C.1 Species and Communities Limiting factors

● Limiting factors are factors lacking for certain organisms Plant distribution affected by: Animal distribution affected by:

-Temperature -Water availability -Light intensity -Soil pH -Soil salinity -Mineral nutrient availability

-Temperature -Water -Breeding sites -Food supply -Territory

● Examples ○ Tigers

■ Tigers require large territories ■ Territory consists of water and forest to shelter prey ■ Occasionally patrols the territories to mark with urine and feces

○ Maple trees ■ Antifreeze proteins allow cells to survive -40 ℃ ■ Cannot survive in high temperatures because of transpiration (loss of water)

Using transects

● Transects can correlate the distribution of an organism with an abiotic factor ● Types of transects

○ Line transects: counts the number of organisms touching the tape laid between 2 poles ○ Belt transects: counts the number of organisms inside a quadrat randomly placed between two tapes ○ Point transects: birds are observed from randomly selected points within a specific radius

Niche concept

● Niche: specialised role of an organism in an ecosystem (e.g. territory, interactions with other organisms, habits) Competitive exclusion principle

● Two species with same niche cannot occupy the same habitat Fundamental and realised niches

● Fundamental niche: potential mode of existence ● Realised niche: actual mode of existence (result of adaptations and competitions)

Types of interspecific interaction between species

● Herbivory: primary consumers feeding on producers ● Predation: consumers feeding on other consumers ● Parasitism: organism makes use of another or feeds on it without killing immediately ● Mutualism: both organisms benefit from each other ● Commensalism: one organism benefits from another without benefiting or harming them

Mutualism between zooxanthellae and corals

● Zooxanthellae: photosynthetic algae inside corals (mutualistic) ● Zooxanthellae provide corals with glucose and amino acids ● Corals provide zooxanthellae with protected environment and allows them to photosynthesise in a stable environment

Interspecific interactions in Bahamian island

● Parasitism: dodders are non-photosynthetic vines that invade other plant tissues to obtain structural support and nutrients

● Commensalism: hawkfish are immune to stinging of fire corals and inhabit them (protection) ● Mutualism: hummingbirds get nectar from plants in exchange for pollination

Keystone species

● Keystone species: species in which its presence can maintain the biodiversity of an ecosystem ● Top-down influence on lower trophic levels → prevent lower trophic species from taking over resources (e.g. space,

food) ● E.g. Sea otters feed on sea urchins to prevent them from overpopulating in kelp forests (invading space)

C.2 Communities and Ecosystems Trophic level

● Trophic level: an organism’s feeding position in a food chain ● Organisms can occupy more than one trophic level ● To determine an organism’s trophic level:

○ Contents of a pellet from organisms can be observed ○ Observe characteristics from adaptations (e.g. sharp tooth)

Food webs

● Food web summarises all possible food chains in a community Food conversion ratios

● Food conversion ratio: quantity of dietary input (grams) required to produce a certain quantity of body mass (sustainability)

● Higher feed conversion ratio; less efficient (more input required) Impact of climate on ecosystem type

● Climates consist of differences in temperature and precipitation → influences productivity ● Precipitation and temperature can affect the rates of many chemical reactions in organisms (e.g. photosynthesis) ● Lets us predict the kind of stable ecosystem which will develop in the area (e.g. high rainfall and temperature →

tropical rainforest) Interpreting a Whittaker climograph

● Climograph: shows relative combination of temperature and precipitation in an area (abundance) Comparison of pyramids of energy from different ecosystems

● Length of food chains depend on the level of net primary productivity ● Pyramids of energy differ between ecosystems since energy conversion efficiencies are affected by the organisms

Gersmehl nutrient cycle diagrams

● Gersmehl diagram: model showing nutrient storage and flow for terrestrial ecosystems

● Storage (pool) represented by circles (size represents amount of storage)

● Flow of nutrients (flux) represented by arrows (thickness represents rates of flow)

Primary succession

● Ecological successions: changes which can transform ecosystems over time ● Abiotic factors limit the abundance of living organisms. ● Living organisms can affect abiotic factors, making the environment limiting to some → better adapted species join

the community ● Primary successions begins with changes in the environment (e.g. new volcanic island)

1. Few organisms at the start of succession (e.g. bacteria, lichen) → breaks down rocks 2. Shallow soils form, small plants start to grow 3. Deeper soils form for larger plants 4. Consumer populations change with the plant populations

Respiration rates & biomass accumulation

● Net production = Gross production - Respiration ○ Gross production: total amount of organic matter produced (unit area per unit time) ○ Net production: amount of gross production left after energy used in respiration

Secondary succession

● Secondary successions involve the replacement of an ecosystem following an environmental change (e.g. disused construction areas)

● Immediately after the ecosystem is cleared, biomass accumulate rapidly and productivity increases until it reaches a “climax”

