19 July 2009

A tough decision for mum


NZ Fur seal
Photo by Kerry-Jayne Wilson, Lincoln University.


Pinnipeds are a widely distributed and highly diverse group of semi-aquatic marine mammals. These animals are unique in a sense that although they spend a lot of time in water, they have to come up on land to breed, moult and rest. Altogether, there are 3 families, the phocids, otariids and the odobenids. In New Zealand, we have 2 species from the Otariidae family, the New Zealand fur seal/ kekeno and the Hooker’s sea lion/ rapoko (Phocarctos hookeri).

New Zealand fur seals (Arctocephalus forsteri) were widely distributed before humans arrived. They could be found all throughout the coastlines of the North and South Island, as well as most offshore islands. However they were hunted for food by Maori, and Europeans further decimated their numbers for the pelt industry (as they did with pinnipeds throughout the world). Fortunately, due to full legal protection, their numbers are increasing and they are slowly re-colonising their former habitats.

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NZ fur seals live in a wide variety of coastal habitats, but breeding colonies (also called rookeries) occur usually on exposed, rocky, rugged shores. In 1976, M. C. Crawley and G. J. Wilson observed that nearly all rookeries have shelters from storms or big waves, and have broken and irregular terrain (see the journal Tuatara 22(1):1–28). There are also hauling grounds, where non-breeding adult males literally “hang out” in large numbers. These sites are similar to, and quite often near, established rookeries.

In 1993, Christine Ryan, Graham Hickling and Kerry-Jayne Wilson of Lincoln University investigated the breeding habitat preference of the NZ fur seals in Banks Peninsula (see Wildlife Research, 24(2): 225–235 (1997)). Their aim was to see if there were any significant differences between the breeding sites and non-breeding sites. They found out that NZ fur seals indeed chose steeper, rockier sites for breeding and suggested that these criterion be used for determining future breeding sites for conservation purposes.

Fur seals choose sites to assist in behavioural thermoregulation. This is because peak breeding season often occur during the hottest time of the year and the seals are reluctant to cool off in the sea—females have pups and males are defending territories. As fur seals are superbly adapted to the cold seas, they need crevices and rocky pools to help thermoregulate. This behavioural preference was also seen in other species of fur seals in other regions of the world.

In addition to thermoregulation, preference of steeper, rockier sites would favour pups and females in terms of safety and shelter, and also minimise harassments by humans and probably adult male fur seals.

It has been suggested that the present distribution of fur seals habitat in Banks Peninsula may also be a product from hunting in the bygone eras. Individuals that escaped sealers may have modified site preferences and, therefore, recolonisation patterns of subsequent generations. Furthermore, fur seals have natal site fidelity, which means that they return to the place where they were born to breed, and this could be a confounding factor in their preference of breeding sites.

Kerry-Jayne Wilson told me recently that there has been an increase in seal numbers and also breeding sites on Banks Peninsula since the survey was done. It would be interesting to find out if the habitat preferences observed previously are still significant for breeding animals when high densities are reached. Indeed, Christine Ryan and colleagues in their 1997 publication also pointed out that an increase in numbers may lead to breeding animals expanding into a broader range of habitat types, maybe even to those which they classified as “not suitable”.

The Department of Conservation website offers more general information about New Zealand fur seals and pinnipeds in New Zealand.

This blog post was written by postgraduate student Haojin (Jin) Tan as part of the course, Research Methods in Ecology (Ecol608).

10 July 2009

Effluent bacteria lives and escapes..... sometimes

Dairy Cows have been getting a hard time in the media with catch phrases of ‘dirty dairying’ and ‘green streams’. But are scientists testing the impacts of land based effluent application on the natural New Zealand environment? It is, after all a natural product. What harm can it really do to natural ecosystems?


Cows: "Don’t blame us! Just because you call it effluent, doesn’t mean it’s any less natural than sewage!"
Thankfully Lincoln researchers are churning out papers on the properties, uses, and effects of dairy effluent. One of the latest by Shuang Jiang, Graeme Buchan, Mike Noonan and Neil Smith of Lincoln University and Liping Pang and Murray Close of the Institute of Environmental Science & Research studied the less widely examined property of bacteria in the form of faecal coliforms. The paper “Bacterial leaching from dairy shed effluent applied to a fine sandy loam under irrigated pasture” can be read in full in the Australian Journal of Soil Research, 46(7):552–564 (2008).

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Field trials considered the influence of seasonal variation (time) and soil water content (irrigation application). Trials involved the use of Lincoln University’s 6 soil lysimeters. Lysimeters are monitoring vessels containing large cores of soil. They are used for studying hydrological cycles within soil such as infiltration, runoff, and evapo-transpiration. Researchers got down and dirty collecting effluent and pouring it over the lysimeter soil. Typical soil treatment was mimicked by spray and flood irrigation, the two methods of water irrigation commonly used in the Canterbury region, and, of course, any rain that happened to fall. Researchers then watched and waited to see what, if anything, would make its way through the 700 mm depth of soil into the collection chambers for analysis.

700 mm of soil did not prove to be a barrier to leaching. Analysis discovered that bacterial leachate could readily penetrate 700 mm when facilitated by water in the mock water irrigation treatments. Alarmingly, summer trials had leachates with similar concentrations to the original dairy effluent.



Unfortunately those green streams aren’t just a figment of the media’s imagination


However, researchers were able to draw some recommendations for effluent disposal without submitting to the pessimistic catch phrases I referred to earlier. With an understanding of the disposal area’s soil properties and consideration of water irrigation treatment and seasonal variations, the amount of bacteria transportation can be greatly altered. Specifically, flood irrigation resulted in higher bacterial leaching and effluent irrigated in dry summer conditions posed a greater threat of shallow groundwater contamination.


