An ecosystem1 consists of all of the organisms living within an area and the interactions between them and the physical environment.
All ecosystems, whether they are marine, freshwater or located in native2 bush, involve the transfer of energy. Energy flows into an ecosystem usually via sunlight. This light energy3 is used in a process called photosynthesis4, allowing plant matter5 (flora6) to grow. Flora then becomes a food source for birds, animals and insects. This transfer of energy continues as feeding relationships occur between plants and animals.
Mutualism
Native birds interacting with the flora in our ecosystems7 have a mutualistic relationship – that is, they both benefit from the relationship. While the bird receives nectar8 or fruit (in the form of berries) from the tree it visits, the tree benefits by having another organism9 carry out the process of pollination or seed dispersal. Many native trees cannot perform these processes without the intervention of birds.
Birds are the primary pollinators and seed10 dispersers in New Zealand native bush.
Pollination
Pollination is the process where pollen11 is transferred within and between plants enabling fertilisation12 and reproduction.
Bees, wasps, butterflies and (most importantly in New Zealand) birds act as pollinators. These organisms carry pollen grains from the anther13 to the receptive part (stigma14) of the plant to allow pollination15 to occur.
Flax (Phormium tenax), kōwhai (Sophora microphylla), northern and southern rātā (Metrosideros robusta and Metrosideros umbellate) and tree fuchsia (Fuchsia excorticata) are New Zealand native trees all pollinated by birds. Our native birds are attracted to the flowers of these trees and carry pollen from flower to flower on their beaks as they seek nectar, pollinating flora as they move.
In New Zealand, birds are important pollinators. The honeyeater family16 consisting of tūī (Prosthermadera novaeseelandiae), bellbirds (Anthornis melanura) and silvereyes (Zosterops lateralis) perform the majority of pollination by all birds in our native bush. Two native species17 of mistletoe (Peraxilla spp.) require the finely refined beaks of tūī or bellbirds to tweak open their flowers and allow pollination to occur.
Nature of science
Science is a process of trying to figure out how the world works by making careful observations and then making sense of these observations. Scientists have used this knowledge to inform their understanding of ecosystems and the interactions between species within these systems.
Seed dispersal
Over 70% of plants in our woody forest in New Zealand have fleshy fruit. Many seeds located within these fruits have coats that must be weakened by chemicals18 as they pass through the digestive system19 of another organism.
Native plants are dependent on birds for successful seed dispersal20 and regeneration21. Once a seed has passed through the digestive22 tract of a bird, it will often be dropped far away from the host23 tree’s location, enabling the tree to potentially colonise a new area. As many of our native birds are now confined to small predator-proof mainland sites or offshore islands, what might the future hold for our native flora, which is so dependent on this process?
In New Zealand forests, only 12 species of bird have been responsible for the majority of tree seed dispersal, but many are now extinct:
- Extinct – piopio (Turnagra capensis), 2 species of moa with small gizzard stones (Euryapteryx spp.), huia (Heteralocha acutirostris)
- Confined to predator-proof mainland sites or offshore islands – saddleback (Philesturnus carunculatus), hihi (Notiomystis cincta), kōkako (Callaeas cinerea), whitehead (Mohoua albicilla)
- Present on the mainland – tūī (Prosthermadera novaeseelandiae), bellbird (Anthornis melanura), kererū (Hemiphaga novaeseelandiae), weka (Gallirallus australis).
The importance of fruit size
Trees that produce the largest fruit (>14mm diameter) almost solely rely on the kererū for seed dispersal. These trees include miro (Prumnopitys ferruginea), pūriri (Vitex lucens), tawa (Beilschmiedia tawa) and taraire (Beilschmiedia tarairi). Within any species, there is variation, and on any given tree, there will be a variety of fruit sizes along with variation in the size and gape24 of a bird’s beak. This factor will allow the smaller tūī and bellbird to disperse some of the seeds from these trees.