Studying secondary succession

● Possible variables which could be studied ○ Species diversity ○ Stem diversity

○ Above ground biomass ○ Leaf area index ○ Light levels

Closed ecosystems

● E.g. mesocosms ● Energy is exchanged with the surroundings but not matter (e.g. water and nutrients are recycled within)

Disruptions to nutrient cycling

● E.g. in agriculture, human activities interferes with nutrient cycling 1. Humans harvest crops and take away the nutrients from the soil (ecosystem) 2. Thus, fertilisers (phosphate and nitrogen) must be added regularly to the soil 3. Too much fertilisers may lead to eutrophication

C.3 Impacts of Humans on Ecosystems

Alien and invasive species ● Alien species can become invasive species if normal limiting factors in their original habitats are missing (e.g.

predators, diseases, competitors) ● E.g. Cane toads from Central and South America were brought into Australia to control population of cane beetle →

reproduced rapidly and threatened native species. Also secretes poison from its back, preventing predators from eating it

Alien species and endemic species

● Competitive exclusion principle doesn’t allow alien species and endemic species (native species) to occupy the same niche → competition occurs

Risk of biological control

● Biological control can limit invasive species (introducing natural predators) ● Introduced predators can become invasive themselves ● Biological control can be tested by simulating the release of the predator in an enclosed facility

Cane toads in Australia

● Cane toads from Central and South America were brought into Australia to control population of cane beetle ● Reproduced rapidly and threatened native species ● Secretes poison from its back, preventing predators from eating it

Eradication programmes

● Eradication programme: selectively removing invasive species ● Requirements for success:

○ Removal of invaders needs to be faster their reproduction ○ Long-term commitment ○ Support of local communities ○ Prevention of re-invasion

Biomagnification

● Bioaccumulation: building up of toxins in organisms (cannot be easily excreted) ● Biomagnification:chemical substances (e.g. methylmercury) become more concentrated at each trophic levels (more

lethal) ● Level of toxin increases at each trophic level because the predator accumulates a large number of contaminated prey

Benefits and risks of DDT use

● DDT (dichlorodiphenyltrichloroethane): insecticide first used during WWII and later on as an agricultural insecticide ● DDT usage in agriculture was disapproved in 1962 after claims of biomagnification (low reproduction success rates in

birds, thin shells) ● However because rates of malaria soon increased after the ban, DDT usage was reapproved ● DDT can threaten human health (e.g. reduced fertility, cancer)

Plastics in the ocean

● Macroplastic degrades physically and chemically to form microplastic fragment ● Consequences:

○ Degradation of plastic releases organic chemicals which can bioaccumulate and biomagnify

○ Plastics can absorb other organic chemicals ○ Animals eat or become tangled in plastic (e.g. laysan albatross)

C.4 Conservation of Biodiversity

Indicator species ● Indicator species: organism only present in a specific environmental condition (presence or absence indicates certain

environmental condition) Calculation of a biotic index

● Biotic index indicates the quality of the environment using the relative frequency of indicator species ● Low biotic index: abundance of pollution insensitive organisms (polluted environment) ● High biotic index: abundance of pollution sensitive organisms (clean environment)

In situ and Ex situ conservation

● Method of conserving endangered species may be either in situ or ex situ In situ Ex situ

-Conservation inside the species’ natural habitat (e.g. national park) -Species is allowed to interact with other wild species (conserves niche) -Humans may be involved with management (e.g. removing certain species, controlling access)

-Conservation outside the species’ natural habitat (e.g. botanical garden, captive breeding) -Takes place when species cannot safely remain in their natural habitat

Captive breeding to restore populations of endangered species

● Breeding of animals in controlled environments (e.g. zoos) Components of biodiversity

● Richness: number of different species ● Evenness: how close in numbers each species is

Simpson’s diversity index

● Higher value (D) indicates greater biodiversity (richness and evenness) ● E.g. D = 1: only 1 species in a community

Biogeography and biodiversity

● Size of nature reserves: larger nature reserves allow species to stay in larger populations → more survivability ● Connections between nature reserves: more connections allow species to spread ● Shape of nature reserves: ecology near the edge is different from the centre (ideally circular)

C.5 Population Ecology (AHL)

Estimating population size ● Individuals are counted within a specified area to estimate population size (only if individuals are large and area is

small) ● Population size in small area is used to estimate entire population (population sampling)

Lincoln index to estimate population size

● Process (capture-mark-release-recapture method) 1. Capture as many individuals as possible in the habitat of the species (count) 2. Mark each individual 3. Release captured individuals in original habitat 4. Recapture and count how many are marked and how many are unmarked 5. Calculate population size using Lincoln index

Maintenance of commercial fish populations

● Data of fish (e.g. size, age) is collected to set catch limits ● Restrictions

○ Catching of younger fish (higher reproductive potential) are restricted ○ Catching of endangered fish are restricted

○ Closed seasons allow for undisturbed breeding of fish ○ Some fishing methods are banned (e.g. drift nets catch species outside of target)

Evaluating methods of determining fish population size

Method Advantage Disadvantage Random sampling NA Useless because fish are too mobile Capture-mark-release-recapture method

Can be used in lakes and rivers (small space)

Useless in large space because number of recaptured fish are too few

Echo sounders Can estimate the size of grouped fish Not all fish form groups Data from fish catches Age of fish (seen on ear bones) can

estimate spawn rates Not all data are accurate because of violators

Population growth curves

● “J”-shaped curve: when population grows exponentially in ideal conditions

● “S”-shaped curve: when population occupies a new habitat, they grow exponentially because there are no environmental resistance. Once the environmental resistance is introduced, the population growth reaches a transition point in which the growth decreases until the plateau phase.

