
• Ecosystems are complex networks of living organisms and their physical environment, linked by energy and nutrient flows
  • Consist of biotic components (plants, animals, microorganisms) and abiotic components (soil, water, air, sunlight)
• Biodiversity refers to the variety of life forms within an ecosystem, including genetic diversity, species diversity, and ecosystem diversity
• Niche is the unique role and position of a species within an ecosystem, determined by its adaptations and interactions with other species
• Habitat is the physical environment where an organism lives, providing the necessary resources and conditions for survival
• Biomes are large, distinct ecological communities characterized by similar climatic conditions, vegetation, and fauna (tropical rainforest, desert, tundra)
• Ecological succession is the gradual process of change in species composition and community structure over time, often following a disturbance

Plant Communities and Interactions

• Plant communities are assemblages of plant species that coexist in a particular area and interact with each other and their environment
• Interspecific interactions between plants include competition, facilitation, and allelopathy
  • Competition occurs when plants vie for limited resources (water, nutrients, light), leading to reduced growth and survival
  • Facilitation happens when one plant species benefits another, such as nurse plants providing shade and protection for seedlings
  • Allelopathy involves the release of chemical compounds by plants that inhibit the growth of other plants
• Mutualistic relationships between plants and other organisms, such as pollination by insects and seed dispersal by animals, are essential for reproduction and survival
• Herbivory, the consumption of plant material by animals, can significantly impact plant growth, reproduction, and community structure
• Plant-soil feedbacks occur when plants influence soil properties (nutrient availability, microbial communities), which in turn affect plant growth and community composition

Ecosystem Structure and Function

• Trophic levels describe the position of organisms within a food chain, with primary producers (plants) at the base, followed by primary consumers (herbivores), secondary consumers (carnivores), and decomposers
• Primary productivity is the rate at which plants convert solar energy into biomass through photosynthesis, forming the foundation of energy flow in ecosystems
• Decomposition is the breakdown of dead organic matter by microorganisms, releasing nutrients back into the soil for plant uptake
• Ecosystem services are the benefits provided by ecosystems to humans, such as carbon sequestration, water purification, and crop pollination
• Biodiversity plays a crucial role in maintaining ecosystem stability, resilience, and functionality
  • Higher diversity often leads to greater resistance and resilience to disturbances and environmental changes
• Keystone species have a disproportionately large impact on ecosystem structure and function relative to their abundance (sea otters in kelp forests, elephants in African savannas)
• Ecosystem engineers are organisms that modify their environment, creating and maintaining habitats for other species (beavers building dams, corals forming reefs)

Environmental Factors and Adaptations

• Abiotic factors, such as temperature, precipitation, light, and soil properties, significantly influence plant growth, distribution, and survival
• Plants have evolved various adaptations to cope with environmental stresses and optimize resource acquisition
  • Xerophytes are adapted to dry environments, with features like thick cuticles, small leaves, and deep root systems to minimize water loss and maximize water uptake (cacti, succulents)
  • Hydrophytes are adapted to aquatic environments, with traits such as air-filled tissues for buoyancy, reduced root systems, and submerged or floating leaves (water lilies, mangroves)
• Phenotypic plasticity allows plants to adjust their morphology, physiology, and behavior in response to changing environmental conditions
• Ecotypes are genetically distinct populations of a species adapted to specific environmental conditions, often resulting from local adaptation
• Photoperiodism is the physiological response of plants to the relative lengths of day and night, influencing processes such as flowering, dormancy, and germination
• Plant strategies for resource allocation include r-selection (rapid growth, high reproductive output) and K-selection (slow growth, low reproductive output, high competitive ability)

Nutrient Cycling and Energy Flow

• Nutrient cycling involves the movement of essential elements (carbon, nitrogen, phosphorus) through ecosystems, mediated by biological, geological, and chemical processes
• The carbon cycle encompasses the exchange of carbon between the atmosphere, biosphere, hydrosphere, and geosphere, with photosynthesis and respiration as key processes
  • Plants absorb atmospheric CO2 through photosynthesis, incorporating carbon into biomass
  • Respiration by plants, animals, and microorganisms releases CO2 back into the atmosphere
• The nitrogen cycle includes nitrogen fixation (conversion of atmospheric N2 to biologically available forms), nitrification, denitrification, and ammonification
  • Legumes form symbiotic relationships with nitrogen-fixing bacteria in root nodules, enhancing soil nitrogen availability
• The phosphorus cycle involves the weathering of rocks, uptake by plants, and return to the soil through decomposition and mineralization
• Energy flow through ecosystems follows the laws of thermodynamics, with energy loss at each trophic level due to heat dissipation and inefficient energy transfer
• Biomass pyramids represent the amount of organic matter at each trophic level, with primary producers forming the base and top predators at the apex

