IB Biology: D4.2 Stability and change

ecosystem stability

ability to maintain it’s structure and function over time, despite changes and disturbances. It should be able to go back to it’s original state. resistance and resilience

exampleS of stable ecosystems

• tropical rainforests; despite natural disasters, number of species remains relatively constant, but recovery is slow

• coral reefs

• borea forests/ taiga; withstand cold, long winders, many coniferous trees

• Deserts; despite year long heat, species survive

factors which affect stability of ecosystems

• Supply of energy; sun for producers

• Recycling of nutrients; carbon, nitrogen and phosphorus. ie photosynthesis→ glucose → eaten → respiration → CO2 in atmosphere. runoff minimisation

• Biodiversity; multiples species to fulfil ecological roles→ resilient ecosystem (ie multiples fish species can graze algae controlling it, not dead if one species disappears) + allows to have wider range of traits and variations which can help adapt easier to new conditions

• Climatic factors; rapid changes in climatic conditions can disrupt the balance of the ecosystems as not all species are adapted

tipping points ecosystems

threshold which results in irreversible change in ecosystem’s structure, function and composition. once passed, can lead to loss of biodiversity, collapse of populations and degradation of ecosystem services

tipping points ecosystems amazon example

• deforestation; in small quantities, surrounding forest can help recovery, but rate of recovery is oftentimes very slow

• less trees, less transpirations→ less cooling, less rainclouds, less precipitation. because amazon rainforest so large, affects the whole world

• tipping point is not clear, but already 20% of rainforst has been cut down for agricultural production, logging and mining

mesocosms

meso - medium

cosm - world

small scale reimitations of the ecosystems

no exchange of matter once sealed, but energy can be brought in ( heat or sunlight)

factors which mesocosms can investigate

• pH of water

• temperature

• light intensity

• colour of light

• concentration of ions

• population size of producers

• diversity of producers

• population size of consumers

• community composition.

keystone species

specie with disproportionally large impact on an ecosystem; plays critical role in it’s stability, such as apex predators, bees..

control abundance of other specie in the ecosystem

trophic cascades description

if keystone species declines/ is removed, balance of food web can be hindered, causing destabilisation of entire ecosystems just because of one species

tropic cascades example

• sea otters prey on sea urchins and control population size

• if sea otters die, sea urchins can reproduce unhindered, population boom ensures

• sea urchins overgraze kelp forest, which is bad as kelp forests are carbon sinks

• other organisms dependent on kelp for habitat are negatively affected

keystone species effect on habitat

beavers; create dams, which alter flow, which create new habitats for species. if they disappear, the habitats the created and species dependent on them are endangered. plus, droughts can appear as water storage abilities of ecosystem are hindered

yellowstone wolves case study

• wolves were hunted to extinction

• elk population increases, tree species such as aspen and cottonwood suffered from overgrazing

• plant diversity lowered, and land erosion increased

• elk control prevented further degradation but didn’t improve condition

ecological impact of harvesting ( hunting/fishing ) from the wild

• goal of harvesting sustainably is removing maximum biomass that can be harvested indefinetly without decreasing stability of ecosystem

• continual monitoring is needed (population abundance, sex ratio, harvest composition…)

• maintenance of ecosystem

sustainability

the capacity of meeting the needs of the present generation without compromising the ability of future generations

soil erosion

caused by excessive tillage and monocropping + deforestation

excessive detachment of soil particles from one place to the other, decreasing productivity of soil

agrochemicals

• synthetic fertlisers and pesticides can contribute to soil acidification, increasing erosion,

• synthetic fertilisers cause decline in soil synthetic matter, reducing ability to hold nutrients

factors defining sustainability of agriculture

• agrochemical use

• water use

• biodiversity

• carbon footprint

eutrophication

process in which water bodies become enriched with excessive nutrients ( nitrogen and phosphorus ), causing algal blooms. disturbs balance of ecosystems, and has detrimental effects on water quality

steps of eutrophication

1. nutrient enrichment, due to industrial runoff, sewage and industrial activities.

2. rapid reproduction of algae and aquatic plants

3. large quantities of organic matter accumulate, which settles at the bottom of the water body

4. decomposers break down the organic matter, consuming large quantities of oxygen, decreasing it’s level in the water

5. oxygen depletion can cause death of fish

bioaccumulation

pollutants which are ingested, and resist breakdown, accumulating in tissues over time

biomagnification

process in which an organisms consume a high number of other organisms containing pollutants, leading to their accumulation at high tropic level. the concentration of the pollutant increases with every tropic level

main example: mercury

effects of plastics on oceans

• disruption of marine food webs; filter feeding on plankton, eat many microplastics → bioaccumulation

• chemical pollution; can release toxic chemicals

• wildlife entanglement and ingestion → blockages in digestive systems, malnutrition and starvation

• habitat degradation; plastic accumulation can mess up some ecosystems, such as corals

restoration; what can be done

• species reintroduction; ie wolves in yellowstone, brings back keystone species

• habitat restoration; reforestation, connecting fragmented habitats

• rewilding urban areas; green spaces, parks, roottop gardens. give opportunities for wildlife to thrive

• rewilding rivers/waterways: removing dams, allowing rivers to meander

• regulations on harmful practices; reducing intensive farming

rewilding in terms of restoration

attempts at reintroducing biological, native systems

ecological succession

natural, gradual progression of changes in species composition and community structure over time, after a disturbance

causes of ecological succession

• natural disturbances; wildfires, volcanic eruptions, floods. gives opportunities for pionner species to colonise area

• human activities; deforestation, agriculture, urbanisation and mining can disturb natural ecosystems and cause changes

• changes in environmental conditions (natural and human-driven); shifts in temperature, precipitation and soil fertility can make it so new species better adapted to the environment outcompete local ones

primary succession definiton

process of ecological change that happens in an environment entirely devoid of life initially

changes/ changes during primary succession

bare rocks → lichen → herbacious plants → shrubs → tress

pionner species

usually small, hardy organisms which can survive on rock, without organic matter, and help break it down to create soil layer

pedogenesis

soil formation from weathering of harder rocks

secondary succesion in ecosystems

process of ecological change in area that has previously been inhabited by living organisms but that suffered a disturbance which distrubed existing community. ie a fire/ hurricane

cyclic succession

community changes regularly, going by the stages of succesion. it can be seasonal

climax communities

stable and mature ecological community that remains relatively unchanged over an extended period of time. final stage of ecological succesion

arrested succession

when the progression of normal ecological succesion is halted or slowed due to external factors, such as frequent stressors. ie frequent fire in california, or cattle gazing, where shrubs are consumed in their early development stages