Chapter 14 – Ricklef’s
All non-photosynthetic organisms must eat, and all organisms are at risk of being eaten. Therefore, C-R interactions are the most fundamental interactions in nature
• i.e. Predator-prey, Herbivore-plant, parasite-host
Other Types of interactions
• Competition (both parties suffer)
• Mutualism (both parties benefit)
• Commensalism (one party benefits, the other unaffected) – e.g. crab using a dead snails shell
• Amensalism (one party suffers, the other unaffected) – e.g. an elephant steps on a grasshopper
Types of consumers
• Parasite – feeds on host but is not direct cause of death (some cause disease or affect fecundity)
• Parasitoid – lays its eggs in the tissues and kills its host once the eggs develop into pupa
• Herbivore – can function as parasite in grazing and browsing or predator in full consumption
• Detritivore – feed on dead matter so don’t directly affect populations of resources
The ability to perceive predation risk is widespread in the animal world and has a strong effect on the behavior and habitat selection, as well as on the demography, of prey organisms – these responses have been strongly selected over the evolutionary history of the c-r interaction.
Defense mechanisms of prey can affect population growth.
It is believed that many mutualistic relationships have evolved from host-parasite interactions and perhaps vice versa.
Virulence is the measure of the capacity of a parasite to invade host tissues and may be reduced by actions of the host’s immune system (e.g. inflammation responses and production of antibodies)
Cross-Resistance – when a host is able to resist a new parasite that is closely related to another parasite that a host has built antibodies for in the past.
Plants often develop mechanisms to discourage their consumption – low nutrition in their tissues or chemicals that make the plant taste bad to consumers. If the soil is poor, the plants may not have the energy to produce these defensive chemicals, which can have a direct and negative effect on that plants population.
Trophic Cascades indirect interactions that are felt across multiple trophic levels. E.g. when a predator consumes its prey, it reduces the prey population, which benefits the plant population that the prey feeds on.
Exploitation or Indirect competition is when two consumer populations that compete for the same resource may never come into contact with each other, but are nonetheless negatively affected by the competition for the resource.
Mutualisms fall into three categories: Trophic, defensive & dispersive
Trophic mutualisms are usually specialized in complementary ways to obtain energy and nutrients.
Defensive mutualisms receive food or shelter from the partners in return for defending those partners against their consumers
Acacia Example (the tree provides sugars in the base of leaves and fats and proteins in the nodules of the leaves for the ants and shelter in the thorn bases while the ant protects the tree from consumers – other insects and will swarm vertebrate herbivores that attempt to feed on their host plants) An adaptation of each – the ants are active day and night (unusual for ants) and therefore can protect the acacia all the time. The acacia maintains its leaves all year to provide a food source for the ants even though similar species of acacia do not. Both species are dependent upon one another for survival.
Dispersive mutualisms include those that transport pollen between flowers in return for rewards such as nectar or that eat nutritious fruits and disperse the seeds they contain to suitable habitats.