1. Invasive small mammals in Irish hedgerows:
trophic dynamism and modified food webs
Ian Montgomery*, James O’Neill*2, Chris Harrod*1, Sally Montgomery* & Neil Reid*
Natives
Invaders

2. Direct impacts Natives replaced by invaders
Pygmy shrew locally extirpated by greater white-toothed shrew
Wood mouse population declines in contact with bank vole

3. Impacts on biomass & trophic function
Biomass higher after invasion
>4-fold increase in insectivore biomass
Hedgerows are major source of biodiversity and ecosystem services in farmland i.e. 70% of Ireland
Biomass g/100m hedgerow
14.1 g/100m

4. ‘Zones’ of invasion
Q1. Does species replacement involve trophic niche shifts?
Stable Isotope Analyses measuring muscle δ13C and δ15N in difference Zones
Q2. Does invasion result in ‘top-down effects’?
Quantify terrestrial invertebrate diversity using pitfall trapping

5. Stable Isotope Analysis
Shrews are insectivores (highest δ15N)
Wood mice are omnivores (intermediate δ15N)
Bank voles primarily herbivores (lowest δ15N) but more omnivorous in Zone 4

6. Invertebrate community structure
Taxa richness
Abundance
Nonmetric multi-dimensional scaling (NMDS) biplots
Invasion impacts invertebrate taxa richness and abundance
Diverse range of disparate taxa effected

7. Invertebrate community structure
GLMM predicted means after removing environmental variation
Taxa less rich and less abundant in Zones 2-4
Impacted taxa account for 178 species (29%) and 10,003 individuals (65%)

8. Invertebrate ‘downsizing’
Mean invertebrate body length decreased by 41% from 9.4 to 5.5mm between Zones 1 and 4
Key taxa effected:
Carabidae
Staphylinidae
Diplopoda
Isopoda

9. Conclusions
Multiple invasion affects isotrophic position (unpredictably)
Negative top-down effects on invertebrate taxa
Greatest impact by greater white-toothed shrew
Invertebrate richness and abundance reduced by >50%
Greater white-toothed shrew replaces pygmy shrew and is 3-times its size increasing insectivory in system
Trophic cascades affecting other taxa e.g. birds?
Ecosystem services e.g. pest control, nutrient cycling and pollination may be impacted
GWTS attacks common lizard, Abbeyleix Bog
© Lill Dunne (Twitter 27/07/18)