Download How can we use this knowledge?

How can we use this knowledge?
• We can assign a probability to the next step in the
degradation of reefs in particular areas, and take preventive
measures to prevent “ecological surprises”
plh
plc
Large
herbivores
psc
Large
carnivores
psh
Small
carnivores
Small
herbivores
pab
Architectural
builders
How can we use this knowledge?
• We can use the historical trajectories to rank reefs
along a gradient of degradation/health and
evaluate the efficacy of conservation actions
Conclusions 1
• There are general patterns and cause-effect
rules
• Do not need to monitor every particular
case
• We can use these general rules to forecast
future change and manage accordingly and
preventively
Food webs: coral reefs
Dolphins
Caribbean coral reefs - DENSEST SUBWEB
Bascompte, Melian & Sala, unpubl.
Caribbean coral reefs - SUBWEB
Bascompte, Melian & Sala, unpubl.
A
Food chains with strong
interactions are
susceptible to strong
“cascade” effects
B
C
Food chains
A
B
C
9% of trophic chains
have strong interactions
52% of top predators are
commercial species:
• Sharks
• Rays
• Groupers
• Snappers
• Jacks
Conclusions 2
• We can take present knowledge on interactions, get the
history, and make predictions of the costs and benefits of
the removal or increase of particular species
• Food web models are good management tools
• No MPA anywhere has restored an ecosystem to its mature
state
• Need to know how mature ecosystems were, and prevent
the trap of the illusion of statistical significance
Is collapse inevitable?
The example of civilizations
• Gradual depletion of a resource base, often due to
mismanagement
• More rapid loss of resources due to environmental
fluctuation or climatic shift
• Example: the Maya civilization collapsed in the
Terminal Classic Period during an extended
regional dry period, after reaching great
population densities and vast agricultural areas
COLLAPSE OF COMPLEX SOCIETIES
Intensive
exploitation
of local
resources
Increase in
human
population
density
Productivity
insufficient
to support
the system
Exploitation
of peripheric
resources
(subsidies)
Depletion of subsidies/
Further expansion too
costly and not profitable
No subsidies
available
Environmental
disturbance/
fluctuation
COLLAPSE
COLLAPSE OF FISHERIES
Economic
subsidies
Intensive
exploitation
of select
species
Productivity
insufficient
(fishery not
profitable)
Environmental
disturbance/
fluctuation
Increased
capacity
No other profitable
species available
Exploitation
of other
species
Fishing down
food webs
Marginal return
on investment
declines
dramatically
COLLAPSE
TRAWLING
“ … and [trawling] will not
be allowed in any waters
except where and when
allowed by His Majesty the
King by specific
authorisation, and only for
the period of time specified
…”
Carlos III, King of Spain,
Naples and Sicily
1716 - 1788
Fishing regulations in the
Catalan coast, 1752
• Because management actions depend on
what managers know at a given time and the
models that are available to them, even if a
system has exhibited cycles in the past,
managers will attribute these cycles to some
low probability event
What does it take to go forward?
+
P/B
Structure
Time (Ecosystem degradation)