The fate of endozoochorously dispersed seeds - Public defence PhD

Endozoochory, or the dispersal of plant seeds via ingestion by vertebrate animals and the consecutive deposition of seeds in dung, is a widespread phenomenon in temperate grassland species. The first steps in this dispersal cycle have been extensively studied in recent decades while less is known about the next steps, or the postdispersal fate of deposited seeds. In this PhD the germination, establishment, growth and flowering of temperate grassland species was experimentally assessed through dung addition and inter- and intraspecific competition experiments. Furthermore, the role of different functional groups of dung beetles in secondary seed dispersal and dung degradation has been studied in a large-scaled multi-site experiment in different climate and biogeographic zones in the Western Palaearctic.

Transcript

1. THE FATE OF ENDOZOOCHOROUSLY DISPERSED SEEDS Tanja Milotić
2. STRUCTURE 1. Introduction Dispersal of plants Why? How? Endozoochory Secondary dispersal by dung beetles 2. Post-dispersal fate of seeds Gastrointestinal environment Dung environment Competition effects 3. The fate of dung Dung beetle assemblages and functional groups Dung removal Secondary seed dispersal 4. Conclusions Costs and benefits of endozoochory Functional diversity in ecosystems
3. STRUCTURE 1. Introduction Dispersal of plants Why? How? Endozoochory Secondary dispersal by dung beetles 2. Post-dispersal fate of seeds Gastrointestinal environment Dung environment Competition effects 3. The fate of dung Dung beetle assemblages and functional groups Dung removal Secondary seed dispersal 4. Conclusions Costs and benefits of endozoochory Functional diversity in ecosystems
4. STRUCTURE 1. Introduction Dispersal of plants Why? How? Endozoochory Secondary dispersal by dung beetles 2. Post-dispersal fate of seeds Gastrointestinal environment Dung environment Competition effects 3. The fate of dung Dung beetle assemblages and functional groups Dung removal Secondary seed dispersal 4. Conclusions Costs and benefits of endozoochory Functional diversity in ecosystems
5. STRUCTURE 1. Introduction Dispersal of plants Why? How? Endozoochory Secondary dispersal by dung beetles 2. Post-dispersal fate of seeds Gastrointestinal environment Dung environment Competition effects 3. The fate of dung Dung beetle assemblages and functional groups Dung removal Secondary seed dispersal 4. Conclusions Costs and benefits of endozoochory Functional diversity in ecosystems
6. 1. INTRODUCTION Vegetative clones Sexual reproduction DISPERSAL OF PLANTS
7. WHY? Reduce the risk of: predation and pests infections and diseases competition with parent plant and siblings inbreeding
8. WHY? Escape Colonization Directed dispersal
9. HOW? Wind Animals Water Plant itself ABIOTIC VECTORS BIOTIC VECTORS
10. ENDOZOOCHORY Ingestion of seeds Motion Deposition
11. ENDOZOOCHORY DISPERSERS PLANT SPECIES
12. ENDOZOOCHORY ►Widespread phenomenon ►Vegetation dynamics and succession ►Genetic diversity ►Directed dispersal ►Temperate grasslands
13. Phase II dispersal SEED DISPERSAL CYCLE Fruit production Germination Seedling establishment Growth & maturation Adult plant distribution Fruit availability Juvenile plant distribution Seedling distribution Fruit removal Seed uptake Seed transfer Seed deposition Phase I seed dispersal Post-dispersal seed fate
14. SECONDARY DISPERSAL
15. DUNG BEETLE FUNCTIONAL GROUPS dwellers tunnelers rollers Bertone et al. (2006)
16. Hortal et al. (2011) Ecology letters low high Species diversity dwellers tunnelers rollers Functional group diversity DUNG BEETLE BIOGEOGRAPHY
17. ROLE OF DUNG BEETLES IN ECOSYSTEM FUNCTIONING Dung removal for feeding and breeding ►secondary seed dispersal ►nutrient cycling ►bioturbation ►plant growth ►parasite control ►reduction of methane emission