As the weka is a flightless bird, it can only scavenge the fruit that has fallen from the tree and could not cover the same distance that a bird of flight would be able to. Therefore the 3 keystone species25 for seed dispersal in New Zealand are the kererū, tūī and bellbird.
New Zealand native birds have a key role in the pollination and seed dispersal of our native flora. Birds are essential to ensure the future of our native bush ecosystem in generations to come.
Activity idea
In the activity New Zealand bush ecosystems students build a food web that represents the New Zealand bush ecosystem.
Related content
Find about more about pollination and fertilisation.
The articles Flower parts and Te haenga me te ruinga o te kākano ❘ Pollination and seed dispersal have helpful background information about the plant parts and their purposes.
Find out about some of the research New Zealand scientists are doing to investigate the effect the decline of native birds has on flowers that rely on them for pollination.
Useful links
See the biodiversity section on the Ministry for the Environment website.
- ecosystem: An interacting system including the biological, physical, and chemical relationships between a community of organisms and the environment they live in.
- native: A species that lives naturally in a country, as opposed to species that have been introduced by the activity of humans.
- light energy: Electromagnetic radiation, particularly radiation of a wavelength that is visible to the human eye.
- photosynthesis: A process that uses the energy from sunlight to convert carbon dioxide and water into carbohydrates, releasing oxygen as a byproduct. Photosynthesis occurs in the green parts of plants, in algae and in some microorganisms.
- matter: The basic structural component of all things that have mass and volume.
- flora: A flora (with a small f) refers to the plant life occurring in a particular region. A Flora (with a capital F) refers to a book or other work that describes and identifies a flora.
- ecosystem: An interacting system including the biological, physical, and chemical relationships between a community of organisms and the environment they live in.
- nectar: A sugary liquid found in many flowers, made and stored in a nectary. Used to attract animals, which eat it and accidentally collect or deposit pollen at the same time.
- organism: A living thing.
- seed: 1. Part of the sexual reproduction of angiosperms (flowering plants) and gymnosperms (cone plants). Contains an embryo and its food store, which creates a new plant when conditions are right. 2. Offspring or progeny.
- pollen: Dust-like grains that contain male sex cells (gametes) of flowering plants (angiosperms) and cone plants (gymnosperms). Pollen is made on the anthers of flowering plants.
- fertilisation: (Reproduction) The joining of male and female sex cells (gametes), resulting in combining genetic material.
- anther: Contains the pollen sacs of a plant and is the region where pollen is produced.
- stigma: Part of the carpel – the female reproductive organ of a flower. During pollination, pollen from a male flower part (anther) is transferred to the sticky female stigma.
- pollination: The transfer of pollen grains from the anther to the part of the plant containing the ovules. This process is necessary for fertilisation and reproduction of the plant.
- family: A classification grouping that ranks above genus and below order (kingdom > phylum > class > order > family > genus > species).
- species: (Abbreviation sp. or spp.) A division used in the Linnean system of classification or taxonomy. A group of living organisms that can interbreed to produce viable offspring.
- chemicals: Everything is made up of chemicals. All matter (anything made of atoms) can be called chemicals. They can be in any form – liquid, solid or gas. Chemicals can be a pure substance or a mixture.
- digestive system: The group of organs that are involved in the breakdown of food in the body, which includes the stomach and intestines.
- dispersal: Movement of an organism to a new place. Seeds in plants and spores in ferns and fungi help dispersal by floating on the wind to new habitats. This allows stationary species to colonise new areas.
- regeneration: The process of ecological restoration, which provides conditions to build up populations of native flora and fauna. The focus can be on an individual species or widened to include an entire ecosystem.
In biology, the process by which some organisms replace or restore lost or amputated body parts. - digestive system: The group of organs that are involved in the breakdown of food in the body, which includes the stomach and intestines.
- host: An organism that contains a parasite or other dependent organism. Hosts usually provide the dependent organism with food and shelter.
- gape: A widely open mouth or beak.
- keystone species: A species that has a greater impact on the community of organisms in an ecosystem than you would expect in relation to its abundance. The removal of a keystone species often has a dramatic effect on the ecosystem.