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Transcript
14.1 Habitat And Niche Ecological niches Niches: fundamental and realized Principle of competitive exclusion Realized niche as competitive refuge Niche crossovers Character displacement Adaptive radiation 14.1 Habitat And Niche Ecological niche concept Habitat occupance = Ecological niche = “Where are you from?” “What’s your address?” “What do you do?” “Do you eat meat?” 14.1 Habitat And Niche Specialized habitat occupance 14.1 Habitat And Niche Niche breadth: generalist vs. specialist 14.1 Habitat And Niche Categorizing niches Niche overlap? Junco Chickadee Douglas squirrel Deer mouse Deer Coyote Cougar Main food source seeds seeds & insects seeds seeds generalist/ specialist ? specialist ? generalist ? specialist ? specialist 14.1 Habitat And Niche The principle of competitive exclusion “Two species requiring approximately the same resources are not likely to remain long evenly balanced in numbers in the same habitat. ” J. Grinnell (1915) Also known as “Gause’s principle” after mathematical formulation by Gause in 1930. In consequence, the loser is excluded, at least locally, unless… 14.1 Habitat And Niche 1. There are refuges from competition; the potential loser hangs on in marginal habitats; or 2. The loser can re-immigrate from elsewhere; or 3. Disturbances in the environment prevent the winner from gaining a complete monopoly. 14.1 Habitat And Niche Categorizing niches: dietary segregation amongst local granivores Species Habitat Other foods? thrush floor berries, insects (esp. ants and beetles) warbler canopy insects Dusky squirrel canopy insects, mushrooms, flowers, birds’ eggs mouse floor insect larvae (esp. moths) 14.1 Habitat And Niche Reducing niche overlap through habitat segregation upper canopy lower canopy shrub floor resource overlap? 14.1 Habitat And Niche Fundamental vs. realized niche 14.1 Habitat And Niche Flour Beetle Experiments • • What’s a niche? Collective environmental factors that influence growth, survival, and reproduction. Tribolium beetles infest stored grain products. – Park studied interspecific competition between T. confusum and T. castaneum under varied environmental conditions. Had similar fundamental niches; when grown alone the abiotic constraints were similar. Growing the two species together suggested interspecific competition restricts the realized niches (adds biotic influences) of both species to fewer environmental conditions. 14.1 Habitat And Niche Competition and Niches of Small Rodents • Brown studied competition among rodents in Chihuahuan Desert. – Predicted if competition among rodents is mainly for food, then small granivorous rodent populations would increase in response to removal of larger granivorous rodents. Insectivorous rodents would show little or no response. Results supported hypothesis. 14.1 Habitat And Niche Competition and Niches of Small Rodents 14.1 Habitat And Niche Niche compression Realized niches are narrower than fundamental niches, therefore the species occupies a narrower range of habitats than it would in the absence of competition. The realized niche can be regarded as a ‘competitive refuge’. 14.1 Habitat And Niche Determining niche compression Natural experiments Allopatric speciation results when a population is separated by a physical barrier (geographic speciation) . Sympatric speciation occurs without physical separation of members of the population. compression 14.1 Habitat And Niche Niche compression: barnacles on Scotland’s rocky shores 14.1 Habitat And Niche Overlap andNiche Competition Between Barnacles • Connell discovered interspecific competition in barnacles. Balanus plays a role in determining lower limit of Chthamalus within intertidal zone. – Did not account for all observed patterns. 14.1 Habitat And Niche Sedge niches: Fraser delta high tide low tide Daily Inundation Rare H1: realized = fundamental Daily Inundation Rare H2: Scirpus occupies refuge 14.1 Habitat And Niche Determining niche compression A. Field experiments: reciprocal transplants high tide low tide Two-year transplant experiment was inconclusive. Both species grew well in other species zone. (Mike Pidwirny) 14.1 Habitat And Niche Dominance hierarchy dominant sp. subdominant sp. in the absence of competition resource gradient A B C with competition refuge exclusion refuge zone resource gradient 14.1 Habitat And Niche Character displacement 14.1 Habitat And Niche Character Displacement = evolution of niche divergence by competition • • • The degree of competition is assumed to depend upon degree of niche overlap, Interspecific competition has been predicted to lead to directional selection for reduced niche overlap. Galapagos finch size versus seed size. 14.1 Habitat And Niche Galapagos Finch Character allopatric Displacement sympatric 14.1 Habitat And Niche Character Displacement • Taper and Case: Necessary criteria for C.D.: – Morphological differences between sympatric populations are statistically greater than differences between allopatric populations. – Differences between sympatric and allopatric populations have genetic basis. – Differences between sympatric and allopatric populations evolved in place, and are not derived from different founder groups already differing in the character. 