Lecture 21: Ecological Niche PDF

Lecture 21. Ecological Niche Species interactions & ecological niche Each species in a community occupies a specific ecological niche Species’ ecological niche determines how it will interact with other species Ecological Niche: the full range of environmental conditions (biotic & abiotic) under...

Lecture 21. Ecological Niche Species interactions & ecological niche Each species in a community occupies a specific ecological niche Species’ ecological niche determines how it will interact with other species Ecological Niche: the full range of environmental conditions (biotic & abiotic) under which a species can exist. Species’ niches are affected by many factors – abiotic & biotic. living thing marlining Architectural niche: recess or cavity in a wall that holds a statue, vase, etc. Statues in niches in Gothic cathedral Factors that can determine ecological niche: Time of day active (nocturnal or diurnal) Prey availability Soil chemistry Presence of water pH of water Salinity of water Temperature range Precipitation & humidity Elevation Vegetation type Presence of predators or parasites Presence of prey or hosts Availability of shelter or nesting sites Availability of nesting material Etc. Niche characteristics of American Dipper: Fast-flowing mountain streams Streams have cascades & riffles Streams are unpolluted Streambeds with cobbles or coarse gravel Midstream or streamside boulders or large woody debris Waterway ice-free in winter Aquatic insects, insect larvae, small fish, fish eggs Vertical surface over rushing water – like stream bank Presence of moss American Dipper video Niche characteristics of American Dipper Niche characteristics of American Dipper Ecological niche is not a location or a habitat Habitat – geographic area or region with specific abiotic & biotic - characteristics in which organisms live Photo: oak savannah habitat Hutchinson’s niche concept – mathematical model of niche Niche = n-dimensional hypervolume dimension = factor (axis on graph) n = hypothetical number of factors that determines organism’s niche Niche graph on right has 3 dimensions : temperature, elevation, latitude Species’ niche is a set of conditions and resources Example: niche (‘niche space’) of hypothetical species defined by 2 factors: temperature & food availability If ranges of temperature & food availability both fall within red oval, the conditions are suitable for the species. Note: other factors would also contribute to the niche of this species Mott 2010 Example: niche (‘niche space’) of a hypothetical species defined by 3 factors: temperature, elevation, & latitude Niche defined using 3 factors (n = 3): temperature, elevation, & latitude Total niche of species = multidimensional ‘niche space’ defined by multiple biotic & abiotic factors  Full actudfull) Fundamental niche vs. realized niche Fundamental Niche: full range of environmental conditions (biotic & abiotic) under which a species can exist. Fundamental Niche: full range of environmental conditions (biotic & abiotic) under which species can exist. Realized Niche: range of environmental conditions that species actually occupies If requirements of different species overlap, their niches overlap Niche overlap between species causes competition Fundamental Niche vs. Realized Niche Realized niche is the fraction or subset of fundamental niche that a species actually occupies due to interactions with other species. Which interactions with other species are causing this hypothetical fish species to occupy its realized niche rather than its fundamental niche? Connell’s barnacles – fundamental vs. realized niche Balanus & Chthamalus: 2 species of barnacles that live attached to rocks in the rocky intertidal ecosystem Chthamalus Balanus Connell’s experiments: When Balanus was removed, distribution of Chthamalus moved down the rocks When Chthamalus was removed, distribution of Balanus did not change An ecological community is made up of species with varying levels of overlap in their ecological niches. Level of overlap in niches helps determine if & how species interact Georgii Gause & Competitive Exclusion In the lab environment, Gause simplified the niche of each species Each species had one need: food Niches of the two species overlapped completely Competitive Exclusion Principle Niches of the two species overlapped completely – competing for same limited food source Effect: one species (P. caudatum) always went extinct P. aurelia was a better competitor – it acquired resources more efficiently Competitive Exclusion Principle Competitive exclusion – two species cannot occupy the same niche & coexist indefinitely – one will always outcompete the other Competitive exclusion is one possible outcome of niche overlap & competition Resource partitioning: alternative outcome of competition evolutionary change Resource partitioning (niche partitioning) – phenotypic differences evolve that allow species to use different resources  reduces competition SEED SIZE evolutionary change SEED SIZE Among shorebird species, variation in bill shape & bill length (morphology), & method of acquiring prey (behavior) allows them to partition resources. Among shorebird species, variation in bill shape & bill length (morphology), & method of acquiring prey (behavior) allows them to partition resources.  Resource partitioning – MacArthur studied feeding & nesting behavior of 5 morphologically similar warbler species that co- occurred in the same habitats in the same geographic area. ‘Myrtle’ Cape May Black-throated Green Blackburnian Bay-breasted Warbler MacArthur, R. H. 1958. Population ecology of some warblers of northeastern coniferous forests. Ecology 39: 599–619.  Cape Myrtle May Warbler Warbler Resource partitioning – 5 warbler species differed in nesting date & nesting height (height in tree) Character displacement Form of resource partitioning with a particular geographic context. Can evolve when two species with high niche overlap are sympatric (live in same area) Character displacement in Darwin’s finches – Galapagos Islands Character displacement results in a particular geographic pattern in the traits affected by selection. Character displacement in beak depth occurs between G. fulginosa & G. fortis on islands where they are sympatric Beak depth is ‘displaced’ where they are sympatric.  Niche & competition summary 1. Fundamental niche: full range of environmental conditions (biotic & abiotic) under which species can exist. 2. Realized niche: range of environmental conditions that species actually occupies due to interactions with other species. 3. Competition: use of a shared, limited resource among members of a single species (intraspecific competition) or between different species whose niches overlap (interspecific competition). 4. Intraspecific competition: affects population size by reducing amount of available resources – can cause population to reach carrying capacity 5. Interspecific competition: if 2 species compete for same, limiting resources one may become extinct locally, OR phenotypic differences may evolve between competing species that allow them to use different resources and thus reduce competition (resource partitioning)