Species, Populations, and Ecosystems

Species and Populations

• An ecosystem is a self-regulating ecological unit with interacting biotic and abiotic factors.
• Ecology studies organisms and their interactions in their environment.
• A species shares common characteristics, interbreeds, and produces fertile offspring.
• A population consists of organisms of the same species living in the same area, capable of interbreeding and producing fertile offspring.
• Abiotic factors are non-living physical factors influencing organisms and the ecosystem, including temperature, pH, salinity, sunlight, etc.
• Biotic factors are living components of an ecosystem, their interactions, and their waste, which directly or indirectly affect other organisms.
• Habitat is the environment where a species normally lives.
• A niche describes abiotic and biotic conditions and resources that a population responds to
• Fundamental niche is the full range of conditions and resources a species can survive and reproduce in.
• Realised niche is the actual conditions and resources a species exists in due to biotic interactions.
• Two species cannot occupy the same ecological niche in the same place simultaneously, and coexisting species must have slightly different needs.

Population Interactions

• Competition arises when two or more organisms require the same limited resources.
• Intra-specific competition occurs between members of the same species, resulting in stronger individuals outcompeting weaker ones as population grows.
• Inter-specific competition occurs between different species, potentially resulting in a balance where resources are shared or competitive exclusion where one species outcompetes the other.
• Predation is when a predator kills and consumes prey.
• Herbivory is when an animal (herbivore) eats a green plant.
• Parasitism where one species (the parasite) lives in or on another (the host) gaining food and shelter, usually affecting but not killing the host.
• Symbiosis is a relationship where two organisms (symbionts) live together to benefit each other.
  • Mutualism benefits all organisms involved.
  • Commensalism benefits one organism and does not affect the other.
• Carrying capacity is the maximum number of species that can be sustainably supported in a given area.
• Limiting factors slow population growth as it reaches carrying capacity, which includes the limitation of phosphates in aquatic systems, and freezing temperatures in tundra limit water availability for plants.
• Limiting factors for animals include food, water, space, mates, shelter, and temperature.
• Limiting factors for plants include water, nutrients, sunlight, carbon dioxide, space, natural calamities, and temperature.

Population Growth Curves

• S-Curve (Sigmoid Curve) starts with exponential population growth.
  • No limiting factors affect growth at first.
  • Growth gradually slows above a certain population size, resulting in a constant population size.
• J-Curve exhibits a Boom and bust pattern
  • Population grows exponentially then collapses
• Collapses are called diebacks.
• A population can exceed carrying capacity in the long term before collapsing or overshoot in the short term.

Communities and Ecosystems

• A community is a large group of interacting populations in a habitat.
• An ecosystem is a self-regulating ecological unit comprising interacting biotic and abiotic factors.
• Photosynthesis uses energy from sunlight to convert water and carbon dioxide into food.
• Leaves contain chloroplasts with chlorophyll, which splits water and combines it with carbon dioxide to make glucose.
• Green plants respire in the dark and photosynthesise/respire in the day.
• Water reaches leaves from roots through transpiration
• Respiration converts stored chemical energy (glucose) into water, carbon dioxide, kinetic energy, and heat in living cells of plants and animals.
• Food chains illustrate the flow of energy from one organism to the next.
• Arrows connect species, indicating the direction of energy flow towards the consumer.
• Producers are autotrophs that make food, needing sunlight.
  • Chemosynthetic organisms make their own food from simple compounds without sunlight, found in deep oceans.
  • Producers fix energy, provide habitats, supply nutrients, and stabilize soil.
• Consumers are heterotrophs that feed on autotrophs or other heterotrophs for energy.
  • Herbivores feed on plants.
  • Carnivores feed on animals.
  • Omnivores feed on both plants and animals. Consumers help check populations, cycle nutrients, disperse seeds, and clear dead animals
• Decomposers feed on dead and decaying matter.
  • Saprotrophs break down organic matter through extracellular digestion and absorb the products through diffusion.
  • Detritivores ingest and digest dead organic matter internally.
• Decomposers manage waste, release nutrients, and improve soil retention
• Problems of food chains are that they only show direct feeding relationships.
  • Most species have varied diet and appear in multiple food chains.
  • Some species occupy multiple trophic levels; thus, an interconnection of food chains with complex feeding relationships is called a food web.
• Ecological pyramids are graphical models of quantitative differences between living material at each trophic level.
• Their purpose is to allow easy examination of energy transfers and losses.

Types of Ecological Pyramids

• Pyramid of Numbers shows the number of organisms at each level, measuring relative numbers.
  • Easy overview/ good for comparing changes, but doesn't consider organism size or exclude immature individuals; numbers may be too large to represent.
• Pyramid of Biomass shows total dry mass of organic matter at each trophic level.
  • Biomass in grams/m² or joules/m².
• Biomass is not related to size, can be inaccurate, does not account for organism age, but counts all individuals
• Pyramid of Productivity shows the rate of energy flow or biomass through trophic levels, showing energy/biomass available.
  • Most accurate, allows for ecosystem comparison, but cannot invert and is hard to collect data for over time.

