Unit 3 Topic 2: ecosystem dynamics

How is solar energy converted into biomass? Explain how this energy flows through an ecosystem.

Solar energy is captured by plants through photosynthesis, converting it into chemical energy in biomass, which then flows through an ecosystem as animals eat plants and are eaten by other animals.

Explain how energy is lost through energy transfers and transformations. Include: energy lost through radiation, reflection and absorption.

some is lost as heat, some is reflected by surfaces (like leaves or water), some is absorbed by non-living parts of the environment, and some is radiated away, meaning that only a fraction of the original energy is passed on to the next level in the food chain.

define biomass

total mass of living organisms in a given area or ecosystem at a given time, usually measured in grams or kilograms. It represents the amount of stored energy in living material.

list the trophic levels of a terrestrial biomass pyramid

primary producers, primary consumers, secondary consumers, and tertiary consumers

describe how matter is transferred and transformed as it cycles through the water cycle

Water moves between land, living things, and the atmosphere.

Changes form by evaporation, condensation, precipitation, runoff, and transpiration.

describe how matter is transferred and transformed as it cycles through the carbon cycle

Carbon moves through air, plants, animals, soil, and fossil fuels.

Photosynthesis stores CO₂ in plants, respiration and decomposition release it, and burning fuels adds extra CO₂.

describe how matter is transferred and transformed as it cycles through the nitrogen cycle

Nitrogen moves between the air, soil, plants, animals, and bacteria.

Bacteria fix nitrogen so plants can use it, animals eat plants, and decomposers return nitrogen to the soil or air.

define ecological niche

role of species in an ecosystem, inclduing its habitat, feeding relationships and interactions with other species.

define competitive exclusion principle

2 species competing for the same limited resources.

define keystone species

help maintain the structure and balance of a community.

outcomes of removing keystone species

prey populations increase, decline or extinction of other species that depend on it, and overall change in the structure and balance of an ecosystem.

define carrying capacity

maximum number of individuals of a species that an environment can support over time without depleting its resources or damaging the ecosystem.

explain why the carrying capacity of a population is determined by limiting factors (biotic and abiotic)

These factors restrict population growth by impacting birth rates, death rates, or both, and ultimately dictate how many individuals an ecosystem can support. 

what is the formula for population growth rate

(birth+immigration)-(death+emigration)

what is the lincoln index used for

estimate the population size of animals in a habitat by capturing, marking, releasing, and then recapturing individuals.

how to determine the mode (exponential growth J-curve, logistic growth S-curve) of population growth

exponential growth (J-curve) appears as a steep upward line that keeps rising, while logistic growth (S-curve) starts with rapid growth but then levels off into a plateau at the carrying capacity.

effect of changes within population-limiting factors on the carrying capacity of the ecosystem.

When these factors become more favorable (e.g., increased food availability, more shelter), carrying capacity can increase, allowing a larger population to be sustained. Conversely, when these factors become less favorable (e.g., decreased food availability, increased disease prevalence), carrying capacity decreases, and the population size may decline. 

explain primary succession

Primary succession begins with nudation, where pioneer plants (often r-selected) colonise bare surfaces and gradually form soil for larger species.

explain secondary succession

occurs after a disturbance, with existing soil allowing faster regrowth by mainly k-selected species.

explain climax community

is the stable, final sere, dominated by k-selected species in balance with the environment.

differentiate primary and secondary succession

Primary succession begins in a lifeless, barren environment like bare rock or a newly formed volcanic island, where no soil exists. Secondary succession, occurs after a disturbance (like a fire or flood) has disrupted an existing ecosystem, but some soil and remnants of the previous community remain. 

List three features of pioneer species that make them effective colonisers.

Fast growth and reproduction – they are often r-selected and reproduce quickly.

Ability to survive in harsh conditions – they can grow on bare rock or poor soil.

Soil-building ability – they help break down rock and accumulate organic matter, allowing other species to grow.

impact of human activity on the reduction of biodiversity and on the magnitude, duration and speed of ecosystem change.

• destroying habitats, polluting environments, overhunting species, and introducing invasive species.

• This loss of species often causes ecosystems to change faster, with greater magnitude (more dramatic shifts in species composition) and longer duration (ecosystems take longer to recover or may never fully recover), disrupting ecological balance.

how does urbanisation reduce biodiversity and ecosystem change

• Converts natural habitats into cities and roads, reducing available habitat for plants and animals.

• Fragmented habitats make it hard for species to survive or migrate, leading to loss of biodiversity.

how does habitat destruction reduce biodiversity and ecosystem change.

• Clearing forests, wetlands, or grasslands removes the homes of many species.

• This directly reduces species numbers and can cause ecosystem collapse or major change.

how does salinity reduce biodiversity and ecosystem change.

• Irrigation and poor land management can increase soil or water salinity.

• High salt levels kill sensitive plants and animals, altering species composition and reducing biodiversity.

how does land and soil degradation reduce biodiversity and ecosystem change.

• Overgrazing, deforestation, and erosion reduce soil fertility.

• Plants and microorganisms struggle to survive, causing changes in ecosystems and a decline in biodiversity.