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)