Trophic Downgrading of Planet Earth

Sofia Olivero Lora

November 29, 2012

Estes et al. 2011

Mass extinction events

(http://evolution.berkeley.edu)

(http://evolution.berkeley.edu)

6th mass extinction

• Early to middle stages

• Differences

– Homo sapiens

– Loos larger-bodied animals in general, apex consumers in particular

• Global occurrence

Apex consumers

• Global and perpetual

• Effects on processes

– Carbon sequestration, invasive species, biogeochemical exchanges, etc.

• Removal-trophic downgrading

Trophic cascade

http://pubs.usgs.gov/fs/2010/3099/

http://www.ucc.ie/staff/memmers/Lough%20Hyne.htm

Alternative stable states

• Sets of unique biotic and abiotic conditions

• Basins of attraction – Set of individual conditions lead to long-time behavior

– Collection of all possible initial conditions of a dynamical state

• ASS- perturbations push ecosystem from one basin to another

Alternative stable states

• Tipping points

– Phase shifts – abrupt changes in ecosystem structure and function.

• Hysteresis

– Multiple states persist under equal environmental conditions

– Example: Tropical cloud forests

Connectivity

• Ecosystems are built around interaction webs

• Every species can potentially influence many others

• Interactions – Biological processes

– Physicochemical processes

– Highly complex network

Ecological Society of America http://phys.org/news/2012-10-scientists-greenbelts-wildlife-sanctuaries.html

Trophic Downgrading

• Not widely appreciated, difficult to observe

• Need for perturbation, to be perceived

• Time scales – When noticed, too late

• Space scales

• Sea Otter (nutria) – Population collapse – -herbivorous sea urchins – +kelp abundance

• Seastar – Prevents dominance mussels

(mejillon)

• Bass (robalo) – Reduce phytoplankton – Eats zooplanktivorous

• Large reef fish – Fisheries (left)

• Bass – Eats minnows – Promotes benthic algae

• Artic fox (zorro) – Eat seabirds – Reduces nutrients inputs

from sea to land

• Jaguar – Herbivore guild – Reduction plant

recruitment and survival

• Wolf – Elk (alce) browsing

• Wildebeest (gorgon) – Rinderpest (virus) – Increase biomass-fire

• Kelp increase enhances abundance of kelp forest fish

• Increases organic carbon- +growth rate of mussels

• Gulls (gaviotas) – Fish-

invertebrates

• Fish, mammals, birds

Discussion

• Management solution: restoration of apex consumers.

• Ecological surprises

– Pandemics, loss valuable sp., shifts ecosystem states, loss ES

– Altered top-down regimes

– Apex loss or introduction of exotics

Discussion

• What about other anthropogenic threats?

• Do present conservation strategies contemplate this new paradigm?

Surrogate species?

Species used to represent other species or aspects of the environment to obtain a

conservation objective. (Caro, 2010)

Indicator

Umbrella

Keystone

Flagship

Thanks for your attention!