Ecosystems are complex systems of living and non-living components that interact with each other. Understanding these interactions is crucial for environmental biologists to manage and protect ecosystems effectively.

Energy flows through ecosystems, starting with primary producers and moving through consumers and decomposers. Biogeochemical cycles regulate the movement of essential elements, while ecosystem productivity measures the rate of biomass production.

Components of ecosystems

• Ecosystems are complex systems composed of both living (biotic) and non-living (abiotic) components that interact with each other
• The interactions between these components shape the structure and function of the ecosystem and determine its health and stability
• Understanding the components of ecosystems is crucial for environmental biologists to effectively manage and protect these systems

Biotic factors

• Living organisms within an ecosystem (plants, animals, microorganisms)
• Play various roles such as producers, consumers, and decomposers
• Interact with each other through various relationships (competition, predation, symbiosis)
• Contribute to the flow of energy and cycling of nutrients within the ecosystem
• Examples include trees in a forest, fish in a lake, and bacteria in soil

Abiotic factors

• Non-living physical and chemical components of an ecosystem (temperature, light, water, soil, nutrients)
• Influence the distribution, abundance, and behavior of living organisms
• Can limit or support the growth and survival of biotic components
• Interact with biotic factors to create unique environmental conditions
• Examples include sunlight, precipitation, soil pH, and mineral availability

Interactions between components

• Biotic and abiotic components are interconnected and influence each other
• Interactions can be direct (predation, competition) or indirect (habitat modification)
• Positive interactions (mutualism, facilitation) benefit one or both components
• Negative interactions (competition, parasitism) harm one or both components
• The balance of these interactions maintains ecosystem stability and resilience

Energy flow in ecosystems

• Energy is the driving force behind all ecosystem processes and is essential for the survival and growth of living organisms
• In ecosystems, energy flows from the sun through a series of trophic levels, with some energy lost at each level due to inefficiencies in energy transfer
• Understanding energy flow is crucial for environmental biologists to assess the health and productivity of ecosystems

Primary producers

• Organisms that convert solar energy into chemical energy through photosynthesis (plants, algae, some bacteria)
• Form the base of the food chain and provide energy for all other organisms
• Also known as autotrophs, as they produce their own food
• Examples include phytoplankton in aquatic ecosystems and trees in terrestrial ecosystems

Consumers

• Organisms that obtain energy by consuming other organisms (herbivores, carnivores, omnivores)
• Can be classified into different trophic levels based on their position in the food chain
  • Primary consumers (herbivores) feed on primary producers
  • Secondary consumers (carnivores) feed on primary consumers
  • Tertiary consumers (top predators) feed on secondary consumers
• Examples include deer (primary consumer), wolves (secondary consumer), and humans (omnivore)

Decomposers

• Organisms that break down dead organic matter and release nutrients back into the ecosystem (bacteria, fungi)
• Play a crucial role in nutrient cycling and energy flow by making nutrients available for primary producers
• Also known as saprotrophs, as they feed on dead and decaying matter
• Examples include mushrooms, earthworms, and soil bacteria

Trophic levels

• Positions in the food chain that represent the transfer of energy from one organism to another
• Energy is lost at each trophic level due to heat, respiration, and incomplete digestion
• Typically, only about 10% of the energy is transferred from one trophic level to the next (ecological efficiency)
• The number of trophic levels in an ecosystem is limited by the amount of available energy

Food chains vs food webs

• Food chains are linear sequences that show the flow of energy from one organism to another
• Food webs are more complex networks that show the interconnected feeding relationships among organisms in an ecosystem
• Food webs provide a more realistic representation of energy flow and trophic interactions
• Examples of food chains: grass → rabbit → fox; phytoplankton → zooplankton → small fish → large fish
• Examples of food webs: a marine ecosystem with multiple interconnected species at different trophic levels

Biogeochemical cycles

• Biogeochemical cycles are the pathways through which chemical elements move through the biotic and abiotic components of an ecosystem
• These cycles are essential for the functioning of ecosystems, as they regulate the availability of nutrients and other resources for living organisms
• Understanding biogeochemical cycles helps environmental biologists assess the health of ecosystems and the impacts of human activities on these cycles