14.1 Habitat And Niche Taper and Case: Characteristics – Variation in the character must have a known effect on use of resources. – Must be demonstrated competition for the resource and competition must be directly correlated with character similarity. – Differences in character cannot be explained by differences in resources available to each of the populations. 14.1 Habitat And Niche Placental mammals Does evolution fill a finite number of jobs? (e.g. community wants burrower?) Is there a restricted “guild”? Australian marsupials 14.1 Habitat And Niche “woodpecker” “nectar-feeder” Hawaiian honeycreepers: seed-eating finch evolves into vacant niches? http://biology.swau.edu/faculty/petr/ftphotos/hawaii/postcards/birds/ 14.1 Habitat And Niche Galapagos finches: opportunistic evolution Source: Lack, D. 1966. Darwin’s Finches. Harper, N.Y. 14.1 Habitat And Niche Parallel (or convergent) evolution of animals inhabiting African (right) and S. American (left) tropical forest 14.1 Habitat And Niche Island invasions and community saturation: plants New Zealand ~2000 native plants ~2000 naturalized aliens 3 natives extinct California ~5000 native plants ~1000 naturalized aliens <30 natives extinct Brown, JH and Sax, DF 2004. Austral Ecology 29, 530-536. 14.1 Habitat And Niche Island invasions and community saturation: fish Hawaii 5 native freshwater fish species 40 naturalized aliens no extinctions 124 watersheds in temperate North America Fish diversity increased in 100; declined in 20 Brown, JH and Sax, DF 2004. Austral Ecology 29, 530-536. 14.1 Habitat And Niche What is a “community”?* An ecological (or biological) community refers to a group of interacting organisms living together in a specific geographical area or habitat. An equivalent (and now somewhat anachronistic) term is biocenosis (proposed by Karl Möbius in 1877 to describe the interacting organisms of the oyster- and mussel-bearing tidal flats of the North Sea). *or is it a “commutiny”? 14.1 Habitat And Niche Community structure Closed vs. open communities Ecotones (community boundaries) The continuum concept Biogeoclimatic zones 14.1 Habitat And Niche Are communities closed, or open? *community named after dominant(s): e.g. Douglas fir, hemlockcedar. * * * E = ecotone fidelity? = a continuum? 14.1 Habitat And Niche Characteristics of open and closed communities Early proponent OPEN H.A. Gleason CLOSED F.E. Clements Organization Individualistic Holistic Boundaries Diffuse Distinct Species ranges Independent Coincident Coevolution Uncommon Prominent 14.1 Habitat And Niche Terrestrial biomes (plants and animals) 14.1 Habitat And Niche KEY CONCEPT Every organism has a habitat and a niche. 14.1 Habitat And Niche Objectives • Differentiate between a habitat and a niche • Differentiate between competitive exclusion and ecological equivalents 14.1 Habitat And Niche A habitat differs from a niche. • A habitat is all aspects of the area in which an organism lives. – biotic factors – abiotic factors • An ecological niche includes all of the factors that a species needs to survive, stay healthy, and reproduce. – food – abiotic conditions – behavior 14.1 Habitat And Niche Resource availability gives structure to a community. • Species can share habitats and resources. • Competition occurs when two species use resources in the same way. • Competitive exclusion keeps two species from occupying the same niche. 14.1 Habitat And Niche • Competitive exclusion has different outcomes. – One species is better suited to the niche and the other will either be pushed out or become extinct. – The niche will be divided. – The two species will further diverge. 14.1 Habitat And Niche • Ecological equivalents are species that occupy similar niches but live in different geographical regions. Madagascar South America 14.1 Habitat And Niche What are the 3 parts of an organisms ecological niche? • Food type • Abiotic conditions • Behavior 14.1 Habitat And Niche What does the principle Competitive Exclusion say will happen when 2 species compete for the same resource? • One species will be better suited to the niche, and the other species will either be pushed into another niche or become extinct 14.1 Habitat And Niche If a group of mantella frogs were transported to the ecosystem of the poison dart frogs, what might happen to the 2 species populations? • As ecological equivalents, they share a similar niche. • The population better suited to the niche might deprive the other of resources, causing the other to die off. OR • One population might respond to limitted resources by altering its niche. 14.1 Habitat And Niche A bison and an elk live in the same habitat and feed on the same grasses. Does this mean that the competitive exclusion principle does not apply? Expleain. • The competitive exclusion principle only applies if the 2 species live in the same habitat AND occupy the same niche • A niche includes – Food type – Abiotic conditions – Behavior • These two species use the same food resource but occupy different niches 14.1 Habitat And Niche Considering the competitive exclusion principle, why may it be harmful to transport a species such as a rabbit, to another habitat where it currently does not exist? • If a new species is introduced to an area, it may occupy a similar niche as a native species and be better adapted for the niche to have no natural predators. • This could drive the native species to extinction 14.2 14.1 Habitat And Niche KEY CONCEPT Organisms interact as individuals and as populations. 