Interaction between top-down and bottom-up control in marine food webs.
Climate change and resource exploitation have been shown to modify the importance of bottom-up and top-down forces in ecosystems. However, the resulting pattern of trophic control in complex food webs is an emergent property of the system and thus unintuitive. We develop a statistical nondeterministic model, capable of modeling complex patterns of trophic control for the heavily impacted North Sea ecosystem. The model is driven solely by fishing mortality and climatic variables and based on time-series data covering >40 y for six plankton and eight fish groups along with one bird group (>20 y). Simulations show the outstanding importance of top-down exploitation pressure for the dynamics of fish populations. Whereas fishing effects on predators indirectly altered plankton abundance, bottom-up climatic processes dominate plankton dynamics. Importantly, we show planktivorous fish to have a central role in the North Sea food web initiating complex cascading effects across and between trophic levels. Our linked model integrates bottom-up and top-down effects and is able to simulate complex long-term changes in ecosystem components under a combination of stressor scenarios. Our results suggest that in marine ecosystems, pathways for bottom-up and top-down forces are not necessarily mutually exclusive and together can lead to the emergence of complex patterns of control.
Centre for Environment, Fisheries and Aquaculture Science, Lowestoft Laboratory, Lowestoft, Suffolk NR33 0HT, United Kingdom.
Christopher Philip
CP
Lynam
Instituto Español de Oceanografía, Centro Oceanográfico de Cádiz, E-11006 Cádiz, Andalusia, Spain.|Centre for Ecological and Evolutionary Synthesis, Department of Biosciences, University of Oslo, NO-0316 Oslo, Norway.
Marcos
M
Llope
Institute of Hydrobiology and Fisheries Sciences, University of Hamburg, 22767 Hamburg, Germany.
Christian
C
Möllmann
Sir Alister Hardy Foundation for Ocean Science, The Laboratory, Citadel Hill, Plymouth PL1 2PB, United Kingdom.
Pierre
P
Helaouët
AquaTT, Dublin 8, Ireland.
Georgia Anne
GA
Bayliss-Brown
Centre for Ecological and Evolutionary Synthesis, Department of Biosciences, University of Oslo, NO-0316 Oslo, Norway; n.c.stenseth@ibv.uio.no.|Flødevigen Marine Research Station, Institute of Marine Research, NO-4817 His, Norway.|Centre for Coastal Research, University of Agder, 4604 Kristiansand, Norway.
Nils C
NC
Stenseth
D000818:Animals; D018533:Biomass; D001717:Birds / Q000502:physiology; D057231:Climate Change; D017753:Ecosystem; D005399:Fishes / Q000502:physiology; D020387:Food Chain; D015233:Models, Statistical; D009659:North Sea; D010933:Plankton; D011157:Population Dynamics / Q000706:statistics & numerical data; D011235:Predatory Behavior; D012623:Seawater
ecosystem modeling; marine food web functioning; regime shifts; trophic control; wasp-waist