4.1 ~ Species, communities and ecosystems

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 en**z**ymes** 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