Lecture 10: Tropic relationships in communities
Primary produced (autotroph): self-feeding , plants
Primary consumer: consumers of primary producers; herbivores from ants to zebras
Secondary consumers: carnivores who eats herbivores
Tertiary consumers: carnivores who eat secondary consumers
Detritivores: eat dead organic matters
Food webs (Functional web)
Emphasizes the influence of populations on growth rates in other populations.
Can only be revealed by experiments
Control experiment Insecticide treatment
Beetles abundant Beetles suppressed
High plant diversity Low plant diversity
Beetle here are Keystone consumers because when
they are removed, the edifice of the community tumbles
Interaction strengths are assessed by removal experiments.
Hairston, Smith & Slobodkin
Suggested that the earth is green because carnivores depress the populations of
herbivores that would otherwise consume most of the vegetation.
Indirect effect: one trophic level exerts influences on a send by affecting a third.
o Cascades involves effect that alternate across trophic levels.
when higher trophic levels
determine the sizes of the
trophic levels below them.
when the size of a trophic
level is determined by the
rate of production of its food
Experiment by Knight et al.
(2005) The presence of fish in a pond
reduced the abundance of dragonfly larvae,
which reduced the abundance of dragonfly adults,
and thereby increased the abundance of
pollinators and the number of seed produces by
Adding fish to a pond improves the
reproductive success of a plant on land.
Difficulty of herbivory
Plant tissues are hard to convert into animal tissues
o Cellulose and lignin tough, indigestible without microbial symbionts
o Plant tissues heavily defended against herbivores, mechanically and
o Coevolutionary race between plants and insect herbivores is responsible for
much of biodiversity; specialization is common.
Milkweeds vs. Monarch butterfly larva
Milkweeds contains repellent latex under pressure in leaf veins (poisonous)