FNZ 31 - Talitridae (Crustacea: Amphipoda) - Popular Summary
Duncan, KW 1994. Talitridae (Crustacea: Amphipoda). Fauna of New Zealand 31, 128 pages.
( ISSN 0111-5383 (print), ; no. 31. ISBN 0-478-04533-6 (print) ). Published 07 Oct 1994
Amphipods are a very successful group that tend to specialise in eating low-quality food such as algal fronds and plant wastes. Their ability to thrive on such unattractive but vastly abundant material is one reason for their great success.
Most amphipod species are marine. Others are found between the tides, even in those most difficult habitats of all, on rocky and sandy beaches, buffeted by the violent forces of tide and wind in a loose and highly abrasive habitat. A number live in freshwater streams and lakes. Finally, there are a considerable number of semi-terrestrial and terrestrial forms. All the terrestrial amphipods belong to the family Talitridae, which also includes marine and semi-terrestrial species.
The terrestrial talitrids, called landhoppers, are especially interesting in being one of relative few groups of animals that have managed to occupy the land exclusively. They cannot survive in dry habitats, but are restricted to the relatively moist environments of forest and grassland litter, long pasture, and gardens. Though not as terrestrial as insects, they are abundant in the forest leaf litter of those southern lands that once made up the primeval supercontinent known as Gondwana.
Landhoppers occur naturally in New Zealand, Australia, the Pacific Islands, the Subantarctic Islands, Africa, India, Southeast Asia, Indonesia, Japan, and Central America. They are invading many areas where they are not found naturally, including South and North America, western Eurasia, and the United Kingdom.
In appearance they are much like any other amphipod, the sideways-flattened body looking as though it should topple over whenever they walk. They are very similar to their close relatives the sandhoppers and beach fleas, differing in having much less strongly developed bodies and in being smoother, usually smaller, and less spiny.
They eat dead plant material, shredding and chewing it with their specially adapted mouthparts. They may climb up grass stems or even trees in order to reach dead leaves above the ground, and are active at night. The males are usually smaller and more active than the females. Like all arthropods, they grow by a series of moults. The different species are distinguished by their colour pattern.
A sexually mature female breeds once per moult, and carries a brood of 15 or fewer large eggs throughout the intermoult period. She may have seven or more broods in her lifetime, each comprising successively larger number of eggs. The eggs are held by special brood plates under the thorax, where they are regularly tended by the mother. The hatching young look like miniature adults, and may pass through eight or so moults before becoming sexually mature. In New Zealand landhoppers live for about a year.
Twenty-six species in seven genera are recognised from New Zealand. Certain areas, such as Northland, have a more diverse fauna than elsewhere. Often several genera occur together at a single locality, while species within genera do not. Some species are very widespread on both main islands, but others are highly localised and sometimes are restricted to specialised habitats.
Certain distribution patterns may be detected, especially in relation to distance from the sea or from marine influence. Some species are restricted to a narrow zone close to the upper limit of the tide. Others inhabit a zone further away from the sea, while yet others are completely independent of the sea and may be found far inland, and at altitudes from sea level to well above the treeline. One or two species may be restricted to soils of high salinity.
Neither Cook Strait nor Foveaux Strait appear to have been barriers to the dispersal of the species. Barriers, such as they are, appear to be related to temperature and soil salinity, and to more ancient geological structures, rather than to much more recent geomorphological features.