13. Ecosystem structure and function Flashcards
Structure of the lecture
- Drivers of biodiversity loss
- Synergisms in drivers
- Species-level consequences
- Community-level consequences
- Ecosystem-level consequences
- Future consequences
What are the 5 main drivers of biodiversity loss?
1.1
- Habitat change
- Climate change
- Invasive species
- Over-exploitation
- Pollution
What can we use to model the major drivers of anthropogenic change?
1.2
Planetary Boundaries Framework
Millenium Ecosystem Assessment
What are the 3 major methods by which habitat change is damaging nature?
1.3
- Habitat LOSS, which causes altered species abundances and extinction due to decreasing species area and smaller populations
- Habitat FRAGMENTATION, which involves the splitting of habitats into smaller and smaller and more islated patches, which leads to edge effects and subdivision
- Habitat DEGRADATION, which involves the declining quality of existing habitats, and invokes both loss and fragmentation. Directly impacts both food web and structural habits
How can synergistic effects influence drivers of biodiversity loss?
2.1
Drivers of biodiversity loss can be:
- Fully additive (all drivers add up to the sum of their constituent parts)
- Partially additive (all drivers add up to less than the sum of their constituent parts)
- Synergistic (all drivers add up to more than the sum of their constituent parts
How can synergisms impact conservation success?
2.2
Conservation that limits only the primary effects of biodiversity loss negates the fact that drivers can be intrinsically connected, and means that synergisms are hard to limit
What are the 4 species-level responses to climate change?
3.1
- Adaptationin situ
- Shifting distribution
- Shifting phenologies
- Extinction
Example of species responses to global change?
3.1
Speckled Wood butterfly
Undergoing shifting distributions, which has been seen through expansion northwards from 1970-1997
Undergoing shifting phenology, following changing budbursts of trees, emergence of insects, or the migration and breeding of vertebrate predators
How do species generalists and specialists respond differently to global change?
3.3
Generalist species can change their range more easily, and keep pace with the changing food sources/environment associated with climate change
Specialist species cannot change their range as easily, and will experience a more fragmented world than generalists
What are the major community-level consequences that are seen as a result of climate change?
4.1
- Food-web disruption leading to trophic cascades
- Biotic homogeneisation
- Decreasing robustiness/resilience
- Decreasing stability
- Idiosyncratic change
How can food web disruption lead to trophic cascades?
4.1
Keystone predators tend to increase as habitat are degraded, leading to top-down negative effects.
Prey species are expected to decrease, meaning we would see bottom-up negative effects.
Apparent competition may then arise from predators.
Trophic cascades lead to immensely complex propagation of impacts.
How can global change lead to biotic homogeneisation at the community level?
4.2
Attributed to monoculture, and leading to the decline in ecosystem functioning
How can changes to specific interactions be hard to predict?
4.3
Interactions between species are environmentally dependent, so hard to predict.
How can responses to climate change be idiosyncratic?
4.5
Showed that different conversion and degradation of habitats had different results on different taxa.
Secondary and plantation forests are more likely to have lower species accumulation than for primary rainforests.
Different species react in different ways.
How can interconnected species act as conduits of change?
4.4
Post et al., 1999
For example, in years with strongly negative NAO index, heavy snowfall led to wolves hunting in larger packs, meaning that the number of moose killed per day increased. Moose abundance decreased, and growth/understory increased.
How can changes to ecologcal communities impact ecological services?
5.1
Loss of ecological services
Due to land-use change, biotic introductions, changes to soil, changes to natural cycles, and and changing species composition/diversity
This results in changing biotic functional traits , ecosystem processes and thus, regional processes
IPBES, 2019, showed that 14/18 of the traditional ecosystem services are declining
What is the relationship between biodiversity and ecosystem functioning?
5.2
There is an overwhelmingly positive relationship between biodiversity and ecosystem functioning. This applies in different ecosystems, and different trophic groups. Klein et al., 2003, showed that pollination services increase with the richness of wild bees and proximity to their natural habitats
What is the relationship between functional traits and ecosystem services?
5.3
Functional traits are important for ecosystem services.
Gagic et al., 2015 showed that species richness matters less than functional diversity.
Flynn et al., 2009, showed that climate change is reducing the functional diversity of species across a broad range of taxa.
How are species declines leading to lowered ecological services?
5.3
Multiple species are required for ecosystem functioning.
Diversity begets stability at the community level - more species means more stability
What is the Insurance Hypothesis?
5.4
Tilman, 1999
The Insurance Hypothesis. Even when high diversity is not critical, or under constraint, it might be important in changing conditions. Having high diversity provides an insurance against environmental change.
What is the importance of maintaining redundant species?
5.5
Isbell et al, 2011
Different species matter at different times and locations. Short term, small scale studies focused on a single function will underestimate the importance of having many species. Care is needed before concluding that species are functionally redundant.
What are the 3 main methods that we can use to model the structure and function of ecosystems?
6.1
- Manipulation experiments (gives a clear understanding of specific processes, but often on a small scale)
- Observations (these can be larger scale, with a large range of processes, but mechanisms can often be hard to infer)
- Systems modelling/theory building
