7. Community Ecology

• • Community 
  • made up of the populations of different species that live together in a particular place and interact with one another. 
• • community 
  • often used in a narrower sense to refer to a subset of the species, such as a plant, bird, or fish community, 
• • Cunningham and Cunningham (2007) 
  • communities have emergent properties which are as follows: 
  • (1) species diversity, 
  • (2) community structure,
  • (3) resilience, and 
  • (4) stability.
• • Smith and Smith (2009) 
  • also consider the nature of species interactions in the community as an emergent property of communities.
• • Species diversity 
  • Refers to the number of different species in a community combined with either species richness and/or species abundance 
• • Species richness abundance or number of individuals of the different species 
• • Tropical areas have greater species richness since it can support more life
• • Species evenness, number of individuals of the different species making up a community (Miller & Spoolman, 2009).
  • proportion or relative abundance of each species
• • if the number of individuals vary there is a greater diversity, hence low species evenness can be observed
• • A community where the number of individuals of the different species are nearer to each other has a higher species evenness than one where there are much more of some species compared to others.
• True or False: Most species are, thus, moderately abundant (True)
• • A tropical forest has a large number of different species but generally have few individuals of each species.
• • A coniferous forest may have only small number of species but a large number of each species.
• Coniferous forest has low species richness and high species evenness
• Tropical forest has high species richness and low species evenness
• Microenvironments has many niches. If there are many niches, it has many species that occupy the area.
• • Environmental heterogeneity
  • One of the most important factors in species diversity
  • It means more resources, more niche and more refuges.
• • Robert MacArthur 
  • one of the first ecologists to quantify the relationship between environmental heterogeneity and species diversity. 
• • Robert MacArthur and John MacArthur (1961) 
  • studied vegetative communities ranging from grasslands to mature deciduous forests. 
  • They found out that plant communities with greater foliage height diversity supported more diverse bird communities
• • Foliage height diversity increases with species richness and species evenness
  • species richness
  • which determines the number of vegetative layers 
  • species evenness
  • how evenly vegetative biomass of different tree species is distributed among layers
• • Foliage height diversity increases with species richness and species evenness
  • species richness
  • which determines the number of vegetative layers 
  • species evenness
  • how evenly vegetative biomass of different tree species is distributed among layers
• • For plants, variation in physical and chemical  conditions, such as temperature, moisture and availability of soil nutrients contribute to environmental complexity. 
  • Inverse relationship in plants
  • More fertile soil has less species compared to soil that has less nutrients. 
  • In less fertile soil, it has more plants but it is less competitive compared to those in fertile soil that has a dominant plant that is more competitive. 
• • Huston (1979)
  • examined the relationship between species richness and soil fertility (percentage of phosphorus, potassium and calcium) in 46 sites in tropical rainforests in Costa Rica
  • found an inverse relationship between species richness and soil fertility.
  • More fertile soils supported a smaller number of tree species than soils with less nutrients available.
• • Tilman et al. (1982)
  • conducted an experiment similar to Gause’s on competition between two Paramecium species.
  • Tilman grew two species of diatoms: Cyclotella meneghiniana and Asterionella formosa
  • The implication of this finding is that if the silicate:phosphate ratios vary across a lake, then there is higher environmental heterogeneity that influences species diversity of diatoms and their consumers (Molles, 2013).
• • Physical structure of a community 
  • refers to the pattern of spatial distribution of individuals and species in a community (Cunningham and Cunningham, 2007). 
• • Zonation (Smith and Smith, 2009).
  • The changes in the physical and biological structures of communities as one moves across the landscape.
• • Trophic structure
  • refers to the feeding relationships among the species of a community
  • these relationships are summarized in a food web
• • food web
  • formed by several simple, straight-line food chains that are shown as interconnected in a diagram
• • Basal species
  • species that do not feed on other organisms but are fed upon by other organisms
• • Intermediate species
  • feed on the other species and are also fed upon by other species
• • Top predators 
  • feed on intermediate and basal species and do not have predators (Smith and Smith, 2009).
• • Keystone species
  • great importance to food web
• • Guilds
  • Organisms that obtain the same general kind of food depending on the way they feed.
• ToF: Members of a guild belong to different species and even kingdoms but they obtain food in similar ways (True)
• • Functional Types
  • Classifying organisms in a community based on their responses to the environment or role in the community rather than taxonomy.
• • Photosynthetic pathway
  • C3
  • C4
  • CAM
• • Adaptations to light
  • Shade-tolerant
  • Shade-intolerant
• • Timing of reproductive effort
  • Semelparous
  • Iteroparous
• • (Paine) The species with the strongest influence on the community structure as the keystone species.
• • One of the most commonly introduced groups of organisms are fish.