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Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
Unit6 ecosystems
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Unit6 ecosystems

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  • 1. UNIT 6: ECOSYSTEMS
  • 2. What Is An Ecosystem? An ECOSYSTEM is formed by a group of living organisms (community) that interact with each other and with the surrounding physical environment. All ecosystems have two parts: - Biotic factors (living things), which form the BIOCENOSE - Abiotic factors (non-living): water, soil, light, temperature, pH, etc. The non-living part of an ecosystem is also called HABITAT or BIOTOPE. ECOSYSTEM = BIOTOPE + BIOCENOSE
  • 3. Ecosystems are made of MATTER and ENERGY: MATTER: - in the habitat: inorganic matter in rocks and minerals, soil, water, etc - in the living beings: organic matter - limited - MATTER IS RECYCLED in the ecosystems: PRODUCERS: transform inorganic matter into organic matter that will form all the living beings of the ecosystem CONSUMERS: get their matter from producers or other consumers. DECOMPOSERS: recycle organic matter transforming it into inorganic matter.
  • 4. ENERGY: - The SUN is the main energy source for most ecosystems: unlimited - AUTOTROPHIC organisms (plants, algae and some bacteria) transform a small part of the solar energy and use it to transform inorganic matter into organic matter (rich in energy: chemical energy) - HETEROTROPHIC organisms (animals, protozoa, fungi, bacteria) get their energy from the autotrophs or other heterotrophs: trophic chains - Only a small part of the energy passes on to the next trophic level. Most part is lost (faeces, heat, non-ingested food...). - ENERGY FLOWS in the ecosystems.
  • 5. FOOD (or trophic) CHAINS: Chain that links species that eat and are eaten by others; each level is a TROPHIC LEVEL: HETEROTROPHS or CONSUMERS: get their organic matter from other organisms: - primary consumers (herbivores) - secondary consumers (carnivores) - tertiary consumers (supercarnivores) AUTOTROPHS or PRODUCERS: make their own organic matter. DECOMPOSERS: are not represented in food chains. They recycle organic matter by breaking down organic matter from dead organisms.
  • 6. FOOD (or trophic) CHAINS are usually more complex: FOOD WEBS
  • 7. TROPHIC PYRAMIDS: - of NUMBER of individuals - of BIOMASS - of ENERGY
  • 8. Some times pyramids of numbers and biomass can be “inverted”. Energy pyramids can NEVER be inverted. WHY?
  • 9. There are big losses of energy as it flows from one trophic level to the next one. Only 10% (on average) of the energy in one level passes to the next one. This is known as the 10% rule.
  • 10. PHOSPHORUS CYCLE
  • 11. CARBON CYCLE Key terms: - RESPIRATION - PHOTOSYNTHESIS - COMBUSTION
  • 12. NITROGEN CYCLE Key Terms: - FIXATION - ASSIMILATION - NITRIFICATION - DENITRIFICATION
  • 13. Self-regulation of the Ecosystems: POPULATION: a group of individuals of the same species living in the same place at the same time and interbreeding. How much can a population grow? - birth rate - death rate - immigration - emigration When a species colonises a new area, if the conditions are favourable, it will have an EXPONENTIAL GROWTH: (J-shaped curve) But... can this go on indefinitely? What will happen when resources start to be scarce (food, space) or the environment is not so favourable (diseases, adverse climate....)?
  • 14. When a population grows, normally limiting factors will appear, that will limit the population size: Limiting Factors of an Ecosystem: - Abiotic factors: food, light, temperature, water, soil... - Biotic factors: relationships with other living beings: Intraespecific Relationships: COMPETENCE Interspecific Relaitionships: COMPETENCE, MUTUALISM, SYMBIOSIS, COMMENSALISM, PARASITISM, PREDATION We can classify these factors as: - dependent on the population density: diseases, competence (and most biotic relationships)... - independent on the population density: temperature, light, draughts...
  • 15. ENVIRONMENTAL RESISTANCE includes all the factors that may limit the growth of a populations (both biotic and abiotic) BIOTIC POTENTIAL of a population is the maximum rate at which it can reproduce, given all the resources it needs (max. birth rate, min. death rate)
  • 16. So, in real-life conditions, a population encounters environmental resistance, and the typical graph that shows how it grows is the S-shaped curve (LOGISTIC GROWTH): CARRYING CAPACITY (K) is the maximum population size that can be supported by a particular environment.
  • 17. Evolution of the human population. What kind of growth does it follow? Why do you think it is so?
  • 18. Once that a population has reached its carrying capacity, its size remains stable around it, with small periodic variations that are called FLUCTUATIONS. Changes in the environment (plagues, diseases, new predators, competence.... ) may lead to a new carrying capacity for a population:
  • 19. Strategies for Survival: r-strategy and k-strategy R-strategy species: K-strategy species: - reproduce rapidly (high birth rates) - slow reproduction (low birth - abundant offspring rates) - little investment in care of the - produce few offspring offspring: much of the offspring dies - big investment in care of the - live in changing, unstable offspring, which takes time to environments develop and grow adult. - bacteria, insects, fish... (small- - live in stable environments, to sized species) which they are well adapted. - big-sized species
  • 20. Ecosystems change over time: ECOLOGICAL SUCCESSIONS An ECOLOGICAL SUCCESSION is an ordered sequence of changes in the composition (species) and structure of a community over time, until it reaches a stable state called climax community. - Successions happen because the living beings modify their environment by making it more favourable for more complex organisms. Environmental factors such as climate (draught, floods...) fires, volcano eruptions, may also alter the ecosystems.
  • 21. Given enough time and favourable conditions, a pond may transform into a forest.
  • 22. If a succession begins in a new area, where no previous community was established (e.g. on a sand dune, or on a new volcanic island, it is called a PRIMARY SUCCESSION. Pioneer species, with little nutritional needs, small size and resistant to unstable conditions, are the first to establish on the bare land. They are r-strategists such as lichens and mosses. The activity of these organisms produce the meteorization of the rock (both physical and chemical).
  • 23. When these first colonizers die, their organic matter helps to create a fertile soil, where other (a little more complex) organisms will establish: ferns, herbs and bushes, and finally, trees. FERNS HERBS, BUSHES
  • 24. As these new plants die, the humus (organic part of the soil) increases, and the soil becomes deeper and more structured. K-strategists start to replace r-strategists, as they are better competitors in stable environments.
  • 25. Animal species follow the changes in the plant species as the succession progresses.
  • 26. Finally -ideally- all the ecosystems progress in a succession until they reach a final state called CLIMAX COMMUNITY, where the maximal biodiversity and stability is achieved.
  • 27. Different CLIMAX COMMUNITIES in different latitudes. Carballeira Bosque de faias Tropical forest Aciñeira
  • 28. SECONDARY SUCCESSIONS happen on a place with the previous ecosystem was completely or partially destroyed by natural or artificial causes (fires, volcano eruptions, floods...). These ecosystems keep their soil, so secondary successions are normally faster than primary successions.

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