Other Interspecific Interactions

1
Other Interspecific Interactions

• Chapter 7

2
Interspecific Interactions

• Symbiosis - intimate association between
  individuals of different species, in which one
  lives on or in the other

3
Interspecific Interactions

• Commensals - guests - neither harmful nor
  beneficial to the host
• Use surface of the host as a place to live

4
Interspecific Interactions
Epiphytes - bromeliads, Spanish moss
5
Interspecific Interactions
6
Interspecific Interactions

• Mutualism - relationship of benefit to both
  organisms
• Enhanced growth, survival, reproduction in
  presence of each other (mirror-image of
  competition?)

7
Interspecific Interactions

• Obligate for each (required)
• Facultative for each (helpful, but not required)
• Mixture

8
Culture of crops/livestock

• Humans and domesticated plants/animals
• Ants and fungus

9
Pollination

• Insects, birds, bats as pollinators
• Reproduction for plant, food reward for pollinator

10
Gut Inhabitants

• Cattle rumen with bacteria
• Termite gut with protozoans, bacteria

11
Mycorrhizae

• Fungus and root tissue
• Fungus increases water, nutrient uptake
• Plant root supplies organic carbon

12
Algae Animals

• Hydra with Chlorella
• Coral with dinoflagellates (side effect of
  photosynthesis is precipitation of calcium
  carbonate)

13
Lichens

• Fungus and algae
• Fungus absorbs water, nutrients
• Algae photosynthesizes, provides organic carbon
  (algae often in obligate relationship)

14
Interspecific Interactions

• Parasitism - obtains nutrients from one or few
  hosts
• Normally causes harm, but not death
• Often includes pathogens (disease-causing),
  viruses
• Superabundant - gt half of species on earth

15
Microparasites

• Bacteria, viruses, protozoa, fungi
• Multiply directly within host (usually within
  cells)

16
Microparasites

• Transmitted directly from host to host (VD,
  influenza)
• Transmitted by vector (some other animal)
  (malaria, sleeping sickness)

17
Macroparasites

• Flatworms, roundworms, insects
• Grow in/on host, produce infective stage that
  leaves, live within body cavities or
  intercellularly

18
Macroparasites

• Transmitted directly (intestinal nematodes, lice,
  plant fungi)
• Transmitted indirectly (tapeworms, flukes)

19
Transmission

• Transmission rate depends on host density
• Rate increases with density (susceptible hosts
  only - genetics)

20
Distribution

• Distribution is clumped (site-specific)
• Few hosts have large numbers, most have none
• High intensity of infection, low prevalence

21
Response of hosts

• Die in whole or in part
• Biotrophic parasites require living hosts
• Necrotrophic parasites prefer dead hosts
  (pioneering decomposers)

22
Plant hosts

• Infected cells die immediately - hypersensitivity
• Surrounding cells produce phytoalexins to prevent
  spread of parasites

23
Invertebrate hosts

• Phagocytic cells engulf foreign particles

24
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

25
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)