Factors that influence population size

● Competition for resources ● Increase in predation ● Disease ● Migration (immigration/emigration) ● (plateau phase is reached when mortality and natality equals out)

Carrying capacity

● Carrying capacity: maximum size of a population that an environment can hold ● Population reaches carrying capacity → population stops growing, mortality and natality equal

Discussing the factors that influence population growth

● Mortality: young and old are affected the most for density dependent factors (e.g. food, predation), whereas density independent factors (e.g. climate) can affect the whole population regardless of age

● Natality: age and health status affects natality rate ● Emigration: occurs when individuals are unable to outcompete others ● Immigration: diversifies the gene pool → greater survivability

Top-down and bottom-up limiting factors

● Bottom-up limiting factor: resource availability (affects lower trophic level → higher trophic level) ● Top-down limiting factor: predation (affects higher trophic level → lower trophic level)

C.6 The Nitrogen and Phosphorus Cycles (AHL)

Nitrogen fixation ● Nitrogen fixation: Nitrogen (N2) needs to be fixed into ammonia (NH3) before being absorbed by plants ● Rhizobium (in root nodules) and azotobacter (in soil) can fix nitrogen

Nitrogen fixation by Rhizobium

● Rhizobiums are mutualistic with roots of plants (inside root nodules) ● Rhizobiums fix nitrogen and roots provide carbohydrates (energy)

Nitrification and denitrification

● Nitrification: ○ Nitrosomonas oxidise (+ oxygen) ammonia into nitrite (NH3 → NO2-) to produce energy ○ Nitrobacter oxidise nitrite into nitrate (NO2- → NO3-) to produce energy

● Denitrification: reduction of nitrate in soil (when there is no oxygen) ○ Pseudomonas reduce (- oxygen) nitrate into nitrogen (NO3- → N2)

Nitrogen cycle summary Impact of waterlogging in nitrogen cycle

● Nutrients from soil can enter water sources → eutrophication ● Loss of bioavailable nitrogen through denitrification

Carnivorous plants are adapted to low nitrogen soils

● Bogs and wetlands are low in nutrients → plants adapted to obtain nitrogen by digesting animals ● Adaptations

○ Modified leaves to trap animals ○ Extracellular digestion (enzymes are secreted outside)

Phosphorus cycle

● Phosphorus use ○ Required to produce molecules such as ATP, DNA, and RNA ○ Maintain skeleton in vertebrates ○ Build cell membranes

● Summary 1. Phosphorus are found in marine sediments and mineral deposits (phosphorite) 2. Rocks containing phosphate undergo weathering, phosphates enter soil 3. Plants taken up phosphates in soil 4. Consumers get phosphates from plants 5. Organic waste containing phosphate go back into the cycle

Effect of agriculture on soil phosphorus ● Phosphorus can be added to soil by applying phosphate-based fertilisers ● Phosphorus can be removed by harvesting crops containing phosphorus

Peak phosphorus

● Peak phosphorus: point in time in which maximum phosphate production is reached and begins to fall because of lack of phosphorus

● Because fertilisers rely on phosphate, agricultural products also falls ● Phosphate cannot be artificially synthesised

Eutrophication and biochemical oxygen demand

● Process 1. Water-soluble nutrients in soil (e.g. phosphates, nitrates) enter water sources during rain 2. Excess nutrients enter water → eutrophication 3. Nutrients cause algal blooms on water surface 4. Algae blocks light for underwater plants 5. Plants and algae eventually die and bacteria appear → oxygen is used up to break down dead matter

(biological oxygen demand) ● Higher biological oxygen demand (less available oxygen) limit population of certain fish

Solutions to disruptions to the phosphorus cycle

● Recovery of phosphate from sewage ○ Use of bacteria to selectively accumulate phosphorus from sewage → sludge containing bacteria can be used

as fertiliser ○ Chemical precipitation with iron chloride or alum can remove phosphorus from sewage (greater yield than

bacteria) ● Phosphate runoff from livestock manure

○ Genetically modified pigs prevent them from excreting phosphate (pig absorbs phosphate) Methods of soil testing

● Soil quality assessment kits ● Soil nutrition deficiencies show in characteristic symptoms in leaves