Tag Archives: invasive

The birds and the bees in Hawaii: New study explore the effects of non-natives on ecosystem functioning

The more recent concept of monitoring restoration through ecosystem functioning has received support from scientists, but little practical study. New research by Hanna et al. (2012) studies the effects of invasive wasp species on plant pollination and fruiting in Hawaii.

Metrosideros polymorpha is an endemic flowering tree, historically pollinated by honeycreeper birds and bees. Honeycreepeer populations became threatened by predation from invasive spoecies, habitat degradation, competition and disease, causing population declines and extinctions. Following the decline of honeycreepers, and invasion of wasp species, Vespula pensylvanica, and introduction of the western honey bee, Apis mellifera, the non-native species began feeding on the nectar stores of M. polymorpha. V. pensylvanica is a non-pollinating insect; it reduces nectar availability to other wasps by defending a flower, where it stays, drinking the nectar and chasing away or hunting and eating pollinating bees. This reduces the plants fruiting success, as the wasp reduces the nectar supplies M. polymorpha produces to attract pollinators, and directly repels other insects, preventing pollination. A. mellifera, however, is known to pollinate some plants, though only those whose flower shape enables pollination transfer from the small honey bee.

Hanna et al. experimentally removed V. pensylvanica from selected sites, and recorded the effects on pollinaters and fruiting success. Visitation by pollinating insects increased, likely as predation risk decreased and nectar more available, which led to increased fruiting success. Both A. mellifera and endemic Hylaeus began visiting the flowers more often, but Hanna et al. believe they had differing effects on fruiting success. As A. mellifera visited more frequently, it would appear that they are more responsible for the increased fruiting success than Hylaeus, whose visitation rates increased less. A. mellifera could be acting as replacement pollinators following the drop in honeycreeper numbers, helping to sustain plant fruiting. Though this effect is postive for M. polymorpha, an increase in A. mellifera could increase competition with other pollinators, and may not be an effective pollinator of all plant species from which it takes nectar, especially ones which attract a less diverse range of pollinators.

This study emphasises the need to assess how species alter ecosystem functioning when forming management plans, and highlights the variability of impacts of invasive species. Hanna et al. suggest the next steps taken should be to assess wider effects of A. mellifera, and how V. penslyvanica affects pollination at different times of the season.

Hanna, C., Foote, D., Kremen, C. (2012), Invasive species management restores a plant–pollinator mutualism in Hawaii. Journal of Applied Ecology.


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One fifth of invertebrates at risk, finds new research

One fifth of all invertebrates are now considered threatened by extinction according to a report published by the Zoological Society of London last week.  As a category invertebrates are of great significance – ranging from insects to jellyfish, they make up approximately 98% of all animal species. 

Bolinopsis infundibulum, a carnivorous and phosphorescent comb jelly, NOAA

The study looked at over 12,000 species, and was completed in conjunction with the IUCN. The accuracy of the findings have been questioned by some due to the small sample size used; about 1 million invertebrate species are currently known, and studies suggest only 14% of  species have been discovered. 
As the first study of its kind, however, the report helps to give an overall idea of the status of a group that comprises almost all of Earths animals. Freshwater species were found to be particularly vulnerable, as were less mobile species. The trends revealed by these disparities will assist scientists in targeting species and areas of particular concern. Habitat loss, pollution and invasive species were listed as the top threats to species survival. Although these factors have been the subject of much concern already, clarifying their level of threat helps to form a scientific basis for future action. The results are similar to those of studies on vertebrates and plants, which also found a fifth of species to be at risk.

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