14.2 14.1 Habitat And Niche Objectives • Compare & Contrast interspecfic and intraspecific competition • Describe the 3 types of symbiosis 14.2 14.1 Habitat And Niche Competition and predation are two important ways in which organisms interact. • Competition occurs when two organisms fight for the same limited resource. – Intraspecific competition – Interspecific competition 14.2 14.1 Habitat And Niche • Predation occurs when one organism captures and eats another. 14.2 14.1 Habitat And Niche • There are three major types of symbiotic relationships. – Mutualism: both organisms benefit 14.2 14.1 Habitat And Niche • There are three major types of symbiotic relationships. – Commensalism: one organism benefits, the other is unharmed Ø Human Our eyelashes are home to tiny mites that feast on oil secretions and dead skin. Without harming us, up to 20 mites may be living in one eyelash follicle. Commensalism Ø Organism is not affected + + Organism benefits Demodicids Eyelash mites find all they need to survive in the tiny follicles of eyelashes. Magnified here 225 times, these creatures measure 0.4 mm in length and can be seen only with a microscope. 14.2 14.1 Habitat And Niche • There are three major types of symbiotic relationships. – Parasitism: one organism benefits, the other is harmed 0 Parasitism + _ Hornworm caterpillar The host hornworm will eventually die as its organs are consumed by wasp larvae. _ Organism is not affected 0 Braconid wasp Braconid larvae feed on their host and release themselves shortly before reaching the pupae stage of development. Organism benefits 14.2 14.1 Habitat And Niche • There are three major types of symbiotic relationships. – Parasitism meet their needs as ectoparasites (such as leeches) and endopaasites (such as hookworms) 14.2 14.1 Habitat And Niche During the fall spawning of salmon, grizzly bears fight over space on the banks of a river. What type of competition is this? • The bears are fighting amongst themselves so it is considered intraspecific competition 14.2 14.1 Habitat And Niche Describe and give an example of the 3 types of symbiosis • Mutualism +/+ • Commensalism +/0 • Parasitism +/- 14.2 14.1 Habitat And Niche How are predation & parasitism similar? How do they differ? • Predation & parasitism are both relationships in which one organism benefits while the other is harmed. • In predation, the predator needs to kill its prey in order to benefit • In parasitism, the parasite benefits by keeping its host alive 14.2 14.1 Habitat And Niche After a lion has made a kill birds will sometimes arrive to pick at the carcass. The birds would be considered _________(A)_________________ while the lions would be considered _________(B)_____________________ • A) Scavengers • B) Predators 14.3 14.1 Habitat And Niche KEY CONCEPT Each population has a density, a dispersion, and a reproductive strategy. 14.3 14.1 Habitat And Niche Objectives • Consider density and geographic dispersal as characteristics of populations • Describe 3 basic types of survivorship curves in relation to reproductive strategies. 14.3 14.1 Habitat And Niche Population density is the number of individuals that live in a defined area. • Population density is a measurement of the number of individuals living in a defined space. • Scientists can calculate population density. 14.3 14.1 Habitat And Niche Geographic dispersion of a population shows how individuals in a population are spaced. • Population dispersion refers to how a population is spread in Clumped an area. dispersion Uniform dispersion Random dispersion 14.3 14.1 Habitat And Niche • There are three types of dispersion. – clumped 14.3 14.1 Habitat And Niche • There are three types of dispersion. – uniform 14.3 14.1 Habitat And Niche • There are three types of dispersion. – random 14.3 14.1 Habitat And Niche Survivorship curves help to describe the reproductive strategy of a species. • A survivorship curve is a diagram showing the number of surviving members over time from a measured set of births. 14.3 14.1 Habitat And Niche • Survivorship curves can be type I, II or III. – Type I—low level of infant mortality and an older population – common to large mammals and humans – Type II—survivorship rate is equal at all stages of life – common to birds and reptiles – Type III—very high birth rate, very high infant mortality – common to invertebrates and plants 14.3 14.1 Habitat And Niche An Organism has 10 offspring. Two of these offspring die each year over a 5 year period. Is this organism more likely to be a bird or insect? Explain. • The organism is a bird because the mortality pattern described is closest to type II. • Insects tend to be type III, with many offspring and high mortality early in life stages 14.4 14.1 Habitat And Niche KEY CONCEPT Populations grow in predictable patterns. 14.4 14.1 Habitat And Niche Objectives • Describe 4 characteristics that affect population size • Compare exponential and logistic population growth • Identify factors that limit population growth 14.4 14.1 Habitat And Niche Changes in a population’s size are determined by immigration, births, emigration, and deaths. • The size of a population is always changing. • Four factors affect the size of a population. – immigration – births – emigration – deaths 14.4 14.1 Habitat And Niche Population growth is based on available resources. • Exponential growth is a rapid population increase due to an abundance of resources. 