Other Interspecific Interactions Chapter 7
Dec 29, 2015
Other Interspecific Interactions
Chapter 7
Interspecific Interactions Symbiosis -
intimate association between individuals of different species, in which one lives on or in the other
Interspecific Interactions Commensals -
“guests” - neither harmful nor beneficial to the host
Use surface of the host as a place to live
Interspecific Interactions
Epiphytes - bromeliads,Spanish moss
Interspecific Interactions
Interspecific Interactions Mutualism -
relationship of benefit to both organisms
Enhanced growth, survival, reproduction in presence of each other (mirror-image of competition?)
Interspecific Interactions Obligate for each
(required) Facultative for each
(helpful, but not required)
Mixture
Culture of crops/livestock
Humans and domesticated plants/animals Ants and fungus
Pollination
Insects, birds, bats as pollinators Reproduction for plant, food reward for pollinator
Gut Inhabitants
Cattle rumen with bacteria Termite gut with protozoans, bacteria
Mycorrhizae
Fungus and root tissue Fungus increases water, nutrient uptake Plant root supplies organic carbon
Algae & Animals
Hydra with Chlorella Coral with dinoflagellates (side effect of
photosynthesis is precipitation of calcium carbonate)
Lichens
Fungus and algae Fungus absorbs water, nutrients Algae photosynthesizes, provides organic carbon
(algae often in obligate relationship)
Interspecific Interactions Parasitism - obtains
nutrients from one or few hosts
Normally causes harm, but not death
Often includes pathogens (disease-causing), viruses
Superabundant - > half of species on earth
Microparasites
Bacteria, viruses, protozoa, fungi Multiply directly within host (usually within
cells)
Microparasites
Transmitted directly from host to host (VD, influenza)
Transmitted by vector (some other animal) (malaria, sleeping sickness)
Macroparasites
Flatworms, roundworms, insects Grow in/on host, produce infective stage that
leaves, live within body cavities or intercellularly
Macroparasites
Transmitted directly (intestinal nematodes, lice, plant fungi)
Transmitted indirectly (tapeworms, flukes)
Transmission
Transmission rate depends on host density Rate increases with density (susceptible hosts
only - genetics)
Distribution
Distribution is clumped (site-specific) Few hosts have large numbers, most have none High intensity of infection, low prevalence
Response of hosts
Die in whole or in part Biotrophic parasites require living hosts Necrotrophic parasites prefer dead hosts
(pioneering decomposers)
Plant hosts
Infected cells die immediately - hypersensitivity Surrounding cells produce phytoalexins to
prevent spread of parasites
Invertebrate hosts
Phagocytic cells engulf foreign particles
Vertebrate hosts
Immune responses - several types of killer cells with “memory”
Inhibits future infection by same things Response most effective for bacteria, viruses Response least strong for macroparasites, protozoans
Bottom Line
Reduced survival, growth, fecundity, competitive ability of host
Some evidence that parasites may be chief factors controlling populations of some organisms (e.g., humans)