POPULATIONS IN ECOSYSTEMS

• ECOSYSTEM: a community and the non-living components of its environment together form an ecosystem.

  • populations of different species form a community
  • ecosystems can range in size from very small to very large
• 7 MAIN ECOSYSTEMS: (1)

  • FOREST: dominated by trees- interactions between plants, animals, microbes, local soils and atmosphere
  • DESERT: layer of soil that can be sandy, gravelly or stony depending on type of desert. Less than 50cm of rain a year
  • RAINFOREST: hot, moist biome where it rains all year with dense canopies of vegetation that form 3 different layers
  • GRASSLAND: vegetation dominates by grasses and other herbaceous (non-woody) plants
  • TUNDRA: treeless regions in the Arctic and on top of mountains, cold and windy climate, scant rainfall. Covered in snow majority of year.
• 7 MAIN ECOSYSTEMS: (2)

  • SAVANNA: terrestrial habitat where plants and animals are living together in an open area covered with grasses and some scattered bushes and trees
  • MOUNTAIN: area with harsh environmental conditions. These include often long lasting snow cover, short growing seasons and topographically related disturbances such as avalanches, rockfalls or landslides
• NICHE: the roles of a species within a habitat

  • the niche includes biotic interactions (what it eats / is eaten by) and abiotic interactions (oxygen in, carbon dioxide out)
  • all species have a unique niche, occupied by only one species, this is the competitive inclusion
  • of two species try to occupy the same niche, one species outcompetes the other species
  • species are adapted to different niches
  • if two species look like they own the same niche, there will be slight differences like different frequencies for their echolocation
• ADAPTATIONS: features that increase and organisms chance of survival and reproduction

  • can be psychological, behavioural, or anatomical
  • NATURAL SELECTION = better adapted survive so reproduce and pass on alleles, frequency increases
  • every species is adapted to use an ecosystem in a unique way (niche)
• WHAT ARE THE DIFFERENT TYPES OF ADAPTATION

  • physiological
  • behavioural
  • anatomical
• BIOTIC ADAPTATIONS

  1. For food to survive

  • sea otters use rocks to smash open shellfish and clams

  2. For mates to reproduce

  • make frogs produce mating calls to attract females of same species (courtship behaviour)

  3. Less competition

  • bacteria produce antibiotics that kill other species of bacteria in the same area
• ABIOTIC ADAPTATIONS

  1. conserve energy

  • hedgehogs hibernate and lower their rate of metabolism (chemical reactions) over winter to conserve energy during cold months

  2. Live in areas with less competition

  • seals have thick blubber, keep warm in coldest seas, less competition, more food

  3. Live and hunt

  • otters have webbed paws, can walk on land and swim effectively, hunt and live on land or in water
• POPULATION SIZE: the total number of organisms of one species in a habitat

  • populations are dynamic in that they vary in size and composition over time
  • where a population grows in size slowly over a period of time it’s possible to plot a graph of numbers in a population against time. Where the population grows rapidly over a short period of time this might not be possible. This is the case with measuring growth of microorganisms.
  • no population continues to grow indefinitely bc certain factors limit growth - light Water
  • in ideal conditions, organisms grow fast and reproduce successfully
• FACTORS THAT LIMIT POPULATION GROWTH:

  • availability of food
  • light
  • water
  • oxygen
  • Shelter
  • accumulation of toxic waste
  • disease
  • predators
• CARRYING CAPACITY: the maximum stable population size of a species that an ecosystem can support

  • it varies as a result of abiotic and biotic factors
• ABIOTIC FACTORS THAT AFFECT POPULATION SIZE

  1. Temperature
  2. pH
  3. light
  4. water and humidity
• 1.TEMPERATURE (abiotic) EFFECTING POPULATION SIZE (1)

  • each species has a different optimum temperature at which it is best able to survive
  • further away from the optimum = the fewer individuals in a population are able to survive and the smaller is the population that can be supported
• 1.TEMPERATURE (abiotic) EFFECTING POPULATION SIZE (2)

  In plants and cold-blooded animals, the carrying capacity is reduced when:

  • temperatures fall below the optimum, the enzymes work more slowly so their metabolic rate is reduced. Populations therefore have a smaller carrying capacity.
  • temperatures rise above the optimum, the enzymes work less efficiently because they gradually undergo denaturation
• 1.TEMPERATURE (abiotic) EFFECTING POPULATION SIZE (3)

  In warm-blooded animals, they can maintain a relatively constant body temperature regardless of the external temperature. However the carrying capacity of the population is reduced when:

  • the temperature of the external environment gets further from their optimum temperature, the more energy these organisms expend un trying to maintain their normal body temperature. This leaves less energy for individual growth and so they mature more slowly and their reproductive rate slows.
• 2. pH (abiotic) AFFECTING POPULATION SIZE

  This affects the action of enzymes

  • each enzyme has an optimum pH at which it operates most effectively
  • a population of organisms is larger where the appropriate pH exists and smaller, or non-existent, where the pH is different from the optimum
• 3. LIGHT (abiotic) AFFECTING POPULATION SIZE

  As the ultimate source of energy for most ecosystems, it’s a basic necessity of life

  • rate of photosynthesis increases as light intensity increases
  • the greater the rate of photosynthesis, the faster plants grow and the more spores or seeds they produce
  • their carrying capacity is therefore potentially greater. In turn, the carrying capacity of animals that recd on plants is potentially larger
• 4. WATER HUMIDITY (abiotic) AFFECTING POPULATION SIZE

