6. Species Interactions

• • Ecological Community 
  • assemblage of populations of at least two different species
  • Interact directly or indirectly in the area
• • Each kind of organism is equipped with the necessary structural, physiological and behavioral characteristics to obtain and digest their food. 
  • Processes: food web, nutrient cycling
• • benefit the two organisms
  • mutualism
  • symbiosis
• • harm the two organisms
  • competition
• • benefit one but harm the other
  • predation
  • herbivory
  • parasitism
• • benefit one but not harm or benefit  the other
  • commensalism
• Competition

  • exists only when a particular resource is in limited supply.
• • Intraspecific competition 
  • Competition with members of own species 
  • occurs between individuals belonging to the same species
  • members of the same species must compete with each other because they occupy the same ecosystem and have the same niche
  • Interspecific competition 
  • Competition between individuals of two species (reduces fitness of both)
  • occurs when the individuals come from different species and both can occur at the same time
• • Niche 
  • Ecological role 
  • 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
• • Intraspecific competition 
  • gorillas fighting for a mate, plants competing for sunlight, nutrients, or water
• • Among plants, intraspecific competition may be for nutrients, water or sunlight.
  • below ground competition
  • sometimes more intense than the competition for sunlight.
• • Self-thinning rule in herbaceous plants (Molles, 2006)
  • It predicts that plants will decrease in population density as the total biomass of the population increases
  • Plants grow in biomass as population density decreases
• • When there is competition for water or nutrients, plants tend to invest more in the formation of roots than shoots.
• 3 WAYS TO REDUCE INTRASPECIFIC COMPETITION

  1. The young members of an animal population may disperse to less crowded areas.
  2. The second way is shown by animals with strong territorial instincts that keep out their offspring or trespassing adults from their vicinity which minimizes competition.
  3. Lastly, competition is reduced through resource partitioning or niche differentiation which happens not only in intraspecific competition but also in interspecific competition
• • Interspecific competition
  • chickens fighting over food or fish over territory in a coral reef. 
• Adress - a place where an organism lives; its habitat
• Niche - role or profession of species in its community
• Niche

  • the ecological role of a species (Miller and Spoolman)
• Niche

  • all the physical (temperature, light), and chemical (salinity, nutrients) requirements of an organism and the effects of other organisms on its survival and reproduction
• Importance of Niche Concept (Gause) 1937

  • Competitive Exclusion Principle - no two species having an identical niches or requirements can co-exist indefinitely
  • Paramecium caudatum and Paramecium aurelia
  • When he grew them in the same test tube, P. aurelia survived and P. caudatum was eliminated
• Hutchinson (1957) distinguished between fundamental and realized niche
• Fundamental niche - multidimensional space (in terms of temperature, ph, salinity, sunlight) which an organism can occupy in the absence of competitors, predators, etc.

  Realized niche - refers to smaller multidimensional space actually occupied by the organism because of the presence of certain biotic constraints like predators, etc.
• Existence of fundamental and realized niche (Tansley, 1917)

  • Gallium saxatile and Gallium sylvestre
  • G. saxatile grew in acidic soil; G. sylvestre grew in basic limestone soil
  • The two species were able to grow in both acidic and basic soil (fundamental niche)
  • When both are in acidic soil, G. saxatile prevailed in acidic (realized niche)
  • When both are in basic soil, G. sylvestre prevailed in basic (realized niche)
• Competition results in co-existence of two species if resource partitioning or niche differentiation occurs
• Existence of fundamental and realized niche

  • Chthalamus sp. and Balanus sp.
  • Fundamental niche of Chthalamus sp: upper to lower intertidal zones; Realized niche: upper intertidal zone
  • Fundamental and realized niche of Chthalamus sp: middle to lower intertidal zone
• Campbell (1996)

  • The niche differentiation is the ghost of competition past
• Character displacement

  • To reduce the effect of competition (reduce the fitness of competing species), natural selection favors the decrease in the niche overlap, thus reducing competition.
  • The process of evolution which results in divergence of traits in competing species
• Cases of Character Displacement

  • Galapagos finches
  • Sympatric speciation - Medium-sized finch lives together with small-seized finch.
  • The size of beaks are very different
  • Allopatric speciation - Finches are found in different islands
  • The size of beaks are similar
  • Evolution has reduced the niche overlap; resulting in different niches of finches, niche divergence
  • Evolutionary response to competition is the change in fundamental niches
• Factors that influences the survival and reproduction of finches

  • Galapagos finches - the kinds of seeds eaten by different species
  • Balanus - physical factors like sunlight and dehydrating effect of wind
• Competititon between an introduced and an indigenous species

  • Batillaria attrimentaria and Certhidae californica
  • When a species if brought to another place where it is not found naturally, its population density often increases.
  • Introduced: B. attrimentaria brought to US with intentially introduced Japan oysters
  • Indigenous: C. californica
  • The abundance of C. californica is now lower while B. attrimentaria has increased
  • Species competed for the same resource
• The exotic or introduced species outcompetes the native species that can lead to the extinction of species

  • golden apple snail, Pomacea canaliculata, introduced to the Philippines from Taiwan is now a major pest of rice
  • zebra mussels in the Mississippi River which came from the Caspian Sea in Europe and competes with the native fishes for plankton and shellfishes for space
  • Giant ants introduced in the US resulted in the death of 16 native ant species
• • Obligatory mutualism - the two species cannot survive without the other
  • Facultative mutualism - the two species can live independently with each other
• Mutualistic relationships

  • (a) the alga and fungus make up a lichen, 
  • the alga providing organic compounds to the fungus 
  • the fungus providing moisture to the alga (obligatory mutualism).
  • (b) protozoa that live in the intestines of termites and have enzymes for the digestion of cellulose while the termite provides the protozoa with food.
  • (c) plants and their pollinators 
  • Pollinators will disperse the pollens of plants
  • Pollinators may also lay their eggs on the plant
  • (d) plants and the ants
  • the ants that protect the plants from predators 
  • the ants obtain food from the plants
• Mutualistic relationships

  • (e) leguminous plants and nitrogen-fixing bacteria (e.g., Rhizobium sp.) in the root nodules
  • Bacteria fixing the nitrogen so that the plant can use and absorb the fixed nitrogen
  • Bacteria will receive nutrition from the plant in the form of organic acids
  • (f) the roots of 90% of all plants and fungi in; the relationship called mycorrhizae
  • (g) corals and unicellular, photosynthetic algae called zooxanthellae.
• Myccorhizae

  • fungi form a netlike structure around root cells that increase the surface area for absorption of nutrients
• Corals and zooxanthellae

  • Coral polyps obtain carbohydrates from the zooxanthellae
  • Corals provide the zooxanthellae with nutrients, especially nitrogen and phosporus
• • Herbivores - consume 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
• Plant and animal adaptations to avoid predation

  • Physical and behavioral defenses - having thorns and fighting with claws, hiding, or running away
  • Chemical defenses - releasing noxious substances or toxins or the presence of unpalatable substances in leaves
• • Camouflage - species having similar pattern or color as their background
  • Aposematism - certain species that are venomous have distinct patterns or bright coloration to warn away 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 actual toxic organism
  • Mullerian mimicry - different species, both or all which are harmful or poisonous, resemble one another to work as an added advantage because potential predators do not try to eat species that they have not tasted yet because of a previous bad experience; monarch and viceroy butterfly