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ZOL 3702 LEARNING UNIT 7THE NATURE OF PREDATION
Textbook reference: pg 266 - 278
Learning outcomes:
Describe and apply the different classifications of predators.
Describe and explain the effect of herbivores on individual plants.
Describe and explain the effect of predators on the prey population.
Describe and explain the effect of consumption on the consumer.
Consumers, in this case predators, influence the distribution and abundance of what they consume.
Predation is the consumption of prey by the predator, in which the prey is still alive when the predator
first attacks it.
THE CLASSIFICATION OF PREDATION: pg 266 – 267
Consumers affect distribution and abundance of things they consume, and these effects are important.
There are two possible ways to classify predators: neither is perfect, but both can be useful:
- Taxonomic classification, for example carnivores, herbivores, and omnivores.
- Functional classification , for example true predators, grazers, parasitoids, and parasites.
True predators kill their prey immediately after attacking and kill many pray throughout their lives. They
consume part of all the whole prey. True predators are mainly carnivores but can also be seed eaters.
Grazers also use many prey during the course of their lives, but they eat only a part of the prey. The attack
is seldom fatal. Examples include large herbivores and leeches.
Parasites consume parts of their prey, the host , and are typically harmful but rarely lethal in the short
term. They usually feed on one or more hosts. There is a narrow relationship between the parasite and the
host. There is an intimacy of Association between parasites and their hosts.
Parasitoids are insects that show specific behavior when they lay eggs, they lay their eggs in the host
which leads to the death of the host. The adults are free-living, but the larvae live in close association with
the host. Parasitoids play an important role in population dynamics. It is estimated they account for more
than 10% of world species. The rate of predation is determined by rate at which adult females lay eggs.
THE EFFECT OF HERBIVORES ON INDIVIDUAL PLANTS: pg 267 – 274
The effects of herbivores on a plant depend on which herbivores are involved, which plant parts are
affected, and the timing of the attack relative to the plant’s development.
Herbivores can be true predators, grazers, or parasitic consumers.
Browsing, sap sucking, meristem feeding, fruit and flower damage, and root eating have different effects
The consequences of defoliating a germinating seedling are unlikely to be the same as those of defoliating
a plant that is setting its own seed.
Because plants usually remain alive in short term, effects of herbivory are dependent on response of plant.
Plants may show tolerance of herbal damage or resistance to attack.
TOLERANCE AND PLANT COMPENSATION:
Plant compensation is a term that refers to the degree of tolerance exhibited by plants.
If damaged plants have greater fitness than their undamaged counterparts, they have overcompensated.
If they have lower fitness, they have under compensated for herbivory.
Individual plants can compensate for the effects of herbivory in a variety of ways.
The removal of shaded leaves may improve balance between photosynthesis and respiration in the plant.
In the immediate aftermath of an attack from a herbivore, many plants compensate by utilizing reserves
stored in tissues and organs or by altering the distribution of photosynthate within the plant.
Herbivore damage may lead to an increase in the rate of photosynthesis per unit area of surviving leaf.
Often there is compensatory regrowth of defoliated plants when buds that would otherwise remain
dormant or stimulated to develop.
There is also a reduced death rate of surviving plant parts.
Herbivory mobilizes stored carbohydrates and increases root growth.
The plant can also compensate for the loss of pods with larger seeds.
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