Biosecurity and Ecosystem Functioning

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Biosecurity and Ecosystem Functioning
Jacqueline Beggs University of Auckland
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Understanding impacts

• Which invaders are likely to exert large effects?
• Which communities are likely to suffer impacts?
• How do these impacts develop?
• Competition
• Predation/Herbivory
• Ecosystem processes

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Ecosystem functioning

• Energy flow
• Water cycling
• Nutrient cycling
• Succession
• Evolution

Source Naeem et al., (1999)
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How do invasive species affect ecosystem
functioning?

• Nutrient cycling
• International studies
• Honeydew beech forests/wasps
• Succession
• Argentine ants
• Crazy ants

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Nutrient cycling
Wardle et. al. 2004

• Terrestrial ecosystems consist of interacting
  above- and below-ground systems
• Both positive and negative feedbacks, depending
  on context (e.g. fertility of system) (Wardle et.
  al. 2004)

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Invasive spp. impact on nutrient cycling

• Invasive plants alter root-associated biota (e.g.
  Klironomos 2002) (direct)
• Invader alters quantity and quality of resource
  inputs to soil decomposers (indirect)

• fire tree (Morella faya) invasion into N limited
  Meterosideros in Hawaii
• ? 4x increase in soil N and increase in ecosystem
  productivity (Vitousek 1989)

www.hawcc.hawaii.edu
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Honeydew beech forest

• 1 million ha
• Infested with endemic scale insects
• 15 NZs native forest

Honeydew is food source for many native organisms
Beggs 2001 Biological Conservation
Does honeydew influence nutrient cycling?
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(No Transcript)
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Decomposition Rates

• Leaf litter decomposes slower in honeydew sites

Dominic Hartnett, unpubl. data
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Succession

• Invasion of South African shrublands (fynbos) by
  pines Argentine ants

• Change in fire regime
• Disruption of seed dispersal mutualism
• Shift in composition of plant community
• Christian (Nature 2001)

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• Almost all fynbos plants are dependent on fire
  for successful reproduction
• Introduced plants (e.g.Pinus) ? fires hotter
  more frequent

Burned fynbos on Devil's Peak
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• 30 of flora has seeds dispersed by ants
• buried seeds safe from fire/rodents

Leucospermum truncatulum
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Large seeds

• Some native ant species disperse large and small
  seeded plants
• These ant species are excluded by Argentine ants
• Remaining native ants only disperse small seeds

Dispersed
Consumed
Small seeds
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• Pre-fire adult density of Proteaceae taxa did not
  differ between invaded and uninvaded sites

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Crabbiest place on Earth

• Endemic red land crab
• 1 crab m-2 in rainforest
• omnivorous diet (leaves,
• fruits, seeds, seedlings)

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Yellow crazy ant invasion

• Arrived 70 years ago
• No significant impact until 6 years ago

Anaplolepis gracilipes
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Impact of the Crazy Ant
Populations of the red crab have been severely
reduced in number, and in some areas, eliminated
by the crazy ant.
From ODowd et al., (2003) Ecol. Lett. 6 812-817
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Effects on Succession

• Litter and seedling recruitment altered in the
  near-absence of crabs

From ODowd et al., (2003)
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Effects on Succession
Red crabs maintain an open understorey in the
forests through foraging of seeds and seedlings
Crazy ants ? few crabs ? change in plant
community
From ODowd et al., (2003)
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UNESCOSCOPE (Scientific Committee on Problems of
the Environment)IUBS (International Union of
Biological Science)

• Phase I ? GISP
• Phase II Science Plan (2002)
• discovering biodiversity and predicting its
  changes
• assessing impacts of biodiversity changes on
  ecosystem functioning and services, and
• developing the science of the conservation and
  sustainable use of biodiversity.

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Conclusions

• Biodiversity plays a major role in ecosystem
  functioning
• Disruption of biodiversity via invasive species
  can therefore affect ecosystem functioning
• We have limited knowledge of how NZ ecosystems
  work
• Critical that we link with international research
  to evaluate risk