14.4 14.1 Habitat And Niche • Logistic growth is due to a population facing limited resources. 14.4 14.1 Habitat And Niche • Carrying capacity is the maximum number of individuals in a population that the environment can support. • A population crash is a dramatic decline in the size of a population over a short period of time. 14.4 14.1 Habitat And Niche Ecological factors limit population growth. • A limiting factor is something that keeps the size of a population down. • Density-dependent limiting factors are affected by the number of individuals in a given area. 14.4 14.1 Habitat And Niche • Density-dependent limiting factors are affected by the number of individuals in a given area. – predation – competition – parasitism and disease 14.4 14.1 Habitat And Niche • Density-independent limiting factors limit a population’s growth regardless of the density. – unusual weather – natural disasters – human activities 14.4 14.1 Habitat And Niche What 4 factors determine the growth rate of a population? • Immigration • Births • Deaths • Emigration 14.4 14.1 Habitat And Niche How does carrying capacity affect the size of a population? • Carrying capacity limits the size of a population 14.4 14.1 What Habitat And Niche is the main difference between a densitydependant limiting factor and a density-independent limiting factor? Give an example of each. Density-Dependant • A density dependant limiting fact is affected by the number of individuals in a given area – These are usually BIOTIC limiting facto=rs such as Predation Competition Disease Density-Independant • A density independent limiting factor is not affected by population size/density – These are usually ABIOTIC limiting factors such as Weather Forrest fires Natural disasters Human activities 14.4 14.1 Habitat And Niche What might cause exponential growth to occur only for a short period when a new species is introduced to a resource filled environment. • Eventually, the growing population will consume all the resources, and the species may experience a population crash. 14.4 14.1 Habitat And Niche Give an example of how a symbiotic relationship could cause a population to crash. • If a parasite or disease spreads in a dense population, it could cause a population to decline dramatically over a short period of time. 14.5 14.1 Habitat And Niche KEY CONCEPT Ecological succession is a process of change in the species that make up a community. 14.5 14.1 Habitat And Niche Objectives • Describe the process of primary succession • Explain the difference between primary and secondary seuccession 14.5 14.1 Habitat And Niche Succession occurs following a disturbance in an ecosystem. • Succession regenerates or creates a community after a disturbance. – a sequence of biotic changes – damaged communities are regenerated – new communities arise in previously uninhabited areas 14.5 14.1 Habitat And Niche • There are two types of succession. – primary succession — started by pioneer species 14.5 14.1 Habitat And Niche • There are two types of succession. – secondary succession — started by remaining species 14.5 14.1 Habitat And Niche How is primary succession different from secondary succession? • Primary succession begins with barren rock, worn down and colonized with a pioneer species • Secondary succession begins with established soil in which many different plants can grow 14.5 14.1 Habitat And Niche Why are pioneer species so important for primary succession? • Pioneer species such as mosses and lichens can break down rock into smaller pieces. • When they die, their remains may mix with the pieces of rock forming a thin layer of soil • They change the ecosystem in ways that enable the support of more diverse species 14.5 14.1 Habitat And Niche Does the process of primary succession take longer in the tropical or arctic areas? Explain. • Primary succession takes longer in arctic areas because – rock is covered in snow part of the year – the growing season is shorter – and cold temperatures slow growth and decomposition • Soil takes much longer to form. 14.5 14.1 Habitat And Niche Which reaches a climax community 1st, an area undergoing primary or secondary succession? Explain • Secondary succession takes less time to reach a stable climax community because the soil is already there • In primary succession there is no soil and so it will take longer to reach a climax community 14.5 14.1 Habitat And Niche During succession, what might be the limiting factor for sun-loving mosses as taller plants begin to grow? • The amount of sunlight that reaches them 14.5 14.1 Habitat And Niche At what point during primary succession does an ecosystem provide the fewest habitats for an organism? Explain. • There are no habitable areas in the earliest stages of succession because there is no soil to support producers.. • Land becomes habitable once rock has weathered enough to support mosses and lichens • Over time mosses and lichens will provide the resources needed to support other organisms 14.1 Habitat And Niche Redwood forest niches 14.1 Habitat And Niche Competitive ‘release’ or are niches and habitat occupancy moreor-less fixed? NB: hypothetical !