Water cycle

• The continuous movement of water through the Earth's surface, atmosphere, and underground
• Driven by solar energy and gravity, water undergoes processes such as evaporation, transpiration, condensation, precipitation, and infiltration
• Plays a crucial role in regulating climate, supporting life, and shaping landscapes
• Human activities (deforestation, urbanization, climate change) can alter the water cycle and affect water availability and quality

Carbon cycle

• The exchange of carbon between the atmosphere, biosphere, hydrosphere, and geosphere
• Carbon is a key element for life and is stored in various reservoirs (atmosphere, oceans, soil, fossil fuels)
• Processes such as photosynthesis, respiration, decomposition, and combustion drive the carbon cycle
• Human activities (fossil fuel burning, deforestation) have significantly increased atmospheric carbon dioxide levels, contributing to climate change

Nitrogen cycle

• The transformation of nitrogen between its various chemical forms (nitrogen gas, ammonia, nitrate)
• Nitrogen is an essential nutrient for plant growth and is often a limiting factor in ecosystems
• Processes such as nitrogen fixation, nitrification, denitrification, and ammonification are carried out by microorganisms
• Human activities (fertilizer use, fossil fuel burning) have altered the nitrogen cycle, leading to environmental issues such as eutrophication and acid rain

Phosphorus cycle

• The movement of phosphorus through the environment, primarily in the form of phosphate
• Phosphorus is a crucial nutrient for plant growth and is often a limiting factor in aquatic ecosystems
• The phosphorus cycle is relatively slow compared to other biogeochemical cycles, as phosphorus is not readily available in the atmosphere
• Human activities (agricultural runoff, sewage discharge) have increased phosphorus inputs into ecosystems, leading to eutrophication and algal blooms

Human impacts on cycles

• Human activities have significantly altered biogeochemical cycles, often with negative consequences for ecosystems
• Deforestation and land-use changes disrupt the water, carbon, and nitrogen cycles by altering vegetation cover and soil properties
• Fossil fuel burning and industrial activities release excess carbon dioxide and nitrogen oxides into the atmosphere, contributing to climate change and acid rain
• Agricultural practices (fertilizer use, irrigation) can lead to nutrient imbalances and water pollution
• Understanding and mitigating human impacts on biogeochemical cycles is crucial for sustainable ecosystem management

Ecosystem productivity

• Ecosystem productivity refers to the rate at which energy is converted into biomass within an ecosystem
• It is a measure of the efficiency with which ecosystems capture and utilize energy from the sun to support life
• Understanding ecosystem productivity is essential for assessing the health and sustainability of ecosystems and their ability to provide goods and services to humans

Gross vs net primary productivity

• Gross primary productivity (GPP) is the total amount of energy captured by primary producers through photosynthesis
• Net primary productivity (NPP) is the amount of energy remaining for plant growth after accounting for the energy used in respiration
• NPP represents the energy available for consumption by herbivores and other organisms in the ecosystem
• The ratio of NPP to GPP (NPP/GPP) is an indicator of the efficiency of energy utilization by primary producers

Factors affecting productivity

• Abiotic factors (light, temperature, water, nutrients) influence the rate of photosynthesis and, consequently, ecosystem productivity
• Biotic factors (species composition, diversity, interactions) also play a role in determining productivity
• Ecosystems with high biodiversity tend to have higher productivity and stability due to niche complementarity and resource partitioning
• Disturbances (natural or human-induced) can alter ecosystem productivity by changing the availability of resources and the structure of communities

Measuring productivity

• Ecosystem productivity can be measured using various methods, depending on the scale and type of ecosystem
• Direct methods involve measuring the biomass or carbon content of organisms over time
  • Harvesting and weighing plant biomass
  • Measuring tree growth using dendrometers
  • Estimating biomass using allometric equations based on plant size
• Indirect methods use proxy variables to estimate productivity
  • Measuring leaf area index (LAI) to estimate light interception and photosynthetic potential
  • Using remote sensing techniques (satellite imagery, aerial photography) to assess vegetation cover and health
  • Measuring gas exchange (carbon dioxide, oxygen) to estimate photosynthesis and respiration rates

