New methods to assess invasive species impacts. Chris Harrod & STRIVE Aliens team

Transcription

1 New methods to assess invasive species impacts Chris Harrod & STRIVE Aliens team

2 Teamwork Kev Gallagher Kev Gallagher (PhD student) Paul McIlwaine (MPhil student) Sarah Dillon (MSc student) Brid Colhoun (MSc student) Prof Christine Maggs Dr Jaimie Dick Dr Cathy Maguire Dr Joe Caffrey (CFB) Paul McIlwaine John Coyne (CFB) Dr. Stephanie Evers (CFB) Helen Moran (CFB) Dr Jan Barrs & group (UCD) Many staff from various Regional Fisheries Boards Kenny Bodles Mark Ravinet Peter Nelle Sam Shephard Eugene O Kane Dr Sharon Doake

3 Ecological impacts of invasive species Parasitism Competition Predator-prey relationships Habitat modification Gene flow & hybridisation Shifts in ecosystem function Studied using full range of tools available to ecologists

4 New technologies Ecologists very effective on borrowing and developing techniques from other scientific fields, e.g. Shannon diversity index Information theory Non-parametric & multivariate statistics Social sciences Stable isotope analysis Isotope geochemistry

5 Stable Isotope Analysis (SIA)

6

7 You are what you eat + (x) Consumer tissues synthesised from assimilated diet e.g. C & N Consumer stable isotope ratios reflect their diet in a generally predictable manner: Assimilated diet + fractionation factor δ 13 C +1 δ 15 N +3.4 Isotopic differences between primary producers & habitats SIA allows us to track flow of energy and nutrients through a foodweb

8 δ 13 C varies according to primary production mode: you are whereyou eat

9 Behaviour of δ 13 C & δ 15 N in food webs -fractionation

10 Typical application of SIA to build a foodweb Esox Statistical comparisons: Mean (±SD) δ 15 N ( ) Zooplankton Chaoborous Perca Anguilla Rutilus Orconectes Zygoptera 1. ANOVA of individual isotopes or 2. MANOVA of δ 13 C/δ 15 N (compares centroids) 2 Asellus Mean (±SD) δ 13 C ( ) Harrod & Grey Archiv für Hydrobiologie 167:

11 EPA STRIVE: Alien invasive species in Irish water bodies WP2 Objective 1:To describe the key consequences of invasion on the function and food-web dynamics of selected freshwater ecosystems in Ireland using stable isotope analyses Objective 2:To describe the key consequencesof invasion on the community structure of selected freshwater ecosystems in Ireland. Objective 3:To examine the efficacy and consequences of measures aimed to control key invasive species including an invasive plant Lagarosiphon major, and an invasive fish Leuciscus cephalus.

12 Case studies 1. Lagarosiphon major invasion in Lough Corrib 2. Chub (Leuciscus cephalus) invasion in River Inny

13 Lagarosiphonin Lough Corrib

14 Lagarosiphonin Lough Corrib

15 Ecosystem engineer: new habitats Pre-invasion Chara-dominated Post-invasion Lagarosiphon-dominated

16 Potential to drive ecological shifts Open water Structured habitats Shifts in food web structure? Trophic overlap? Niche width? Does Lagarosiphon fuel the L. Corrib food web? Use SIA to trace Lagarosiphon-derived C & N through foodweb

17 Field surveys & n sites Habitat June 2008 August 2008 October 2008 May 2009 Native Invaded Fish surveyed using gill and fyke nets Macroinvertebrates sampled by divers n > 4000 fish processed Invertebrates, plants and fish muscle tissue for stable isotope analysis (SIA)

18 Lough Corrib: isotope food web Otter (roadkill)

19 Isotopic variation within fishes

20 Isotopic variation: native v invaded habitats Mean ±SD shown

21 Niche shifts?

22 The convex hull area occupied in δ 13 C-δ 15 N niche space represents extent of trophic diversity

23 Isotopic variation used as a measure of impact Layman et al (2007) Ecology Letters 10,

24 Variation in perchniche width Ca. 100 perch each from native and invaded habitats Centroids overlap Pillai's Trace = 0.036, d.f. = 2, 196, P = 0.02 Calculated area of δ 13 C/δ 15 N convex hulls: Native = 2.17x10 5 pixels 2 Invaded = 1.18x10 5 pixels 2 Total niche area reduced by 45 % in invasive habitats

25 Variation in roachniche width Ca. 60 roach each from native and invaded habitats Centroids distinct Pillai's Trace = 0.167, d.f. = 2, 136, P < Calculated area of δ 13 C/δ 15 N convex hulls: Native = 1.59x10 5 pixels 2 Invaded = 1.54x10 5 pixels 2 Total niche area is reduced by 4 % in invasive habitats

26 Variation in pikeniche width Ca. 20 pike each from native and invaded habitats Centroids overlap Pillai's Trace = 0.07, d.f. = 2, 44, P = Calculated area of δ 13 C/δ 15 N convex hulls: Native = 1.17x10 5 pixels 2 Invaded = 1.23x10 5 pixels 2 Total niche area is increased by 5 % in invasive habitats

27 Is Lagarosiphonfuelling the food web?

28 Is Lagarosiphonfuelling the food web? Use of Bayesian linear isotope mixing model SIAR(Stable Isotope Analysis in R: )» Parnell et al. (2010). PLOS One 5, e9672. Food sources» Chara(from both invasive and native habitats)» Lagarosiphon» Phytoplankton (from filter-feeding bivalves)*» Epiphyton (from grazing gastropods)* Consumers» Roach & perch Trophic fractionation (McCutchan et al Oikos102, )» Δ 13 C = 1.3 ±0.30,» Δ 15 N = 2.9 ±0.32 *Following Post 2002 Ecology83:

29

30 Summary Example of utility of SIA in studies of invasive species Lagarosiphon extremely abundant during study period However, little evidence that it has fuelled the fish community Level of isotopic shift in δ 13 C/δ 15 N centroid differs between species Most marked in roach Associated with reduced niche diversity in perch No similar shift in roach & pike Other consequences of Lagarosiphon invasion not reported here: Marked shift in fish size structure in Lagarosiphon Shifts in shape and reduced growth in perch Increased abundance of epiphytic invertebrates Dense aggregations of Zebra mussels

31 Acknowledgements EPA for funding under STRIVE CFB & Regional Fisheries Board staff Dr Alice Wemaere, EPA

32