“Nature is not fragile... what is fragile are the ecosystems services on which humans depend”. (Levin 1999)
Ecosystem resilience Amount of disturbance a system can take without changing states o Ability to reorganize, renew after disturbance o capacity to self-organize o Learning and adaptation
Response diversity Definition Diversity of responses to environmental change among species that contribute to the same ecosystem function Diversity within functional groups is important to the adaptive capacity of ecosystems; not just species richness
Role of Biological Diversity in Ecosystem Resilience Functional diversity Ecologically redundant (eg. Both fungi and bacteria are decomposers) Species diversity eg. Many species of decomposer fungi (may have a range of decomposing ability...example: may differ in optimal temperature) Response diversity
Response Diversity Example: seed dispersal in tropical forests Western Polynesia after cyclone Frugivore species disperse tree seeds Frugivore flying foxes, the dominante P. tonaganus and D. pacifica declined by 90% whereas P. samoensis declined by only 10%. P. samoensis, previously subdominant, was able to maintain function (seed dispersal)
Response Diversity Example: plants in rangelands Rank abundance with fill depicting different function Dominant species are functionally different Grazed grass replaced with functional e quivalent (Walker et al. 1999)
Response Diversity Example: freshwater detritovores Stoneflies are sensitive to organic pollution Crustaceans are sensitive to acidification Both break down leaf litter Species richness did not affect leaf breakdown rate, but species identity did.
Response Diversity Example: coral reef grazers Coral reef is made of framework-builders, primary producers, herbivores, predators Herbivores eat algae which blooms in their absence. Algae eventually kills reef Sea urchins graze, but are not resilient to disease, get wiped out, algae takes over, dead reef Sea urchins are not functional
Response diversity across scales Palm seed dispersal across a range of scales – Small rodents 5m (maintains patch of palms) – Tapiers 2km (establishes new palm patches) With disturbance such as hurricane, some patches may be wiped out, but others will remain to re-populate
Response diversity across scales Example: coral reef
Response Diversity Other examples? Can we describe the pine beetle outbreak using this concept? Other examples? How do we manage ecosystems with response diversity in mind?
Response diversity across scales Coral reef reduced competition between species that feed at different scales (frequency and distance) All contribute to the same ecosystem function: eating the algae and preventing a bloom, which would precipitate coral bleaching and death
Managing response diversity Reduce human homogenization of landscapes Avoid elimination of functional groups (ex. predators) Consider response diversity to maintain ecosystem buffering capacity, in order to maintain the ecosystem services we rely on Testable
Managing response diversity More barley cultivars in Finland is not better because they all have similar drought tolerance.
Quantifying response diversity (Kahiluoto et al. 2014) construct diversity index (similarity index) and validate with real data. Determine how far are we from resilience
Response diversity in Forests What is the goal? Productivity? Resistance to pest outbreaks (pine beetle)? What are the critical factors? How do we estimate the impact? Can we model responses, validate models?