  • where water availability is low, populations are small and consist only of species that are well adapted to living in dry conditions
  • humidity affects the transpiration rates in plants and the evaporation of water from the bodies Of animals
  • in dry conditions, the populations or species adapted to tolerate low humidity will be larger than those with no such adaptations
• ABIOTIC FACTORS AFFECTING POPULATION SIZE

  • other abiotic factors include oxygen, carbon dioxide availability, soil moisture and pH, space available etc
  • when any abiotic factor is below the optimum for a population, fewer individuals are above to survive because their adaptations aren’t suited to the conditions. The carrying capacity is reduced and if no individuals have adaptations that allow survival, the population becomes extinct.
• BIOTIC FACTORS WHICH AFFECT POPULATION SIZE

  1. Competition
  2. predation
• 1.COMPETITION (biotic) AFFECTING POPULATION SIZE

  where two or more individuals share any resource (eg. Light, food, space, oxygen) that’s insufficient to satisfy all their requirements fully, then competition results

  • Intraspecific - same species
  • Interspecific - different species
• 2. PREDATION (abiotic) AFFECTING POPULATION SIZE

  an Intraspecific relationship between predator and prey
• INTRASPECIFIC COMPETITION: same species - Intraspecific competition occurs when individuals of the same species compete with one another for resources eg. Food, breeding sites
• INTERSPECIFIC COMPETITION: individuals of different species compete for resources eg. Food, water etc
• HOW INTRASPECIFIC COMPETITION AFFECTS POPULATION SIZE

  1. The population of a species increases when resources are plentiful as greater the availability, larger the population
  2. as population increases, more organisms will compete for same amount of space and food
  3. eventually resources become limiting and there isn’t enough for all organisms so population beings to decline as lower the availability, smaller the population
  4. smaller population = less competition for space and food which is better for growth and reproduction so the population increases again
• HOW INTERSPECIFIC COMPETITION AFFECTS POPULATION SIZE: 1

  1. Interspecific competition between 2 species means resources available to both populations are reduced. this means that both populations will have a limited amount of food so will have less energy for growth and reproduction so population sizes both decrease
  2. However, when populations of 2 species are in competition one will normally have a competitive advantage over the other and will outcompete the other species. The population of this species will gradually increase while the other population will diminish
• HOW INTERSPECIFIC COMPETITION AFFECTS POPULATION SIZE: 2

  3. if conditions remain the same, this will lead to the complete removal of one species. This is known as the competitive exclusion principle

  • where two species are competing for limited resources, the one that uses these resources most effectively will ultimately eliminate the other ie. no two species can occupy the same niche indefinitely when resources are limited.
• COMPETITIVE EXCLUSION: Where two species are competing for limited resources, the one that uses these resources most effectively will ultimately eliminate the other i.e no two species can occupy the same niche indefinitely when resources are limited.

  • No two species can occupy the same niche if resources are limiting, one will be better adapted.
• COMPETITIVE EXCLUSION / NICHE

  If a species looks like it shares the same niche, there will be subtle differences:

  • One more active in day/night
  • Active in different seasons
  • One lives on upper leaf, one lower
• EFFECT OF PREDATOR-PREY (PREDATION) RELATIONSHIP ON POPULATION SIZE

  1. Prey population size increases
  2. more food for predators
  3. predators eat prey
  4. predator population increases
  5. more prey eaten
  6. prey population size falls
  7. food becomes limited for predators
  8. predator population size decreases
  9. allows prey population to recover

  • other factors als affecf predator-prey relationships eg. Food availability for prey

  
• PREDATION: when one organism is consumed by another, prey eaten by predator. Prey population drops, but is usually never extinct.
• HOW DOES ONE SPECIES OUTCOMPETE THE OTHER SPECIES?

  1. Better at obtaining food
  2. faster metabolism, using the food and digesting more easily
  3. growing faster
  4. reproduce faster
• 2 TYPES OF POPULATION GROWTH

  1. Exponential (unrestricted) growth
  2. logistic (restricted) growth

  
• THE GROWTH AND SIZE OF HUMAN POPULATIONS

  • the human population has doubled in less than 50 years and now totals over 7 billion
  • the basic factors that affect the growth and size of human populations are the birth rate and the death rate
  • it’s the balance between these two factors that determines whether a human population increases, decreases or remains the same
• REASONS FOR WORLD POPULATION INCREASE:

  • better healthcare so more babies survive to reproductive age
  • better sanitation so people are living longer
  • living conditions increase
• REASONS FOR INDIVIDUAL POPULATION INCREASE:

  • birth rate
  • death rate
  • migration
  • immigration - join
  • emigration - leave
• CALCULATING POPULATION GROWTH

  POPULATION GROWTH = (births + immigration) - (deaths + emigration)

  % POPULATION GROWTH RATE = (population change during the period / population at the start of the period) x 100 (in period of time)
• POPULATION PYRAMIDS

  1.STABLE POPULATION - where the birth rate and death rate are in balance and so there’s no increase or decrease in the population size

  
• POPULATION PYRAMIDS

  2. INCREASING POPULATION - where there’s a high birth rate, giving a wider base to the population pyramid (compared to a stable population) and fewer older people, giving a narrower apex to the pyramid. This type of population is typical of economically less developed countries.

  
• POPULATION PYRAMIDS

  3. DECREASING POPULATION - where theres a lower birth rate (narrower base of the population pyramid) and a lower mortality rate leading to more elderly people (wider apex to pyramid). This type of population occurs in certain economically developed countries eg. Japan