May we expect “granivory” by isopods also in their original terrestrial biotopes

of Mediterranean region?1, 2S. Koprdová, 1P. Saska, 1A. Honěk, 1Z. Martinková

1Crop Research Institute, Department of Entomology, Prague, Czech Republic2Czech University of Life Sciences, Faculty of Agrobiology, Food and Natural Resources,

Department of Agroecology and Biometeorology, Prague, Czech Republic

WHY?• recent studies – terrestrial isopods from central Europe

are granivorous!!!• important seed and seedling predators together with

carabid beetles and slugs

• soil moisture is probably the main factor affecting the distribution and abundance of isopods (Heely 1941/1942, Warburg et. al 1984)

May we expect “granivory” by isopods also in their original terrestrial biotopes

of Mediterranean region?

Matter of this lecture

• to introduce terrestrial isopods (Crustacea: Isopoda: Oniscoidea) and to discuss their relative importance in their original biotopes

• model species (Taraxacum officinale) in Czech Republic- relative importance of the main invertebrate

predator groups in seed and seedling predation

- variation in predation between sites (“moist“ x “dry“)

Crustacea: Isopoda: Oniscoidea• app. 3600 members of Oniscoidea worldwide

• 42 species in Czech Republic

• 213 species of Oniscoidea in Greece (137 of which are endemic)

• ranging from tropics at rain forests to desert

• terrestrial isopods are considered detritivores (Sutton 1972, Hassall & Rushton 1982, Zimmer 2002)

• granivory established recently (Saska 2008)!!!

Armadillidium vulgare x Capsella bursa-pastoris

Hemilepistus reaumurii, locality near Kairouan – Tunisia

Halocnemum strobilaceum (Amaranthaceae)

DandelionTaraxacum officinale Weber ex Wiggers

Established facts:• Seed produced during the

whole vegetative season• Mortality c. 95 % before

reaching stage of 1st true leaf• Important seed predators are

ground beetles

Overall seed predation

• Two sites ("moist" vs. "dry") situated c. 300 m apart placed

• Pairs of c. 25 cm2 plots, one protected from and the other open to invertebrate predation

• Ten replicates at each site exposed in monthly intervals from April to October

• Seeds germinated after rainfall counted

Overall seed predation

• About 70 % of seeds germinated on plots protected from predation and 30 % on plots exposed to seed predation

• This means that about 60 % of germinable seeds was removed by seed predators before natural germination occured

Average percentage germination (±SE) in arenas “protected from“ and “exposed to“ predators at “moist“ and “dry“ sites – combined

data for 2005 and 2006

Seed predators - ground beetles

Dominant carabid genera (pitfall traps):

Amara Harpalus Ophonus Pseudoophonus (10 spp. in total)

- taxonomic composition similar at both sites

photo by P. Klimeš

Seed predators - isopods

Dominant (pitfall traps):

Armadillidium vulgare

Trachelipus rathkii

- taxonomic composition similar at both sites

Photo by P. Čáp

Seed-feeding established only recently!!!

Seed predators - slugs

Dominant (plasticine trays): Arion lusitanicus

-consumption of plasticine higher at moist site

-large proportion of seeds eaten was excreted apparently undigested

Preferred food: living plants in all stages of development, dead plant remnants!Invaded the territory only in 1993!

Relative importance of seed predators

0.0

0.1

0.2

0.3

0.4

Ground beetles Isopoda Slugs

Con

sum

ptio

n (s

eeds

mg

-1 d

-1)

*

**

***

Consumption in laboratory recalculated per unit of dry body mass

* Average for five top consumer species in no-choice experiments, 25 °C** No-choice experiments, 20 °C*** No-choice experiments at 15 °C

Seedling predation - methodsExposing seedlings to predation

Measuring feeding of slugs

Recording longevity of naturally established seedlings

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0.1

0.2

Ground beetles Isopoda Slugs

Co

nsum

ptio

n (s

ee

dlin

gs

mg

-1d

-1)

Relative importance of seedling predators

Consumption recalculated per unit of dry body mass

Site i – moistSite ii - dry

Seedling survival negatively correlated with slug abundance

Seed fate

survived

seedling predation

seed predation

non-germinable

Moist Dry Site

Conclusions

• Overall seed predation varied little between sites

• Most important ground beetles

• Slugs may eat seeds which remain germinable after gut passage

• Overall seedling predation varied between sites (moisture)

• Slugs are most important seedling predators

• Isopods are of intermediate importance (both seeds and seedlings)

Thank you for your Thank you for your attentionattention

koprdova@vurv.czkoprdova@vurv.cz

photo: MUDr. Pavel Schlemmer