4.1 ~ Species, communities and ecosystems

Species

Species

• Fertile offspring denotes that they can, in turn, also inbreed and pass on their genes

• If members of two closely related species do interbreed and produce offspring, the hybrids will be infertile/ sterile

• This is because both parents have different numbers of chromosomes

  • Even if the number of chromosomes happen to be the same, the DNA is usually too different and so fertilisation of gametes is not possible

Productive isolation

• A barrier to reproduction due to geographical barriers

• Temporal isolation

  • Mating seasons don’t coincide

• Ecological isolation

  • Live in diff- habitats

• Behavioural isolation

  • Don’t know the other’s mating ritual

• If organisms can still functionally interbreed, they are still considered the same species, but are regarded as different populations

Community

• Group of populations that are living and interacting in the same area

• All organisms are dependent on interactions with members of other species for survival

  • E.g. lion depends on the availability of gazelle

• Communities also include plants and microbes and hence involve thousands of species

Predator-prey relationships

• Another example of a relationship within a community

• The changes in numbers in a predator will lead to a change in the numbers of prey (vice-versa)

  • As the numbers of preys increase, there is more food available to sustain more predators, so predator numbers increase

  • As predator numbers increase, they eat more prey; number of prey decreases (predator then decreases accordingly)

  • As predator numbers decrease, prey can begin to repopulate and so their numbers increase and the whole cycle starts again

Ecosystem

• An ecosystem and the organisms that it can sustain is influenced by abiotic (non-living) factors

  • Rainfall, temperature, pH of water/soil, wind, humidity

Living organisms

Species have either an autotrophic or heterotrophic method of nutrition ( a few species have both methods)

Detritivores

• Obtain their nutrients from detritus (waste or other organic debris)

• Includes skin and hair shed from humans, feathers from birds, leaves and flowers from plants

• Obtain these nutrients via internal digestion

  • They have an internal digestive tract wherein their food is broken down

• E.g. dung beetles, earthworms

Saprotrophs

• Obtain their nutrients from dead organisms through external digestion

• Live on or in non-living organic matter

• Secrete digestive enzymes onto the organic matter and absorb the products of digestion

• Unlike most heterotrophs, saprotrophs are not consumers as they do not ingest food

  • Digestion is external as enzymes are secreted; external digestion

• Essential for nutrient cycling which is essential for ecological sustainability

• E.g. bacteria or fungi

Nutrient cycling

• The supply of nutrients is limited and therefore ecosystems constantly recycle the nutrients between organisms

• Nutrient cycling: helps to move organic molecules and minerals through the food chain and back into the soil where they can be taken up by plants to re-enter the food chain

• Unlike nutrients, energy cannot be recycled in an ecosystem and must be constantly supplied

• For most ecosystems, this energy comes from the sun

  • Photoautotrophs synthesise organic compounds from sunlight which lay the foundations for an ecosystem

• Some ecosystems e.g. those in the deep ocean, cannot rely on sunlight for energy

  • Chemoautotrophs synthesize organic compounds using chemical energy

Nutrients and the food chain

• If conditions are sustainable, those nutrients can be recycled almost indefinitely

• Heterotrophs ingest other organisms to gain organic forms of nutrients

  • These are transferred along the food chain

• Autotrophs synthesise organic compounds from simple inorganic nutrients they obtain from the abiotic environment

  • E.g. CO2 breaks down glucose

• Saprotrophs breakdown organic nutrients to gain energy and in the process release nutrients back into inorganic molecules

Sustainability

• Sustainable = able to continue indefinitely

• Requirements of sustainable ecosystems

  • Nutrient availability

  • Detoxification of waste

  • Energy availability

• As long as an ecosystem has sufficient energy and nutrient cycling, it can sustain itself for a very long time

  • Human activities that involve using resources faster than they can be replenished are threatening many diff-ecosystems, including some that have existed for millions of years

Meocosms

• Small, closed-off experimental systems set up as ecological experiments

• Can be used to test effects of varying certain conditions on ecosystem stability as well as the sustainability of ecosystems

Chi association

• In an ecosystem, it is common for multiple organisms to occupy the same habitat

• As such, it follows that they may or may not influence each other

  • i.e. they are dependent or independent of each other

• Abiotic factors may also influence the type and number of organisms there are

• Quadrats are useful tools for sampling areas of interest when investigating ecosystems

  • Usually square but can come in a number of shapes