Ecological succession

• Ecological succession is the gradual process by which ecosystems change and develop over time, following a disturbance or the formation of a new habitat
• Succession involves changes in species composition, community structure, and ecosystem functions as the ecosystem progresses towards a more stable state
• Understanding succession is crucial for environmental biologists to predict ecosystem responses to disturbances and to develop effective management strategies

Primary succession

• Occurs when a new habitat is formed (e.g., volcanic island, glacial retreat) and is colonized by pioneer species
• Begins with the establishment of simple, hardy species (lichens, mosses) that can tolerate harsh conditions
• Over time, these pioneer species modify the environment (soil formation, nutrient accumulation), making it more suitable for other species to colonize
• Succession progresses through a series of stages, with each stage characterized by a distinct community of species
• Examples include the colonization of newly formed volcanic islands and the development of plant communities on glacial moraines

Secondary succession

• Occurs when an existing ecosystem is disturbed (e.g., fire, logging, abandonment of agricultural land) and the community regenerates
• Begins with the establishment of fast-growing, opportunistic species (grasses, herbs) that can quickly colonize the disturbed area
• Succession progresses more rapidly than in primary succession, as soil and other resources are already present
• The community gradually shifts towards longer-lived, more competitive species (shrubs, trees) that can outcompete the early colonizers
• Examples include the regeneration of a forest after a wildfire and the development of a grassland on an abandoned agricultural field

Climax communities

• The final, relatively stable stage of succession, characterized by a diverse, self-sustaining community of species
• Climax communities are in equilibrium with the local environment and are resistant to minor disturbances
• The composition of climax communities is determined by the regional climate, soil conditions, and other environmental factors
• Examples of climax communities include mature forests, grasslands, and coral reefs

Examples of succession

• Yellowstone National Park, USA: Following the 1988 wildfires, the park has undergone secondary succession, with the regeneration of lodgepole pine forests and the gradual return of wildlife
• Krakatoa, Indonesia: After the volcanic eruption in 1883, the islands have undergone primary succession, with the colonization of barren rock by pioneer species and the subsequent development of diverse plant and animal communities
• Chernobyl, Ukraine: Since the nuclear accident in 1986, the abandoned area has undergone secondary succession, with the growth of forests and the return of wildlife in the absence of human intervention

Biomes

• Biomes are large, distinct ecological communities characterized by similar climate, vegetation, and animal life
• They are determined primarily by temperature, precipitation, and latitude, which influence the distribution and adaptations of species
• Understanding the characteristics and distribution of biomes is essential for environmental biologists to assess the impacts of climate change and human activities on these ecosystems

Terrestrial biomes

• Tundra: Cold, treeless regions with low-growing vegetation (mosses, lichens, sedges) adapted to harsh conditions; found in polar and alpine areas
• Taiga (boreal forest): Coniferous forests dominated by species such as spruce, fir, and pine; found in subarctic regions with long, cold winters and short, cool summers
• Temperate deciduous forest: Forests characterized by trees that lose their leaves seasonally (oak, maple, beech); found in regions with moderate temperatures and precipitation
• Temperate grassland: Grasslands with few trees, dominated by grasses and herbs; found in regions with moderate temperatures and precipitation, often maintained by fire or grazing
• Temperate rainforest: Forests characterized by high rainfall, cool temperatures, and tall, dense vegetation (redwoods, Douglas fir); found in coastal regions with oceanic climates
• Tropical rainforest: Forests characterized by high rainfall, warm temperatures, and high biodiversity; found near the equator
• Tropical savanna: Grasslands with scattered trees, characterized by a distinct wet and dry season; found in regions with warm temperatures and seasonal rainfall
• Desert: Arid regions with low precipitation and sparse vegetation adapted to drought conditions; found in areas with high temperatures and low rainfall

Aquatic biomes

• Freshwater biomes: Ecosystems characterized by low salt content, including rivers, lakes, wetlands, and streams
• Marine biomes: Ecosystems characterized by high salt content, including oceans, coral reefs, and estuaries
• Coastal biomes: Ecosystems found at the interface between land and sea, including mangroves, salt marshes, and kelp forests
• Pelagic biomes: Open ocean ecosystems, characterized by different zones based on depth and light penetration (epipelagic, mesopelagic, bathypelagic)

