Ecosystems and Ecology

• It is advised to bring a calculator to the test

Food Chains and Food Webs

• Food chains should be drawn with a straight, horizontal line with one organism per trophic level, usually 3-5 levels.
• Arrows indicate energy transfer as one level consumes the level below.
• Identify a clear path in a food web that starts with a producer and ends with a secondary or tertiary consumer, ensuring no arrows point back to the consumer.
• An organism can occupy more than one trophic level.
• Adding or removing a species from a food web disrupts the ecosystem's balance.
• The disruption impacts populations, resource availability, and interactions, leading to cascading effects and affecting biodiversity, population dynamics, and ecosystem stability.
• The removal of a species can lead to a loss of food sources for some organisms, potentially causing their decline.
• Predator-prey imbalances may occur if a predator is removed, causing the prey population to increase and deplete resources.
• Overall decrease in biodiversity may happen when all animals are affected.
• The introduction of a new species can result in increased competition, potentially causing native species to decline or become extinct.
• If the species is a predator, new or existing prey species populations may dwindle, and predator populations might grow.
• Ecosystem overload/collapse may occur if invasive species disrupt food chains or webs, leading to resource depletion, habitat destruction, or disease spread.

Strengths and Weaknesses of Models

• Models vary in their strengths and weaknesses depending on the specificity of the information that they may give
• Strengths may include being easier to work with.
• Models may be used to predict the effect of a change of input.
• Models may be applied to other similar situations.
• Models may be used to find patterns.
• Models may be used visualise small items/entities.
• Weaknesses may include being less accurate and simplified.
• Models may have wrong assumed which result in the wrong model.
• Models may give inaccurate predictions.
• Models may not consider all variables.
• Models may show different effects using the same data.
• Models may be uncertain when predicting future data.
• Models can be interpreted in different ways.

Community vs. Ecosystem

• Community refers to the interacting populations within an ecosystem; these are the biotic factors.
• Ecosystem is a complex system where populations interact with each other and their physical, abiotic surroundings.

Keystone Species

• Keystone species maintain the structure of their ecosystem and have a disproportionate impact on its community.
• The removal of keystone species increases the risk of ecosystem collapse.

Factors Influencing Human Population Variation

• Migration, or people entering a country, increases the population size.
• Birth rates that are higher than death rates lead to population increases.
• Low birth rates, often seen in HICs with more elders, improved family planning, and urbanization, can limit population growth.
• Anti-natal policies (limiting the number of children), pension schemes, and higher taxes for more children can add to low birth rates.
• Greater independence/education for women can also reduce birth rates.
• High birth rates, common in LICs, result from more people of childbearing age and agricultural development.
• Improved public health/sanitation lowers death rates and stimulates population growth
• Lower income tax, free education/healthcare, the need to replace children who die, prestige, and perpetuating the family name all correlate with high birth rates.
• Low death rates result from a younger population, access to clean water, reliable food, good hygiene, low population densities, better healthcare, and rising living standards.
• High death rates are associated with older populations (HICs), infectious diseases, overcrowding, poverty, and lack of safe conditions.
• Increased life expectancy can increase population size if birth rates remain stable.

Socioeconomic and Environmental Implications of Population Changes

• Economic implications of increasing population may include economic growth boosted by more workers/consumers.
• Job market competition increases, leading to unemploymen and poverty.
• Economic implications of decreasing population may include less resource pressure reducing costs and overexploitation.
• Declining markets may shrink economies, affecting businesses and investments.
• Social implications of an increasing population may include cultural diversity/innovation
• Also includes overcrowding and social inequality due to housing and less space for people.
• Social implications of a decreasing population may include better living standards.
• Burden of an aging population means that there are fewer young people supporting retirees which causes stress on healthcare and pension systems.
• Environmental implications of an increasing population may include the potential for innovation in sustainability.
• Also includes a higher demand fofr natural resources which results in the depletion of resources from ecosystems.
• A declining population may see natural habitat recovery because there is less pressure on the environment.
• The workforce for conservation declines (fewer people working in sustainability and conservation efforts).

Modeling Human Population Growth

• Advantages include being able to predict growth, support economic planning, assists in resources planning.
• Advantages may include assisting in the identification of resource shortages.
• Disadvantages may include assuming human behavior can remain consistent over time.
• Models often are unable to account for sudden events, like pandemics or natural disasters, that can affect population growth.
• Models may simplify the complex interations between social, cultural, economic and political factors.
• Limited data quality can lead to incorrect models/predictions.

Estimating Human Carrying Capacity

• Estimating human carrying capacity is difficult because of humans' broad and changing ecological niche, which can alter carrying capacity.
• Humans can rapidly change and evolve, any estimates are therefore short-term.
• Humans have temporarily eliminated most limiting factors through developments, living beyond sustainability limits.
• The range of resources for humans is greater than other specues, with the ability to substitute resources. Changes in technology influences resource use, and leads to different lifestyles,

Altering Human Carrying Capacity

• Developing technological advancements expands resources and increase life span.
• Expanding the use of resources, humans can maximize availability by using substitutes.
• Through reusing, recycling, remanufacturing, and absolute reduction, carrying capacity can be decreased
• Usage of renewable sources can be reduced, thereby decreasing carrying capacity.
• Decrease can come via external factors like pandemics, famine, natural disasters, climate change, and natural disasters.