Ecological Succession and Disturbance

• Primary succession occurs on newly exposed or formed substrates (volcanic islands, glacial moraines) where no soil or vegetation previously existed
  • Pioneer species (lichens, mosses) colonize the area first, initiating soil formation and facilitating the establishment of later successional species
• Secondary succession follows a disturbance (fire, logging) that removes the existing vegetation but leaves the soil intact
  • Early successional species (grasses, herbs) quickly colonize the area, followed by shrubs and eventually trees in forest ecosystems
• Climax communities represent the final, relatively stable stage of succession, characterized by long-lived, slow-growing species and complex interactions
• Disturbances such as fires, hurricanes, and human activities can reset or alter the trajectory of succession, creating a mosaic of different successional stages across the landscape
• Intermediate disturbance hypothesis suggests that moderate levels of disturbance can maintain higher species diversity by preventing competitive exclusion and creating habitat heterogeneity
• Succession can be influenced by factors such as seed dispersal, soil properties, climate, and biotic interactions (competition, facilitation)

Human Impact on Plant Ecosystems

• Deforestation, the removal of forests for agriculture, urbanization, or resource extraction, leads to habitat loss, biodiversity decline, and altered ecosystem functions
• Habitat fragmentation divides contiguous habitats into smaller, isolated patches, reducing connectivity and increasing edge effects, which can negatively impact plant populations and communities
• Invasive species, introduced intentionally or accidentally by humans, can outcompete native species, disrupt ecosystem processes, and cause economic damage
  • Kudzu, a fast-growing vine native to Asia, has invaded many parts of the southeastern United States, smothering native vegetation and altering ecosystem structure
• Climate change, driven by anthropogenic greenhouse gas emissions, affects plant distributions, phenology, and interactions with other organisms
  • Shifting climate zones can lead to range shifts, local extinctions, and altered community composition
• Overexploitation of plant resources, such as overharvesting of medicinal plants or unsustainable logging practices, can lead to population declines and ecosystem degradation
• Urbanization and land-use change alter local environmental conditions (temperature, light, soil properties), favoring adapted plant species and homogenizing plant communities
• Pollution, including air, water, and soil contamination, can have detrimental effects on plant growth, reproduction, and ecosystem health
  • Acid rain, caused by sulfur and nitrogen oxide emissions, can acidify soils and damage plant tissues

Applications and Case Studies

• Restoration ecology applies ecological principles to restore degraded or damaged ecosystems to their natural state or a desired alternative state
  • Reforestation efforts aim to re-establish forest cover on deforested or degraded lands, providing habitat, sequestering carbon, and restoring ecosystem services
  • Prairie restoration involves reintroducing native grass and forb species, conducting prescribed burns, and managing invasive species to recreate the structure and function of tallgrass prairie ecosystems
• Agroecology integrates ecological concepts with agricultural practices to design sustainable and resilient food production systems
  • Intercropping, the practice of growing two or more crops together, can increase biodiversity, reduce pest pressure, and optimize resource use
  • Agroforestry systems combine trees with crops or livestock, providing multiple benefits such as soil conservation, carbon sequestration, and habitat for biodiversity
• Urban ecology studies the interactions between plants, animals, and the built environment in cities and towns
  • Green roofs and urban gardens can mitigate the urban heat island effect, improve air quality, and provide habitat for pollinators and other wildlife
  • Urban tree planting initiatives aim to increase tree canopy cover, providing shade, reducing stormwater runoff, and enhancing the aesthetic and recreational value of cities
• Bioremediation uses plants and their associated microorganisms to clean up contaminated soils and water
  • Phytoremediation employs plants to absorb, accumulate, or degrade pollutants such as heavy metals, pesticides, and hydrocarbons
  • Constructed wetlands harness the natural filtration capabilities of wetland plants and microbes to treat wastewater, remove nutrients, and improve water quality