Understanding ecology

Ecology is the study of interactions between living things and their environment, so there are two important questions we need to be able to answer. How do we decide what is living and what is environment or non-living? Once we know that, we need to find out what kind of living things we are talking about – how do we name living things? Scientists have standard systems/processes to answer each of these questions.

What makes something living?

To decide if something is living or non-living, scientists use a list of seven requirements called life processes. Often, life processes are carried out in different ways depending on what a living thing is (for example, plants versus animals) or where it lives (under water versus on land). The seven requirements are summarised using the mnemonic MRS C GREN.

• Movement: Living things can move. Even living things that seem to stay in one place (like plants) can turn to face the Sun or open and close their flowers.
• Respiration: Respiration means that living things can convert energy to support their needs. They can change things like sunlight, food or air to a different kind of energy to power the other processes.
• Sensitivity: Living things can respond to changes in the environment they live in. Some living things are very sensitive. In ecology, these are called indicator species. This means they can tell scientists whether the environment they live in is a healthy one.
• Circulation/Control: All living things can move energy or resources around within their ‘bodies’ (circulation), and this movement is kept under close control in response to changes in the environment and inside the living thing. This control process is called homeostasis.
• Growth: All living things grow. Even very small living things made of a single cell grow bigger, especially for the next requirement.
• Reproduction: Living things can reproduce to make a new, separate lifeform. Different forms of reproduction range from splitting in two (single cells), to making seeds (plants), laying eggs (birds, fish and lizards) or having live young (humans and many other animals).
• Excretion: Excretion means that living things can get rid of waste that is produced from converting energy. Every time you breathe out, you are excreting waste from your body!
• Nutrition: All living things need to consume some kind of food to power their energy conversion (respiration). Humans need to eat food made from other living things, but plants can absorb nutrition from their environment.

How do scientists name living things?

Here in Aotearoa New Zealand, animals and other living things can have common names in te reo Māori or English. These are useful for everyday life, but scientists have a special system of naming living things (called taxonomic classification).

How does it work?

There are seven layers of taxonomic classification. In the first two layers, living things are split into groups based on how they are different. After that, they are split into smaller groups based on how they are the same. Each new layer divides up the previous layer into smaller and smaller groups. The last two groups are the most specific and provide a scientific name for individual living things. This is important because one common name might refer to many living things that are scientifically different. To illustrate these layers, we can compare ourselves (humans) with kōura (New Zealand’s freshwater crayfish).

• Kingdom: There are six kingdoms. Three are for living things that are so small you can’t see them (Archaebacteria, Eubacteria, Protista). The other three are for fungi (mushrooms and mould), plants and animals (humans and kōura).
• Phylum: This layer divides living things based on different body plans. Humans belong to the phylum Chordata, which means we have a spinal cord. The kōura’s hard outer shell puts them in the phylum Arthropoda – bodies with a hard, outer covering.
• Class: This is where bodies and behaviours start being classed by ‘same’ rather than ‘different’. Humans are in the class Mammalia. We are the same as other mammals because we have warm blood and feed milk to our young. Kōura are in the class Malacostraca which means ‘soft shell.’ This is because, as they grow, kōura and all animals in this class lose their outer hard shell and have a soft, fresh shell underneath (called moulting).
• Order: Our order is Primates, which means we are descended from animals that lived in trees. Kōura are in the order Decapoda, which means ‘10-footed’.
• Family: Our family is Hominidae – we walk upright on two legs. Kōura are in the family Parastacidae, which includes all freshwater crayfish in the southern hemisphere.
• Genus: Our genus is Homo, which includes upright animals with large brains. Kōura are in the genus Paranephrops, which includes only freshwater crayfish found in Aotearoa New Zealand
• Species: Our species is sapiens. Humans are the only currently surviving species from the Homo genus. Kōura have two species – P. planifrons is found in the North Island, Nelson, Marlborough and the West Coast of the South Island, and P. zealandicus is found in the rest of the South Island and around Stewart Island.