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Species - a group of individuals that is able to breed with each other Population - any group of organisms of the same species in a particular space Community - a group of organisms living in a given area, an assemblage of populations of different species living close enough for potential interactions Characterizing and describing communities requires us to focus on the distribution and abundance of different species that exist as recognizable ecological units. • “Community” as a spatial concept - depends a lot on researcher’s perception of environmental variability 1 Factors that influence community development: • physical habitat - light, temperature, moisture • chemical environment - pH, nutrients • biotic interactions - either with other individuals of the same species or with other species Types of biotic interactions: Intraspecific interactions between members of the same population (= population dynamics) Interspecific interaction between populations of different species living together (= community dynamics) 2 Interaction type Description Neutralism Predation (includes herbivory) Neither population affects the other. One organism uses another for a food source. Predator (pop. 1) usually larger than prey (pop. 2) Parasatism Competition Population 1 Population 2 0 + 0 - One species benefits while the other is harmed (though usually not killed). Parasite (pop. 1) usually smaller body size than the host (pop. 2). + - Occurs within or between species that share a limiting resource. Negative affect on both populations. - - Amensalism Commensalism One species is harmed or inhibited by the other. Benefitial to population 1 (the commensal) but neutral or of no benefit to population 2. + 0 or + 0 Protocooperation Both species benefit, not required for existence. + + Mutalism Both species benefit, obligatory relationship. + + orange text = antagonistic interactions green text = beneficial interactions Parasitism: a relationship between two species in which one benefits (parasite) at the expense of the other (host). a parasite draws nourishment from the live body of another species e.g. fleas, ticks, tapeworms, aphids, mistletoe, most fungal and bacterial infections/diseases 3 Predation: also relationship between two species in which one benefits (predator) at the expense of the other (prey). a predator draws nourishment from the dead/killed body of another species. e.g. herbivory, lion attacking a deer, hawk feeding on a sparrow Big Problem with Introduced and Invasive Species Normally, host & parasite and prey & predator have co-evolved … • host/prey has some measure of defense against the parasite/predator • parasite/predator not as virulent and lethal so as to either not kill off the host or to not so drastically reduce the numbers of prey that they disappear altogether (much more so for specialist, less so for generalists). But introduced and invasive species are especially virulent and destructive because they usually co-evolved elsewhere with a different set of defenses and attacks with similar related host/prey species, but the “new” hosts/prey never evolved those defenses and get “taken out” much more effectively, sometimes to the point of extinction. • Chestnut blight and Hemlock wooly adelgid (from Asia to E. USA) • Brown tree snake (from Solomon Islands, New Guinea, N. & E. Australia, E. Indonesia to Guam and other Pacific Islands) • Cane Toads (from Cuba and Caribbean to Brisbane and Florida) • Gypsy Moths (Asia & Europe to US) • Rabbits (and Myxomatosis via mossies and intro’d fleas) in Australia • Kudzu 4 Model of the vegetation-herbivore-predator cycle involving the snowshoe hare and lynx. Competition: any interaction that is mutually detrimental to both participants, within or between species that share limited resources e.g. • Lions and hyenas competing for zebra carcasses • Animals competing for foraging territories and breeding and nesting/denning sites * Fast growing trees intercept light and shade out plants beneath their canopy ** Bigger trees with larger root systems taking up relatively more water than smaller understory trees with smaller root systems * Asymmetrical competition ** Symmetrical competition 5 Competition can be: intraspecific - between members of the same species / population interspecific - between different populations of different species competition occurs when 2 or more groups use the same limiting resource (e.g. food, water, space, light) Competition is density dependent when more organisms desire a limited resource, competition for it is more intense. the more similar the requirements of the two groups (the more similar their niches), the more intense the competition. This can lead to the mutual exclusion of competing species, instead of coexistence. 6 The ecological niche: fundamental role an organism plays in a community what does an organism do? what does an organism require to survive? what is its relationship to food and enemies, etc. ? “Niche” describes the way an organism interacts with all the biotic and abiotic factors in the environment. “functional niche” – what it does in the ecosystem “resource niche” – what it requires Niche overlap: what happens if two or more species use a portion of the same resource (e.g. food) simultaneously? = more intense competition Competitive exclusion principle: “Complete” overlap cannot occur two species with identical needs for the same limiting resources cannot coexist in the same place 7 Outcome of competitive exclusion: 1. Extinction 2. Habitat restriction / Resource partitioning 3. Character displacement — phenological changes in the morphology of individuals in the population depending on whether or not the competitors are typically present or not. 1. Extinction Two species of paramecium in direct competition both do not persist. 100 P. aurelia (alone) P. aurelia (mixed) 80 P. caidatum (alone) 60 40 20 0 P. caidatum (mixed) 0 2 4 6 8 10 12 14 16 18 Time (days) 8 2. Habitat restriction/ Resource partitioning: Feeding zones in a spruce tree of 5 species of warbles. Cape may warbler Yellow rumped warbler Black throated warbler Bay breasted warbler Blackburnian warbler Partitioning of the soil resource by a group of desert plants, different root systems develop to minimize competition for water. 9 Spatial zonation based on environmental tolerances and competitive ability 3. Character displacement: Beak sizes of ground finch, different beak morphologies allow the two populations to consume different foods. 10 Commensalism: a relationship between two species that is beneficial to one, but neutral or of no benefit to the other. e.g. epiphytes (plants that grow on the branches of trees) - they depend on the tree for support only, their roots draw nutrients from the humid air. Protocooperation: a relationship between two populations where both benefit association is not required for either to survive e.g. sea anemones sometimes take up residence on the back of a hermit crab’s shell 11 Mutualism: a relationship between two species where both benefit. continued association is required for either to survive. e.g. termites and bacteria (in termite guts) lichens (blue-green algae and fungi) Diversity or Biodiversity describes complexity of interactions in a community composed of: richness - number of species in a community evenness - compares the relative abundance of different community members 12 Community 1: 25 A 25 B 25 C 25 D Community 2: 97 A 1B 1C 1D equal richness (same number of members) different relative abundances (evenness) Stability absence of fluctuation in a system Resistance and Resiliency ability of a system to resist change or to recover rapidly after a disturbance Some ecosystems may be very stable due to lack of disturbance or because it takes a relatively big strong disturbance to push the m out of equilibrium and to have any significant effect (= hi resistance), BUT once sufficiently disturbed they may have very little ability to quickly recover (if at all) back to the original state (= lo resiliency). Other ecosystems may be less resistant but more resilient. 13 14