Eco Lec - Chapter 6 Species Interactions

• Mutualism


  Species interaction benefiting two organisms
• Competition


  Harm both organisms
• Predation, herbivory, parasitism


  Benefit one but harm the other
• Commensalism


  Benefit one but not harm the other
• Competition


  • Exists when a particular resource is in limited supply
• Intraspecific competition


  Occurs between individuals belonging to the same species
• Intraspecific competition in plants


  • Nutrients, water, or sunlight
  • Invest more in the formation of roots than shoots
• Self-thinning


  Some plants die because of competition for soil nutrients and water, remaining plants will then show faster growth because of more nutrients available, thus, have greater biomass
• Ways to Reduce Intraspecific Competition

  1. Young members of an animal population may disperse to less crowded areas

  2. Plants are dispersed when wind, water or animals carry their seeds

  3. Animals with strong territorial instincts that keep out their offspring or trespassing adults from their vicinity which minimizes competition

  4. Resource partitioning or niche differentiation
• Interspecific competition


  Occurs when the individuals came from different species and both can occur at the same time
• Organism's Niche


  Describes the physical and chemical requirements of an organism, the effects of other organisms on its survival, growth and reproduction and its effects on other organisms
• Niche


  Role (profession) of the species in its community, ecological role of a species, i.e., a species relation to its abiotic and biotic environment, all the physical (temp, light, etc), chemical (pH, salinity, nutrients, etc.) requirements of an organism and the effects of other organisms on its survival and reproduction
• Competitive Exclusion Principle


  No species having identical niches or requirements can co-exist indefinitely
• Competitive Exclusion Principle


  • P. Caudatum & P. aurelia - in different test tubes with constant amount of food, two populations reached their carrying capacity, in the same test tube, P. aurelia survived while P. caudatum was eliminated due to competition for food, since the two species had the same niche
• Fundamental niche


  Multidimensional space (in terms of temp, pH, salinity, sunlight, etc.) which an organism can occupy in the absence of competitors, predators, etc.
• Realized niche


  Smaller multidimensional space actually occupied by the organism because of the presence of certain biotic constraints, like predators
• Realized niche


  • The fundamental niche of G. saxatile and G. sylvestre included both acidic and basic soils. However, due to competition with G. sylvestre, the realized niche of G. saxatile was narrowed down to acidic soil; on the other hand, the realized niche of G. sylvestre was narrowed down to basic soil
• Resource partitioning or niche differentiation


  Competition results in co-existence of two species, two or more species competing can co-exist if they use resources in slightly different ways or have slightly different requirements, this is still reversible
• Character displacement


  Process of evolution which results in divergence of traits in competing species
• Competition helps shape a community by affecting the local distribution of species. The niche concept does not only give the idea of what environmental factors a particular organism tolerates or the resources it uses, it also helps us understand why a community is organized in a certain way
• Introduction of an exotic or introduced species in an area where it is not naturally found also show the importance of competition in structuring communities as it outcompetes the native species that can lead to its extinction
• Introduced species


  • Golden apple snail (golden kuhol) Pomacea canaliculata
• Mutualism


  Interaction between two species where the fitness of the two species is increased
• Obligatory mutualism


  Two species cannot survive without the other
• Facultative mutualism


  Two species can live separately with each other
• Common Mutualistic Relationships


  • Alga and fungus making up a lichen, with the alga providing organic compounds to the fungus and the fungus providing moisture to the alga
  • Protozoa that live in the intestines of termites and have enzymes for the digestion of cellulose while the termite provide protozoa with food
  • Plants and their pollinators
  • Plants and the ants that protect the plants from predators while the ants obtain food from the plants
  • Leguminous plants and nitrogen-fixing bacteria (Rhizobium sp.) in the root nodules
  • The roots of 90% of all plants and fungi in the relationship called mycorrhizae
  • Corals and unicellular. photosynthetic algae called zooxanthellae
• Mycorrhizae


  Fungi form a netlife structure around root cells that increase the surface area for absorption of nutrients (Cu & Zn) which are held by the negatively-charged soil particles, as well as, P, N, and H2O. In exchange, fungi obtain organic substances exuding from the roots and plants
• Zooxanthellae


  Coral polyps obtain carbohydrates from them while the corals provide nutrients, esp N and P
• Exploitation


  Includes predation or herbivory, parasitism and pathogenicity, species interactions where one species benefits while the other is harmed
• Herbivores


  Consume live plant material but do not usually kill plants
• Predators


  Kill and consume other organisms, usually other animals
• Parasites


  Live on the tissues of their host, often reducing the fitness of the host but generally not killing them
• Pathogens


  Cause disease in their hosts
• Camouflage


  Some species have the same color as their background
• Aposematism


  Species that are venomous (frogs, sea snakes, etc.) have distinct patterns or bright coloration to warn enemies
• Batesian mimicry


  Certain harmless species resemble poisonous or unpalatable ones to gain protection from predators when the latter remember a bad experience with the actually toxic organism
• Mullerian mimicry


  Different species, both or all of which are harmful or poisonous, resemble one another
• Predators, parasites, and pathogens influence the population distribution and abundance of host or prey populations
• Predators, parasites, and pathogens


  • Prickly pear cactus, Opuntia stricta - exponential increase in their population size, one of the problems encountered when species are introduced into areas where they are not a native to
• Refuges


  Situations in which members of an exploited population have some protection from predators and parasites, not necessarily a place where a prey or host can hide from its exploiter