1. Impacts of Lake Organisms on Terrestrial Systems

2. Trophic Cascades ACROSS Ecosystems
How do organisms with complex life histories tie together aquatic & terrestrial systems?
Can these organisms cause trophic cascades across ecosystems?
Dragonflies nymphs are aquatic but adult forms are terrestrial
Nymphs are important food for fish & adults are important predators of pollinators

3. Proposed Trophic Cascade

4. Methods Katharine Ordway Preserve, Florida
4 fishless & 4 fish-filled ponds
Box-sampled dragonfly nymphs in ponds

5. Point-counted adult dragonflies
Methods
Point-counted adult dragonflies
Compared # & sizes of dragonflies present between ponds
Observed dragonflies predations & identified prey

6. Pollination
Constructed net cages, 1 with an adult dragonfly, the other without & recorded # and identities of pollinators (Hymenoptera, Diptera & Lepidoptera) that visited each cage & the # of flowers that pollinators visited
Also observed pollinators in the open around ponds at St. John’s Wort shrubs
Determined if shrubs were pollen-limited

7. Dragonfly Size & Abundance
Black = large
Grey = medium
White = small
Fish limit abundance & size distribution of dragonflies = less & smaller dragonflies near fish ponds

8. Less Pollination near Fishless Ponds
Black = Diptera
Grey = Lepidoptera
White = Hymenoptera
1st graph shows less pollinators near fishless ponds with a lot less bees (hymenoptera)
2nd graph shows shrubs near fishless ponds 2x more pollen-limited than shrubs near fish ponds

9. Trophic Cascades
Fish indirectly facilitate terrestrial plant reproduction

10. When Prey Strike Back!
What about the effects of predation on adult dragonflies (for example birds)?
What about reverse situations?

11. Implications
Conditions in aquatic ecosystems can have major effects on life cycles & reproductive success of terrestrial organisms & vice versa
Understanding interactions across ecosystems crucial for gauging effects of anthropogenic-induced change
Lakes AND surrounding terrestrial vegetation should be well protected in conservation management

12. Effects of Aquatic Insect Emergence on Terrestrial Insects via Birds
How does the interaction of birds and aquatic insects affect the abundance of terrestrial insects in a riparian deciduous forest?

13. Predictions
Predict denser bird populations in riparian zones due to aquatic insect emergence thus also causing a depression in terrestrial herbivore abundance

14. Methods
Japanese lilac dominating shrub, buds early around same time as aquatic insect emergence
6 plots, 3 in riparian area, 3 upland (200m from stream)
Same tree densities in riparian & upland plots
Lepidoptera leaf rollers dominant herbivores on lilac, important early terrestrial spring prey for many birds

15. Methods
Great Tit
Calculated visiting frequency of 3 dominant bird species to each plot
Recorded prey types of bird species
Prey types classified as
- Leaf rollers
- Other terrestrial prey
- Aquatic prey
Marsh Tit
Crowned Willow Warbler

16. Methods
Bird Exclusion Experiment: Randomly selected trees in each plot & covered some with a mesh to keep birds out others used as a control to identify effects of bird removal on abundance of leaf rollers
Used malaise trap to find abundance of flying insects (many aquatically-derived) & identified insects to order (or family) to distinguish origin then weighed to calculate biomass

17. More Riparian Insects = More Birds?
1st graph shows a significantly higher aquatic prey biomass in riparian areas
2nd graph indicates that there appears to be more bird visitation in riparian opposed to upland areas

18. Bird Diets
Shows that in upland forests birds rarely prey on emerged aquatic insects
Found predation on leaf rollers higher overall in riparian areas due to denser bird population
Activity of great tits & willow warblers much higher in riparian areas

19. Results
Aquatic insect emergence negatively & indirectly affected leaf rolling Lepidoptera larvae through forest birds
Also, they suggested that birds had a strong impact on abundance of aquatic insect population

20. Implications
Many predators (eg. birds & fish) rely on both terrestrial & aquatic prey inputs
These “outside” prey inputs can positively or negatively affect other prey populations
Nakano and Murakami 2001 PNAS 98:

21. Importance of These Studies
Human interference rapidly altering spatial patterns of habitat interfaces on a broad scale
Increasing destruction of stream banks can seriously impair energy exchange between habitats
Loss/ degradation of one habitat may have more detrimental effects on neighbouring habitats than previously thought

22. References
Knight, T. M., McCoy, M. W., Chase, J. M., McCoy, K. A., Holt, R. D. (2005). Trophic cascades across ecosystems. Nature 473,
Murakami, M., Nakano, S. (2002) Indirect effect of aquatic insect emergence on a terrestrial insect population through predation by birds. Ecology Letters 5,
Nakano, S. & Murakami, M. (2001). Reciprocal subsidies: dynamic interdependence between terrestrial and aquatic food webs. Proceedings of the National Academy of Science USA, 98,