The flatworm menace
Partula tree snails and the predator threat
Partula snails Partula conservation Euglandina

The flatworm menace

The major threat facing Partula snails today is the invasive flatworm Platydemus manokwari. This has the potential to wipe out many of the remaining tree snail species. Flatworm ecology is not only an issue for snail conservation; flatworms are fast becoming one of the most significant invasive groups. In every country new invasive flatworms are being encountered all the time, and at increasing frequency.

Some of these, like the bizarre hammer-headed Bipalium kewense are known to be predators of earthworms. The diets of most other species are not known. These flatworms have the potential to cause significant changes to ecosystems; snail predators may eliminate the large algal grazers and fungus consumers, resulting in an increase in plant disease. Earthworm predators may have a big impact on the organisms that contribute most to soil health through drawing in nutrients, changing structure and providing aeration. These are all possibilities, but at present all we know is that the predators are here. We now need to know what they are doing.

My research on Platydemus seeks to predict how significant their impact on snails will be and where they will spread. Are there parts of high islands that may remain Platydemus-free? How far across continental North America will they spread now that they have arrived in Florida? Specifically I am seeking to find out:

  • Feeding rate - how many snails do flatworms eat? We need to know how many snails and what sizes are consumed by different sized flatworms. From this we can start to calculate likely impacts. The reverse of this is also important - how many snails does a flatworm need to eat to survive and will areas with very low prey densities act as barriers to their spread?
  • Feeding preferences - will the flatworms follow prey anywhere; given a choice between hunting on the ground or up trees which do they choose? And how high up a tree will they go if alternative food is available?
  • Reproduction - how many young are produced, how often and from what age? How does prey availability affect reproduction and survival?
  • Temperature - how do different temperatures affect activity, feeding rate, reproduction and growth? What is the lowest/highest temperature for any of these?
  • Compiled by Justin Gerlach: contact


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