Struggle for Existence pt. 9 Flashcards
Autotrophs
also called primary producers, collectively constitute the first trophic level of a community, make their own energy
Heterotrophs
consumers
second trophic level
herbivorous animals that eat plants (secondary producers or primary consumers)
Carnivores
prey on live herbivores, called tertiary producers or secondary consumers
Omnivores
consume from more than one trophic level
Detritivores
decomposers, extract their carbon from dead organisms
The earth is mostly a….
closed system.
Where can elements on earth be found?
Oxygen, nitrogen, and carbon are highly mobile elements that are closely tied up with the metabolisms of organisms. Phosphorus and others are trapped in stable insoluble abiotic forms (sedimentary rocks at bottom of ocean)
HSS
Green earth hypothesis - because the earth is still green, the third trophic level must inhibit the second so that the first doesn’t get wiped out
Counterpoints to Green earth hypothesis
- maybe not all leaves are edible
- only applies to whole trophic levels (does not allow for nuances within trophic levels)
- its actually pretty difficult to identify which trophic level an organism resides on
How can we quantify organismal trophic level?
measuring ratios of stable isotopes in its tissues (carnivores almost always turn out to be omnivores)
trophic cascades
measurable, important, indirect relationships between two trophic levels that are mediated through a third level (level three indirectly causes increase in level one by depressing level two)
Tiffany Knight
dragonfly experiment
Why are isolated communities used to test trophic cascades? What are some issues with this?
Small isolated communities allow for removal experiments (top down; actually getting all the secondary consumers out) or bottom up (removing primary producers). Some problems
- negates metapopulation structure and interpatch migration
Microcosms and mesocosms
experiment environments (small vs large scale ish)
Where are trophic cascades more likely?
Aquatic environments because the habitat is not separated into discrete patches (one homogenous solution with few dispersal barriers). Behave as populations not metapopulations.
Folivory
leaf eating
Structural defences
thorns, spiky hairs, abrasive silica, physical toughness of sclerophyllous leaves
chemical defences
metabolic poisons or deterrents
Secondary compounds/metabolites
chemicals not involved in primary processes of a plant (photosynthesis, respiration, etc) rather act as a defence against herbivores
Why do some plants lack protective chemicals? What happens to these plants?
Artificial breeding for palatable crops or knockout genes. Makes them highly susceptible to attack
Which came first: herbivory or diversification?
Herbivory. Evolutionary arms race between plants and herbivorous insects can lead to local specialization and thus eventually speciation.
Developing resistance often leads to
specialization- sometimes the harmful compound even becomes a chemical cue to find the plant, feeding stimulant, a cue for egg-laying, or is incorporated into the insect’s tissue (monarchs)
Erlich and Raven
Studied herbivory and diversification. Looked at parallel adaptive radiations.
Which is more specialized: interactions that are hostile or not?
Hostile interactions lead to specialization and thus speciation more so than (insects eating or harming plants) milder interactions which are typically more generalized (pollinators and flowering plants).
Which lineages have produced more species: carnivorous or herbivorous?
Herbivorous. We can see branching points in the phylogeny of insects where one became herbivorous and one remained carnivorous. Herb. lineages produced more species in same amount of time.
Why doesn’t specialization occur in large bodied herbivores?
They can move around in their habitat and make choices as to what it eats (mixed diet/generalists which avoids worst poisons) thus they do not have highly specific detox pathways. Many insects are born and die on same plant thus they must be able to handle plant defences or they will die!!