Characteristics of biomes

• Climate: Temperature and precipitation patterns are the primary determinants of biome distribution and characteristics
• Vegetation: The type, structure, and adaptations of plants are influenced by the climate and soil conditions of each biome
• Fauna: The diversity and adaptations of animals are closely linked to the vegetation and climate of each biome
• Soil: The properties and fertility of soils vary among biomes, depending on factors such as parent material, climate, and vegetation

Distribution of biomes

• Biomes are distributed across the Earth's surface in patterns that reflect global climate patterns and evolutionary history
• Latitude, elevation, and proximity to oceans and mountain ranges influence the distribution of biomes
• Climate change and human activities (land-use change, pollution) can alter the distribution and characteristics of biomes over time
• Understanding the factors that influence biome distribution is crucial for predicting the impacts of global change on these ecosystems

Ecosystem services

• Ecosystem services are the benefits that humans derive from ecosystems, which support human well-being and economic activities
• These services are often undervalued and not accounted for in traditional economic systems, leading to their degradation and loss
• Recognizing and valuing ecosystem services is crucial for sustainable ecosystem management and decision-making

Provisioning services

• Products obtained directly from ecosystems, such as food, water, timber, and fuel
• Examples include crops, livestock, fish, drinking water, and medicinal plants
• These services are essential for human survival and are often the most recognized and valued

Regulating services

• Benefits obtained from the regulation of ecosystem processes, such as climate regulation, water purification, and pollination
• Examples include carbon sequestration by forests, water filtration by wetlands, and crop pollination by insects
• These services maintain the stability and resilience of ecosystems and support human well-being

Cultural services

• Non-material benefits obtained from ecosystems, such as recreation, aesthetic enjoyment, and spiritual fulfillment
• Examples include ecotourism, scenic beauty, and sacred natural sites
• These services contribute to mental and physical health, social cohesion, and cultural identity

Supporting services

• Services that are necessary for the production of all other ecosystem services, such as nutrient cycling, soil formation, and primary production
• Examples include photosynthesis, decomposition, and habitat provision
• These services are often less visible and harder to quantify but are essential for the functioning of ecosystems

Value of ecosystem services

• Ecosystem services have both intrinsic and instrumental value, reflecting their inherent worth and their utility to humans
• The economic value of ecosystem services can be assessed using various methods, such as market pricing, cost-based approaches, and stated preference techniques
• Incorporating the value of ecosystem services into decision-making can help to prioritize conservation efforts and ensure the sustainable use of natural resources
• Payments for ecosystem services (PES) schemes can incentivize the protection and restoration of ecosystems by rewarding landowners and communities for their stewardship

Threats to ecosystems

• Ecosystems worldwide are facing numerous threats that jeopardize their structure, function, and ability to provide essential services to humans
• These threats are largely driven by human activities and are often interrelated, creating complex challenges for ecosystem management and conservation
• Understanding the nature and extent of these threats is crucial for developing effective strategies to protect and restore ecosystems

Habitat loss and fragmentation

• The destruction and division of natural habitats due to human land-use changes, such as urbanization, agriculture, and resource extraction
• Habitat loss reduces the available space for species, leading to population declines and local extinctions
• Fragmentation isolates populations, disrupts ecological processes, and increases the vulnerability of species to other threats
• Examples include deforestation in the Amazon rainforest and the conversion of grasslands to croplands

Invasive species

• Non-native species that are introduced to new environments and cause harm to native ecosystems and species
• Invasive species can outcompete native species, disrupt food webs, and alter ecosystem functions
• They can also cause economic damage and pose risks to human health
• Examples include the spread of kudzu in the southeastern United States and the impact of the brown tree snake on the native birds of Guam

Pollution

• The release of harmful substances into the environment, such as chemicals, plastics, and excess nutrients
• Pollution can have direct toxic effects on organisms, alter habitat quality, and disrupt ecological processes
• Examples include oil