Key Concepts in Ecology: From Experiments to Niche Conservatism
Diamond (1983) – Types of Experiments
Identifies three types of experiments: natural experiments, lab experiments, and field experiments.
Each has unique strengths and weaknesses: lab experiments are good for isolating variables but are only feasible on small, fast-growing organisms and cannot capture the complexity of natural systems. Natural experiments are excellent for capturing complexity and large-scale (either time or space) processes, as well as things that are not ethical to actively manipulate, but variable isolation is impossible, and you have limited access since you’re reliant on things out of your control to create them. Field experiments lie somewhere in between, with some of the strengths and weaknesses of both.
All three types of experiments are necessary for ecology and complement each other.
Hutchinson (1961) – Paradox of the Plankton
Niche theory predicts two sufficiently similar organisms cannot indefinitely coexist without either natural selection driving them apart (niche partitioning) or driving one extinct (competitive exclusion).
Observation of ecology shows many organisms with very similar phenotypes all competing for the same limited resources – what maintains this diversity?
Several Possible Explanations:
Environmental variability means insufficient time for competitive exclusion to apply in many cases.
High levels of environmental heterogeneity mean that organisms aren’t actually ‘overlapping’.
Overlap may be the result of source-sink dynamics.
Ecological principles can be axiomatically true without being particularly useful in understanding what is going on.
Grime (1974) – Characterizing Plants
Given a limited allocation of resources, plants invest in some traits at the cost of others.
Generally speaking, plants can be good at living in stressful areas, highly disturbed (ruderal) areas, or highly competitive areas.
Being better at one trait comes at the cost of being good at other traits.
Habitats that are extreme in one way will have few species.
Moderate habitats have the most species.
Rosen (2021) – Humanity Is Flushing Away One of Life’s Essential Elements
Phosphorus is historically a major limiting nutrient for plants.
Humans have radically increased the rate at which phosphorus enters the environment.
Increased phosphorus does all sorts of detrimental things to ecology.
Mined phosphorus is pretty essential for feeding people.
We can’t rely on mined phosphorus forever.
Peñuelas et al. (2022) – The Bioelements, Elementome, and Biogeochemical Niche
Organisms require environmental inputs of many different elements (bioelements).
Each organism has its own specific elemental requirements (the elementome).
Every organism has strategies for acquiring the elements it needs, and these needs/strategies can be used to make ecological predictions (biogeochemical niche).
Taxonomic relationships, traits, and competition for nutrients can be used to predict an organism’s biogeochemical niche.
Stoichiometric needs of organisms are somewhat flexible, depending on environmental factors.
He et al. (2013) – Species Interactions and Stress
As stress increases, organisms increasingly rely on facilitative interactions or reduce competitive interactions.
Only studied in plants, but it had pretty universal support.
Species traits/evolutionary history did seem to affect the strengths of interactions.
Janzen & Martin (1982) – The Fruit the Gomphotheres Ate
Many North American trees have large, heavy fruit that do not spread from underneath the parent tree.
Looking at the ecology of these plants in their current settings, it’s basically impossible to explain why they’re like this.
Looking at their evolutionary past, they may have been dispersed by large land mammals that are now extinct, and now these trees are stuck (megafaunal dispersal syndrome, evolutionary anachronism).
Historical contingency and evolutionary constraints mean that an organism’s ecology can only be understood when taking into account its evolutionary history in addition to its present.
Wiens et al. (2010) – Niche Conservatism as an Emerging Principle
Emphasis is placed on natural selection causing change over time, but much of a species’ niche is determined by traits retained over its evolutionary history.
Many ecological processes will conserve traits over time, not select for new traits (stabilizing selection).
The principle of niche conservatism can be used to detect potential new areas of study and ask ecological questions.
Use assumptions that traits are conserved, then look at when they are not – this means strong selective pressures have occurred. The more different you are from your closest relatives, the stronger the pressures must be.