Flows of Energy and Matter

• Energy from solar radiation is the main driver.
• Solar radiation includes visible light and invisible wavelengths for ultraviolet/infrared, where most solar radiation is absorbed and ultraviolet light is absorbed by ozone.
• Ultraviolet/visible light changes to heat energy and most energy reflects.
• Some energy heats the land.
• Plants use only 1-4% of incoming energy, converting it to chemical energy.
• Productivity is the rate of energy conversion into biomass.
• Gross productivity is total gain in energy or biomass.
• Net productivity is the remaining gain in energy or biomass after respiration.
  • GPP is the total energy/biomass gain of green plants (photosynthesis).
  • NPP is green plant energy/biomass gain after respiration, representing potentially available biomass consumers eat.
    • NPP = GPP – R (respiration)
• Gross secondary productivity(GSP) is consumer energy/biomass uptake.
  • GSP = food eaten – fecal loss
• Net secondary productivity (NSP) is consumer energy or biomass gain after losses to respiration.
• NSP = GSP – R
• Energy flows one way, from solar radiation to heat loss.
• Bioaccumulation is the build-up of undegradable pollutants within an organism/trophic level.
• Biomagnification is increased concentration of pollutants.
  • Toxins like DDT accumulate due to decreased biomass/ energy.

Carbon Cycle

• Chemical nutrients in the biosphere cycle through absorption by organisms, circulation through trophic levels, and release back into the atmosphere.

Carbon Cycle Storages

• Organic - complex carbon molecules.
• Organisms (biomass), fossilised life forms (fossil fuels)
• Inorganic - simple carbon molecules.
• rocks and fossils, oceans/water bodies, soil, and atmosphere.

Carbon Cycle Flows

• Transfers occur from feeding on plants/ dead organisms and from carbon dioxide dissolving in rainwater/oceans.
• Transformations: Photosynthesis is the transformation of (carbon dioxide into glucose).
• Respiration and combustion transform organic matter into carbon dioxide.
• Incomplete decomposition and fossilisation transform organic matter into oil and coal.

Nitrogen Cycle

• Nitrogen fixation converts atmospheric nitrogen into usable forms for plants, and bacteria in soil or Cyanobacteria/algae or Lightening preforms conversions too.
• Nitrification converts ammonium into nitrites/nitrates absorbed by plants.
• Denitrification converts ammonium, nitrates, and nitrites into nitrogen gas released into the atmosphere, and occurs in waterlogged or low-oxygen conditions.

Human Impacts

• Combustion increases oxides of carbon and nitrogen.
• Deforestation and agriculture releases carbon dioxide/nitrous oxides which results in the acidification, loss of nitrogen stores and soil erosion.
• Pesticides/Herbicides reduce store of carbon and nitrogen.
• Extracting oil only reduces carbon stores.

Biomes, Zonation and Succession

• Biome is ecosystems sharing climatic conditions/community types across continents/national borders.
• Biosphere the part of the Earth where life exists.

Types of biomes

• Aquatic, marine, desert, forest, grasslands and tundra.

Location

• Latitude closer to equator more warmer.
• Altitude higher altitudes have lower temperatures
• Ocean currents.

Tropical Rainforest

• Location: between 5N and 5S
• Weather: +200cm/year rainfall, +26 degrees, high humidity.
• Biodiversity: 5 layers, emergents, epiphytes, fan palms.
• Adaptations: leaves for sunlight, buttress roots, nocturnal, drip tips.
• Activity: Farming, deforestation due to pastoral and logging.

Deserts

• Location: 30N/S
• Weather: Limited waster, +250mm/year rainfall, very hot and very cold.
• Biodiversity: Store water in the form of waxy leaves.
• Adaptations: short life span.
• Human impact: Salinisation of soil, cereal crops.

Temperate Grasslands

• Location: 40-60N/S equator:
• Weather: High temperature, moderate/ low rainfall with low temperatures.
• Biodiversity: High nutrient content
• Adaptation: Burrowing
• Human impact: Overgrazing.

Temperate Forests

• Location 40-60N
• Weather: Middle temp, cold Winters, rainfall annually and humidity.
• Biodiversity: Big roots in soil, leaves, quick cycling.

Arctic Tundra

• Temperature: Low, wind, freezing
• biodiversity; Plants store water
• Adaptation: Prevent growth
• Human activity: Mining/ Oil and gas, fragile damages.

Succession

• Succession is a orderly change where by the beginning begins simple and the climax is complex

Sucession stages

• Bare and inorganic Surface
• Colonisation
• Establishment
• Compition.
• Stabilisation
• Climax community

Types of ecological Sucession

• Primary starts with a bare inorganic surface with no soil
• Secondary regenerates soil.

Primary

• Very Long cycle
• None humus
• The pioneer are brought in animals

Zonation

• Change based on the gradient of the environments.
• Altitude, Shorecover

Change with Sucession

• Hostipable and complex community in the end.
• High content with stability.
• Productivity is better.

Investigating Ecosystems: Practical Work

(Note: A short range of important methods are mentioned here which were taught at my school and are tested more often. However, there are others in the syllabus and in textbooks, so do go through these to get a complete perspective on this chapter and on methods to use for your internal assessment.) • QUADRATS ○ A quadrat is a frame of a specific size which may be divided into subsections. They may be of 1m², 10m², etc. ○ The size of the quadrat is chosen depending on the size of the organisms being sampled. ○ How to place quadrats: Π Random quadrats can be placed by throwing them on the ground – however, this can be dangerous and may not actually be random. Conventionally, the area of study is mapped and a grid is drawn over it. Each square of the grid in numbered, and a random number table is used to identify which squares (i.e. regions of the area of study) will be sampled. After this is done, reach the area of study and go to the squares marked in your map. Count the number of species (if possible) or estimate how many squares of the quadrat are filled up by the species. Record this number and repeat the process at the other chosen locations in the area of study. Tabulate the data and take an average of it. IF AREA IS USED: estimate the area of one square of the quadrat and multiply it by the number of squares covered by the species. For half covered squares, multiply the number by 2, for one-fourth covered, multiply by 4. • Repeat this at other sites and find the average area covered. TRANSECTS ○ A transect is a sample path/line/strip along which one records the occurrence and/or distribution of plants and animals in a particular study area. ○ Continuous and systematic sampling is conducted along transects.