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

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

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

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

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

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

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

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

In-situ experiment set-up & Analysis Intraspecific 6 Intraspecific 6 contains Interspecifc 3 , 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

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)

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)

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)

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)

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

Result 3: Native, in its stronghold, can competitively overwhelm alien species b 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

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

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