Demographic Transition Model (DTM)

• DTM model describes changing levels of births and deaths in a human population through various stages.
• Stage 1 (Pre-industrial) sees high/variable birth and death rates, fluctuating population growth, and short life expectancies.
• Stage 2 (Early Expanding) is characterized by high birth rates but rapidly declining death rates, slight increases in life expectancy, and rapid population growth.
• Stage 3 (Late Expanding) involves declining birth rates, low death rates, and continued population growth at a slower rate.
• Stage 4 (Low Stationary) features low/variable birth and death rates, stable population growth, higher dependency ratio, and longer life expectancy.
• Stage 5 (Declining) shows birth rates lower than rising death rates and declining population size
• Natural increase rate is the rate of human growth expressed as a percentage change per year.
• Doubling time is the time it takes for a population to double.

Strengths and Limitations of the DTM

• Strengths include it bening easy to undestand and showing simple changes over time.
• The model can be easily compared to different countries across the world and show how population and developemnt go hand in hand.
• Limitations include assuming models will follow the eurocentric process. The fall in DR (death rate) is not always so quick, and the time scale can vary in some countries/regions. Limitations include not accounting for deaths from infectious diseases or other pandemics

Factors that Influence Movement Between DTM Stages

• Influence comes from the improvements in healthcare and sanitation and increased access to education.
• This influence can be urbanization, industrialization, economic, development, political change, and stability and improvements in education.

Photosynthesis and Respiration

• Photosynthesis is a process where light energy is converted to chemical energy.
• Inputs are carbon dioxide and water, and outputs are glucose and oxygen.
• Respiration is the breakdown of glucose to release ATP for living processes.
• Inputs of respiration are glucose and oxygen, while outputs of respiration are carbon dioxide and water.

Roles of Producers, Decomposers, and Consumers

• Primary trophic level are the producers and autotrophs.
• Autotrophs produce energy for all trophic levels and provide habitats with niches, supply nutrients to soil, bind soil, and stop erosion.
• Decomposers are bacteria/fungi that break down dead organisms, release nutrients back into the cycle, and control disease spread.
• Consumers occupy trophic levels of 2-4 and are heterotrophs, maintaining balance through herbivory-predation and competition, seed dispersal, pollination, and removing weak.

Energy Transfer in Food Chain

• The energy that they transfer is then degraded into a less useful form, and it is lost as heat.
• The energy from heat is lost so it doesn't reach the next level.
• Trophic inefficiencies result from incomplete consumption, inefficient digestion, and energy use in reproduction.

Loss of Solar Energy Before Biomass Conversion

• Most of the solar energy either does not enter the plant or is immediately reflected.
• Most wavelengths of light, reaching the plant are unsuitable.

Biosphere Integrity

• Biosphere integrity is the overall health and function of ecosystems and biodiversity.
• Ways to protect integrity include the following:
• Preserving natural habitats to have a safe place for many species to be home.
• Providing essential ecosystem services to have continued survival/reproduction of species.
• Implementing sustainable land/resource management to prevent habitat waste and damage.
• Following ethical fishing/forestry practices.
• Implementing sustainable agriculture approaches.
• Motivating people to become environmental stewards via education/public awareness

Loss of Ecosystem Sustainability

• Ecosystem unsustainability, such as in forests, is caused by human activities like logging and agriculture.
• Dense tree canopies are lost through unsustainable practices, and the layered structure is reduced, causing reduction of habitats and diversity.
• Forest floors when exposed to sunlight/rain become vulnerable to nutrient loss.
• There is loss of tree cover causes loss of transpiration of water causes rainfall and cooling resulting in climate change.
• Overall plant species are reduced to those suited to climate change.

Total Fertility Rate (TFR)

• Total fertility rate is the average number of children per woman in her lifetime.
• Replacement fertility is 2.1 due to number of children and maintain the population growth rate at 0.
• FR is the amount of births per 1000 women of childbearing age and 15-44 years of age.

High vs Low Fertility Rates

• Infertility compared to death rate, higher fertility rates increase population size.
• Reasons for higher rates are high infant/childhood mortality and cultural/societal choices.
• More children often leads to more family income. Security in old age, status in women, unavailability of contraceptives, inheritance is due to the need to have a male heir (a son).
• Lower fertility rates include providing education and literacy, improved health, contraceptives, and increased income.

Increase Population

• Countries increase population by resorting to pro-migration and pro-natalist policies.
• In Singapore, the population began to shrink, and it became difficult to encourage women to birth for maternity leave.
• To do so, that made it free for the first 4 children, with subsidized childcare.