Interaction between birds and macrofauna within intertidal food webs
Sabine Horn, Camille de la Vega, Ragnhild Asmus, Philipp Schwemmer, Leonie Enners, Stefan Garthe, Harald Asmus
© Christian Höfs
Introduction
© Peter Antkowiak
Blew et al. (2015) Strong increase
Moderate increase Stable
Trend not significant Moderate decrease Strong decrease
© Birgit Hussel
© Birgit Hussel
Holistic apporach – Ecological network analysis
Ecological network analysis
Respiration
Export
Egestion
Sediment POC
Consumption Consumption
Biomass P
Efficiency
Recycling
Maturity
Activity Organization
Resilience
Diversity
Number of flows Sustainability
Objectives
• Structure and functioning of different habitats which are used by birds
• Similarities and differences
• Focus on birds
o How do birds impact the food web?
o Do changes in the bird population alter the food web structure?
North Sea
waddensea-secreteriat.de
Study site
8°50'0"E 8°50'0"E
8°40'0"E 8°40'0"E
8°30'0"E 8°30'0"E
8°20'0"E 8°20'0"E
54°40'0"N 54°40'0"N
mg Carbon per m²
Ecological network analysis
Size and activity
Total System Throughput (TST)
Flow structure
Flow Diversity (FD):
Number of interactions and evenness of flows
Effective Link-Density (ELD): Effective number of parallel pathways
Recycling
Finn Cycling Index (FCI):
Amount of recycled material
Sustainability
Degree of order Robustness
Sustainability
Efficient use energy resources (Organization), reserves of free energy to cope with perturbations (Redundancy)
Well-balanced between organization and redundancy
Sand flat Mud flat
Seagrass meadow Mussel bank Cockle field Razor clam field
Cockle field and mussel bank
• Big and active systems
• Mussel bank more complex flow structure
• Low recycling -> dependent on external imports
TST ELD FD
FCI TST
FD ELD
- FCI
Two big systems with strong reliance on phytoplankton imports
Razor clam field and mud flat
• Small system
• Simple pathways
• Efficient transfer from
phytoplankton to razor clams to gulls
FCI FD TST ELD
TST FD ELD
FCI
• Active and productive
• Simple pathways, little recycling
• Probably vulnerable to disturbances
Simple, but efficient Fragile System
Sand flat and Seagrass meadow
• Small systems with capacities of free energy
• Complex flow structure
• Parallel pathways
• High recycling
FD ELD
FCI
- TST FD
ELD FCI
- TST
Complex and stable systems with high importance for foraging birds
Summary: Habitat diversity
• All systems can be described as sustainable
• The systems differ in their features and attributes
• Habitat heterogeneity is an important trait for the functioning of the entire ecosystem
o Each habitat has a distinct role
o Habitats used differently by foraging birds
How do birds influence the intertidal food web?
Influence of birds
Impact analysis
Sediment POC
+10%
+20%
+30%
+40%
+50%
-10%
-20%
-30%
-40%
-50%
Changing bird biomass
Impact analysis
Mixed Trophic Impact
Sediment POC
+
-
-
Primary producers Benthos
Birds Detritus
Prey items Competitors Food sources of prey Competitors of prey
Bird sensitivity analysis
Decrease in bird biomass = Decrease
in stability and resistance
Size and activity
Flow structure Recycling
TST: Total System Throughput FD: Flow Diversity
ELD: Effective Link-Density FCI: Finn Cycling Index
Conclusion
• Habitats differ in their structure and functioning
o Differ also in their importance for birds
• Birds are important predators in intertidal food webs
o Included in direct and indirect pathways
o Changes in the bird population induce alterations in the food web structure
Application of results
Better implementation of mangement strategies by
taking into account relationships in ecosystem
Thank you!
© Gabriele Müller
