6. Impacts of global change in aquatic ecosystems Flashcards
Overview of the lecture
- Physical effects of climate change
- The 2 main biological responses to changes in aquatic ecosystems
- Is size also going to be a biological response?
What are the 6 key physical effects of climate change on aquatic ecosystems?
1.1
- Increasing global temperatures (best case 1.9, worst case 8.5 by 2050, IPCC 2021)
- Arctic Sea Ice Loss (12% decline per year)
- Sea level rise (best case 0.5, worst case 1.75)
- Ocean acidification (may lead to shells and skeletons dissolving, Kroecker et al., 2013)
- Extreme weather events
- Increasing water temperatures (Lakes increasing by 0.34 per decade, on average. Leading to lakes drying, whilst some are rising. Contributing to changes in stratification).
What are the two main biological responses to changes in aquatic ecosystems?
2
- Phenology
- Range
Define phenology
2.1
The ‘timing of events in species’
Give an example of how the phenology of aquatic ecosystems is currently changing as a result of climate change
Edwards and Richardson, 2004 observed earlier dinoflagellate blooms from 1958 to 2002, triggering changes up the food web
Tao et al., 2018 found that fish reproduction in the Tibetan Plateau is getting earlier by 2.9 days per decade between 1970s to 2000s. This was found in the Otolith ear bones of fish to estimate reproduction
McCauley et al., 2018 found that the emergence of the Western Pondhawk is showing reduced larval survival with increasing temperatures, and extended seasons of emergence
Give an example of how the range of aquatic organisms is changing as a response to climate change?
2.3
Verges et al., 2018 observed the expansion of coral reefs into regions that they may not have previously been able to inhabit. This triggered changes in grazers etc., and the impacts were felt up the food web
Pinksy et al., 2020 found that the range of the Humboldt squid is increasing Northwards and Southwards, but their prey, the American Lobster, is only increasing northwards
What is the temperature-size rule?
3.1
Atkinson, 1994
Even at resting, organisms need more energy to stay alive at warmer temperatures.
A reduction in body size would mean that organisms would need fewer resources to keep up with rising metabolic demands
Smaller endotherms cope better than larger endotherms in a warmer world, due to their SA:V ratio
What is James’ rule?
3.2
James’ rule predicts a decrease in body size when populations experience warmer temperatures (James, 1970).
There will be larger individuals at higher latitudes, and smaller individuals at lower latitudes
This is by the same mechanism that the temperature-size rule functions by
What is Bergmann’s Rule?
3.3
The body size variation within a taxonomic group
Compares body size across closely related species of endotherms, and predicts that warmer localities tend to be inhabited by small-sized species
This is assumed to be a product of trade-offs between temperature and thermoregulatory advantages associated with SA:V ratios
LESS BROADLY ACCEPTED THAN TEMPERATURE-SIZE RULE
What is Kleiber’s Law?
3.4
States that bigger animals need more energy to survive, but will use their energy more efficiency.
Heat is a byproduct of metabolism, and the more efficient the metabolism, the less heat produced.
By reducing their body size, the organisms need fewer resources, and cannot keep up with rising metabolic demands
Are we seeing evidence of the temperature-size/Bergmann’s rule?
3.5
O’Gorman et al., 2017
There is some evidence of these rules coming into play in Greenland
We are seeing that warming favours the small, but only when temperatures are limited
However, the exceptions to this rule are seen if nutrient supply increases with temperature, then it can offset the higher metabolic demands of large consumers, allowing them to maintain their size
We can measure this in the Arctic using mesocosms/natural laboratories, which provide excellent, natural points of comparison.
What is the generally accepted hypothesis about what’s going on with size and climate change?
3.6
Warming does tend to favour the small across most taxonomic groups, but this is not universal
When resources are plentiful, there is no biological need to reduce body size
Proffitt et al., 2007 showed that patterns of shrinkage are less common in areas where increased precipitation and temperature may lead to a net increase in Primary Productivity. Therefore, in some instances, warming could favour the large
How is changes in size of organisms affecting diversity?
3.7
Jackson et al., 2024
Biodiversity is declining with some warming, but less so in environments with higher productivity - impacts unstable in higher latitudes
Regional impacts of warming on biodiversity are more stable in environments with low initial biodiversity - impacts stable in higher latitudes