18. EFFECTS OF THE GASTRO-INTESTINAL ENVIRONMENT Adult plant distribution Fruit availability Juvenile plant distribution Seedling distribution Seed uptake Seed transfer Seed deposition 2. POST-DISPERSAL FATE OF SEEDS
19. EFFECTS OF THE GASTRO-INTESTINAL ENVIRONMENT Mechanical treatments  mastication Combination treatment  complete gut passage Chemical treatments  digestive fluids Temperature treatment  body temperature Control treatment  unassisted dispersal x + +
20. EFFECTS OF THE GASTRO-INTESTINAL ENVIRONMENT More and faster germination of some species Less and slower germination of most species Few effects Less and slower germination of most species + + Species-dependent response to digestive processes - reduced and decelarated germination in some species - stinging nettles (Urtica dioica and U. urens) get benefits - inresponsive species travel for free
21. EFFECTS OF DUNG Adult plant distribution Fruit availability Juvenile plant distribution Seedling distribution Seed uptake Seed deposition Flowering Germination Seedling establishment Growth & maturation Post-dispersal seed fate
22. EFFECTS OF DUNG CONTROL DUNG germinability Germination and early seedling growth inhibited by dung - reduced and decelarated germination - chemical compounds of dung - physical structure - stronger effects in cattle dung - next life stages? germination timing x 4 - 14 seedling biomass = - 40-60%
23. EFFECTS OF DUNG CONTROL DUNG height flower number biomass growth rate + 4-20% +66% +60-80% +25-30% Dung becomes beneficial in later life stages - compensation for initial seed loss - stronger effects in cattle dung - decomposition stage of dung
24. COMPETITION EFFECTS High seed load in dung pats + limited surface area High density of the same species  intraspecific competition High diversity of species  interspecific competition Experiment dung vs control species combinations: 1 species 2 species in different combinations
25. COMPETITION EFFECTS germination timing DUNG INTRASPECIFIC INTERSPECIFIC + = + growth rate + = - establishment success - - - biomass + + + flower number + +/- +/-
26. COMPETITION EFFECTS ►Evidence for inter- and intraspecific competition ►High seed density  seed loss ►Positive effects of dung on growth and biomass confirmed ►Relevance of dung decomposing organisms and secondary dispersers
27. DUNG AND SEED REMOVAL BY DUNG BEETLES Adult plant distribution Fruit availability Juvenile plant distribution Seedling distribution Seed uptake Seed deposition Phase II dispersal 3. THE FATE OF DUNG
28. DUNG AND SEED REMOVAL BY DUNG BEETLES ►Multi-site experiment in 11 biogeographic zones in the Western Palaearctic ►Dung beetle assemblage ~ biogeography ►Functional diversity ~ ecosystem functions dung removal seed dispersal
29. DUNG AND SEED REMOVAL BY DUNG BEETLES ►Dung beetle sampling ►Removal of dung and seeds by - dwellers - tunnelers: large/small - rollers: large/small
30. FUNCTIONAL GROUP DISTRIBUTION
31. DUNG REMOVAL
32. SECONDARY SEED DISPERSAL ►Correlation dung – seed removal ►Seed size ►Dung type ►No effect of biogeographic region
33. COSTS AND BENEFITS OF ENDOZOOCHORY COSTS BENEFITS Gut environment seed loss no effects, or enhanced germination Dung environment reduced germination reduced seedling establishment faster growth higher biomass more flowers Competition reduced establishment more flowers higher biomass fewer flowers slower growth 4. CONCLUSIONS
34. FUNCTIONAL DIVERSITY IN ECOSYSTEMS ►Biogeographic gradients ►Rollers and tunnelers best decomposers ►Secondary seed dispersal ~ dung removal ►Role of other macro-invertebrates ►Ecosystem functioning increases with functional diversity
35. THANK YOU!