1. Claudia Tan Li Ying, Zeng Yiwen, Darren Yeo Chong Jinn
Alien versus Native: Ecological & behavioural interactions between two freshwater shrimps (Decapoda, Palaemonidae)
Claudia Tan Li Ying,
Zeng Yiwen,
Darren Yeo Chong Jinn
The Crustacean Society Mid-Year Meeting 2016
11th July 2016

2. Overview Study Context & Research Question Experimental Methodology
Results & Discussion
Overall Implications & Conclusion

3. Background: Alien species could spread via connecting habitats
Freshwater alien decapods: within successful invasive aquatic taxon
Wide environmental tolerance
Aggressive behaviour
Study’s Context and Research Questions

4. Background: Alien species could spread via connecting habitats
Singapore:
Alien-dominated artificial habitats connected to native strongholds in forest streams
Rural stream habitat
Open canopy
> pH 6.0
Can reach high temperatures
Alien sp. dominate
Close canopy
< pH 6.0
≈ 25 ºC
Native sp. stronghold
Forest stream habitat
Study’s Context and Research Questions

5. Macrobrachium malayanum (native)
March et al. (2002) Freshwater Biol
Tan, in prep.
Study organisms
Forest stream habitat
Rural stream habitat
Habitat partitioning may not just be due to abiotic barriers
Macrobrachium malayanum (native)
Abundant forest stream shrimp
Ecologically important
Macrobrachium nipponense (alien)
Tolerant of forest stream conditions
Absent in forest streams
Study’s Context and Research Questions

6. Research question How would the combination of:
abiotic (habitat: forest stream, rural stream) &
biotic (spp. interaction: intra-, interspecific) factors
affect species survivorship?
Study’s Context and Research Questions

7. Study site: Lorong Banir stream
Rural stream habitat
Forest stream habitat
Rural stream site: Syntopic populations found
Forest stream site: Only native species recorded
Experimental Methodology

8. In-situ experiment: Treatments
Intraspecifc (native-native)
Six treatments
Habitat type (abiotic)
Spp. interaction (biotic)
Intraspecific (alien-alien)
Interspecifc (native-alien)
Rural stream habitat
Intraspecifc (native-native)
Intraspecific (alien-alien)
Interspecifc (native-alien)
Forest stream habitat
Experimental Methodology

9. In-situ experiment set-up & Analysis
Intraspecific 6
Intraspecific 6
contains
Interspecifc
, 3
Nine replicates over three occasions
Effects (habitat type, spp. interaction) analysed with generalized linear mixed effect models
14 days
Survivorship:
% of individuals that survived
Experimental Methodology

10. Result 1: Alien species not affected by habitat type
Native M. malayanum:
Adapted to forest streams
Narrower physiological range (e.g., pH 4–6)
Alien M. nipponense:
Wider physiological range (pH 5.2–8.7)
Able to tolerate forest streams *
Yang et al. (2005) Chinese J Zoolog
Wang et al. (2006) Aquaculture
Tan, in prep
Results & Discussion (I)

11. 1. Implications: Abiotic factors alone insufficient in explaining distribution patterns
Alien M. nipponense distribution
Only in rural stream sites
Despite tolerance for forest stream conditions
Hence: Additional factors shape distribution
Implications (I)

12. Result 2: In the Rural stream site…
Matching letters: Non-significant differences between treatments a
a, b b
Survivorship in alien ≈ native
Native could hold its own in rural streams
Results & Discussion (II)

13. Winner sp./ Sp. interaction type
Result 2: Agonistic behaviour could contribute to survivorship differences
Matching letters: Non-significant differences between treatments a
a, b b
Native survivorship in inter ≈ intra
Alien survivorship in inter > intra
Agonistic behaviour differences affect costs from losing
Losing sp.
Winner sp./ Sp. interaction type
Loser Costs
Intra
Mid
Inter
Low
vs.
Hsu & Wolf (2001) Anim Behav
Hock & Huber (2007) Mar Freshwater Behav Physiol
Results & Discussion (II)

14. Implication: Abiotic & biotic factors explain alien’s advantage in rural streams
Rural stream (site of syntopy): Native < Alien
Less favourable abiotic conditions ↓ native ’s survivability
Alien ’s agonistic behaviour ↑ survivorship under interspecific conditions
Result II Implications

15. Result 3: Native, in its stronghold, can competitively overwhelm alien speciesb c
Matching letters: Non-significant differences between treatments
Survivorship in alien < native
at physiological optimum
survivorship in inter < intra
Native could lower alien survivorship by outcompeting it
Interacting abiotic & biotic factors contribute to absence in forest streams
Result III Results, Discussion & Implications

16. Implications for alien species spread
Rural stream habitat
Forest stream habitat
Need to study interactions between multiple mechanisms
Abiotic conditions mediate competitive outcomes
Affect alien species spread
Native stronghold integrity critical to ↓ alien species spread
Overall Implications & Conclusion

17. Acknowledgements Special thanks to:
Freshwater & Invasion Biology Lab, National University of Singapore
National Parks Board (Permit No.: NPRP15-083a)
Field helpers
The Crustacean Society Mid-Year Meeting 2016
11th July 2016
Acknowledgements