Beautiful green pastures under dairy effluent irrigation outperform the neighbouring sheep farm.


So, it seems that with some careful consideration of the natural environment and ecosystem, dairy farming can prevent green streams whilst recycling nutrients. With the right conditions and management, soil acts as a natural filter of bacteria from the applied effluent before leaching to groundwater. However, this is also a warning to those that have considered only the nutrient losses from their poor practice as a pathogenic bacteria may be leaching unnoticed to your water supply right now!


An example of not so careful effluent application management.


This blog post was written by postgraduate student Anastazia Raymond as part of the course, Research Methods in Ecology (Ecol608).

03 July 2009

Kānuka vs. gorse, the battle is on!

There is a struggle going on in the New Zealand forest, and it’s a battle for ultimate (plant) domination. Kānuka (Kunzea ericoides) and mānuka (Leptospermum scoparium) were the original plant species that colonised forest sites cleared by natural disturbances in New Zealand. This has changed since the introduction of many “shrubby weed species” to a situation where many cleared sites are now colonised by gorse (Ulex europaeus), broom (Cytisus scoparius), tree lupin (Lupinus arboreus) and many other adventive plant species. The nearest kānuka and mānuka are often some distance away and don’t get a chance to establish.

Jon Sullivan (Lincoln University), Peter Williams (Landcare Research) and Susan Timmins (Department of Conservation), researched three different hypotheses that they obtained from the New Zealand literature on the relationship between the naturalised shrub gorse and the native shrub kānuka.

1. Kānuka stands have a different plant species composition and greater plant species richness than gorse stands at comparable successional stages.
2. Differences between gorse and kānuka stands do not lessen over time.
3. Several native plant taxa are absent from or less common in gorse than in kānuka stands.

The research was conducted in environmentally similar sites throughout the Nelson and Wellington regions. They selected a mix of young and old gorse and kānuka sites. At these sites they recorded the presence of all native and naturalised woody species, Department of Conservation weeds, ferns, orchids and a selection of herbaceous plants; they also recorded environmental variables. The results were published in a 2007 issue of the New Zealand Journal of Ecology.

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They showed that there are many differences in the final vegetation composition of a site that establishes under gorse dominated vegetation compared to a site that establishes under kānuka dominated vegetation. For example, gorse sites tend to be absent of, or have fewer beech trees (Nothofagus spp.), orchids (e.g. Pterostylis spp.), small leaved shrubs (e.g. Coprosma, Leptecophylla, Leucopogon) and the shrub daisy Olearia rani than kānuka sites. The gorse sites also displayed lower species richness (number of species) and a higher incidence of naturalised species than the kānuka sites. These factors tended to be persistent at the older sites, suggesting that these effects are long term and therefore inferring that gorse is not a substitute for kānuka when the desire is to return the site to a “natural state.”

There are many explanations for the differences between gorse and kānuka sites. Some of the differences may be explained by biological factors such as the nitrogen fixing ability of gorse and the effect this may have on below ground micro-organisms and soil invertebrates, or this could be due to different physical site characteristics like light penetration, soil temperature or soil moisture levels. Other factors may be different bird feeding preferences and subsequent seed dispersal between gorse and kānuka sites, or the documented increase in naturalised plants invading gorse sites

This study has shown that there is a difference in plant composition between gorse and kānuka sites and therefore, as good as any forest regeneration is, there needs to be more protection for areas of kānuka in landscapes where it is scarce. Also, in such landscapes, there will be benefits for biodiversity of planting kānuka back into areas dominated by gorse if the aim is to initiate native forest regeneration. There is also a need for further research into the main effects driving the differences found in this research paper. There is still much to learn about the ecology of gorse vs. kānuka.


Glossary

Adventive a plant or animal found in an environment where that it is not native to.

DoC weeds List of weed species actively managed on Department of Conservation reserves.

Succession the series of changes that create a fully-fledged plant community, e.g. from the colonization of bare rock to the establishment of a forest

Taxa A taxonomic group i.e. a plant species, genus or family.

This blog post was written by postgraduate student Mark Parker as part of the course, Research Methods in Ecology (Ecol608).

02 July 2009

Geraniums: New New Zealand diversity

Geraniums are a common plant genus with more than 400 species worldwide. New Zealand has its own share of species with seven native species and nine introduced species. There is, however, a reasonable level of variation within some of the native species, including variants in the ultramafic Red Hills. Other species are found on the Chatham Islands (Geranium traversii) and through the Subantarctic (G. microphyllum). A DNA-based study was undertaken by Anthony Mitchell (University of Otago), Peter Heenan (Landcare Research) and Adrian Paterson (Lincoln University) of samples from all species and most variants in order to look at evolutionary relationships, time of divergence events and species status.

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In a paper published in the New Zealand Journal of Botany (47:21-31), the researchers conclude that there is low genetic variation within native New Zealand Geranium indicating that they are very closely related and the likely result of one colonising event to New Zealand. More sampling of Geranium species in South America and Australia would help to determine the likely source of these colonists. Morphological variation (like leaf shape and patterning) appeared to be a reasonable predictor of species status with plants that look different actually also being different at the molecular level. The level of differences between different populations also suggested that they may actually be at least five different species (although confirmation of this would require more detailed work). This work shows that even in reasonably well-studied groups that there are still many species to be found in New Zealand.