week 2

• Ecology


  The scientific study of the abundance and distribution of organisms in relation to other organisms and their environmental conditions
• Ecology is the study of understanding natural systems and their components
• Levels of study in ecology

  • Organismal
  • Population
  • Community
  • Ecosystem
  • Biosphere
• Relationship between 2 species


  How locust numbers might be correlated with predation
• Effect of temperature on species

  The correspondence between the range of the saguaro cactus and areas where temperatures drop below freezing (0°C)
• Effect of water on a species

  The relationship between the amount of rainfall and the density of buffalo
• The intensity of the solar radiation at different latitudes
• Human evolution in response to solar radiation

  • High melanin content in skin for protection from harmful UV rays
  • Low melanin content allowing solar rays to help in vitamin D production
• Variation in the earth's temperature at different latitudes
• Global atmospheric circulation


  • Tropical forests exist mainly around the equator where it is hot and rainy
  • Deserts exist at around 30 degrees north and south where the air is hot and dry
  • Temperate forests exist around 45-55 degrees north and south
• Geographic location of terrestrial biomes
• Species Interactions (See chapter 57 Biology Brooker et al)


  • Competition
  • Predation, herbivory and parasitism
  • Mutualism and commensalism
• Competition


  • Intraspecific competition- competition within the same species
  • Interspecific competition- competition between different species
  • Exploitation competition- indirect competition for the same resource which is limited
  • Interference competition- direct interaction by physical force or intimidation
• Interspecific competition


  • Connell's experiment shows that one species of barnacle can competitively exclude another species
  • Interspecific competition between species of paramecium
• Grey squirrels v Red squirrels

  The competitive exclusion hypothesis states that two species with the same resource requirements cannot occupy the same niche
• Resource partitioning


  • Among five species of warblers feeding on the American spruce tree, each species feeds at a different height
  • Darwin's finches evolved different beaks to exploit different food types when they were in direct competition for food resources, this minimised the impact of direct competition
• Predation is a strong selective force

  • Lethality represents the probability that the interaction results in the death of the prey
  • Duration represents the length of the interaction between the consumer and the prey
• Antipredator strategies


  • Chemical defence
  • Cryptic colouration
  • Mimicry
  • Displays of intimidation
  • Fighting
  • Agility
  • Armour
  • Masting
• Evolutionary arms race


  Co-evolution
• Humans and coevolution


  • Genetic resistance to the bubonic plague (6th, 14th and 19th century) gave resistance also to the HIV virus in the 20th century
  • Antibiotic resistance in bacteria - Bacteria develop resistance to antibiotics within a few years of being exposed to it
• Plant defences


  • Mechanical defence - Thorns or spines
  • Secondary metabolites - Alkaloids, Nicotine in tobacco, Morphine in poppies, Cocaine in coca, Caffeine in coffee, Phenolics, Lignin in wood, Tannin in leaves, Terpenoids in peppermint
• Overcoming plant defences


  • Detoxification of poisons
  • Oxidation –catalysis of the harmful compound
  • Conjugation –joining the harmful compound to another molecule to create an inactive product
• Invasive species


  Predation by an invasive species - The native species have not coevolved with the invasive predator and are therefore relatively defenceless
• Humans as invaders


  European invaders to North America and Australia brought smallpox which was catastrophic for the native human populations
• Parasitism


  • One organism feeds on another but does not normally kill it outright
  • The organism taking advantage is the parasite
  • The organism being exploited is the host
  • Found in all domains of life
• Types of parasitism


  • Holoparasite - Plant that lacks chlorophyll and so is totally dependent on the host for water and nutrients
  • Hemiparasite - Plant that does photosynthesise but depends on the host for mineral nutrients and water
  • Monophagous parasite - Feeds on one or small range of host species
  • Polyphagous parasite - Feeds on many different hosts
  • Ectoparasite - Lives outside the host body
  • Endoparasite - Lives inside the host body
• Rafflesia arnoldii is a holoparasite
• Humans and parasites


  • Protozoa - Plasmodium- malaria- in the top 10 causes of mortality in low income countries, Giardia- giardiasis
  • Endoparasites - Hook worm, Tapeworm
  • Ectoparasites - Ticks, Lice
• Mutualism


  Species interactions that are beneficial to both species involved
• Mutualism


  • Pollinators and plants- transfer of pollen in exchange for a nectar meal
  • Trophic mutualism
  • Defensive mutualism
  • Dispersive mutualism
• Humans and mutualism


  • Gut bacteria that synthesise vitamin K
  • Gut bacteria ferment dietary fibre
• Commensalism


  Species interactions that are beneficial to one and neutral to the other species
• Commensalism


  • Sticky seeds get caught in animal fur and dispersed
• Human impact on the biosphere

  • Global warming - Affecting coral reefs
  • Over fishing - Affecting fish stocks
  • Habitat destruction - Mass extinctions and endangered animals
  • GM crops and monocultures - Effects not fully understood
  • Plastic pollution - Affecting wildlife
• Conservation efforts: Wildlife sanctuaries and nature reserves
• Development


  Series of changes in state of cell, tissue, organ, or organism
• Developmental process


  Underlying process that gives rise to structure and function of living organisms
• Developmental genetics


  Gene expression controls process
• How do we study development?

  Xenopus development
• Model organisms


  • Fruit fly Drosophila melanogaster
  • Nematode worm Caenorhabditis elegans
  • House mouse Mus musculus
  • Zebrafish Brachydanio rerio
  • Thale cress Arabidopsis thaliana