Input Template for Content Writers. (e-text and Learn More) 1. Details of Module and its Structure

Input Template for Content Writers (e-Text and Learn More)

1.

Ecology Population Ecology Population Features

Module Detail

Subject Name <Botany>

Paper Name <Ecology>

Module Name/Title <METAPOPULATION>

Module Id

Pre-requisites <Basic knowledge about population and distribution of species on geographical gradient>

Objectives <To make students aware about properties of metapopulation and importance of metapopulation studies>

Keywords <Metapopulation>,<Metapopulationdynamics>,<Conservation >

2. Development Team

Structure of Module/Syllabus of a module (Define Topic / Sub-topic of module )

<Population> <Introduction>, <types of metapopulation>,<Metapopulation dynamics>

Role Name Affiliation

Subject Coordinator <Prof.Sujata Bhargava> Savitribai Phule Pune University

Paper Coordinator <Dr.NSR Krishnayya> MS University Baroda

Content Writer/Author (CW) <Dr. Neeta Pandya> MS University Baroda Content Reviewer (CR) <Dr. NSR Krishnayya>

Language Editor (LE) <Dr. NSR Krishnayya>

Ecology Population Ecology Population Features

TABLE OF CONTENTS(for textual content) 1. Introduction

2. Types of Metapopulation

2.1

Classical Metapopulation / LevinsMetapopulation

2.2

Mainland- Island Metapopulation /Boorman-LevittMetapopulation

Source Sink Metapopulation/Patchy Metapopulation

2.4

Non- Equilibrium Metapopulation

3.1 Models of Metapopulation Dynamics 4. Applications of Metapopulation Models

4.1 Metapopulation& Conservation

1. Introduction

Populations of many species have a patchy distribution, the most prominent reason of which is spatial heterogeneity of the habitat. It results in many small population sets’ establishment, where the sets are linked with different processes and such a group of interacting populations of the same species is known as Metapopulation. Individual population in such case is referred as a local population or deme population.The concept was proposed by an American scientist RichardLevins(1969, 1970). He defined metapopulation as a set of populations linked with significant flow of individuals.

The concept was accepted by many scientists.Hanski and Simberloff(1997) modified the definition asMetapopulation is a set of local population within some larger area where typically migration from one local population to at least some other patch is possible. Metapopulations occur naturally as well as are created as a result of human actions.The population and Metapopulation can be differentiated as on the basis of heterogeneity in the area. A population occupies a patch with one set of microclimatic condition while metapopulation comprises many such populations invading the larger area in the local environment conditions.

2. Types of Metapopulations

2.1. Classical Metapopulation / LevinsMetapopulation:It has a large network of similar small patches with local dynamics occurring at a much faster rate than the metapopulation dynamics. This metapopulation indicates higher risk of extinction at all the local population sets.

2.2. Mainland- Island Metapopulation / Boorman- Levitt Metapopulation: This defines a system of habitat patches located within dispersal distances from a very large habitat patch, the large patch behaves as mainland (source population ) from where dispersal to small island patches (sink populations) is possible.

Source populations produce excess individuals that emigrate to other patches and Sink populations are maintained by immigration into unfavorable habitats, in this type of system the local population never goes extinct andit is an ideal population type.

2.3. Source Sink Metapopulation/Patchy Metapopulation: It is a system where sub populations have much low density and may show negative growth in absence of dispersal and positive growth in presence of dispersal. Thus every patch can function as Source as well as Sink.

Ecology Population Ecology Population Features

2.4. Non- Equilibrium Metapopulation: It is a system in which long term extinction rates exceed colonization rates or vice -versa. Populations are isolated and communication among patches is highly diffused, such metapopulationis athighrisk of extinction.

Fig.1. Different types of Metapopulation Models

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Source:

3.Metapopulation Dynamic.

As in population, birth and death rates play important role in population growth, thethree key processes which are important in Metapopulation dynamics are colonization, extinction and turnover.Metapopulations are characterized by repeated extinctions and colonization. Extinction occurs in already occupied area while Colonization is possible in already occupied area and in vacant area which is suitable for the species growth.

Extinction:It is the disappearance of a species. It starts with thinning of population and then ultimate disappearance of the population. The causal processes for extinction are high mortality rate, low natalityrate poor immigration, high emigration and low resilience to fluctuation and the distribution of species. The response of the species varies, the threat is more too rare and endemic species as compare to wide spread species. In metapopulation dynamics extinction is usually a constant risk at occupied patches.

Colonization: It is the appearance and establishment of a species at a patch.It depends on number of occupied and vacantpatches. Colonization is affected by the proximity of the mainland and process of migration / dispersal.

Turnover: Turnover is related to extermination of local populations and establishment of new local populations in vacant habitat patches by nomad from existing local populations.It is process of reappearance.

Ecology Population Ecology Population Features

3.1.Models of Metapopulation Dynamics

Metapopulation models are important tools for understanding dispersal and spread of a species on large spatial scale. These models incorporatewith local population dynamics in-between population processes like immigration, extinction and colonization and thus help in linking population ecology with biogeography.

Metapopulation model was firstintroduced byLevins (1969, 1970), He assumed that:

 Infinite numbers of identical habitat patches for a species exist in an area.

 All these patches have an equivalentpossibility of receiving colonists and at the same time all patches have an equal chance of extinction too.

 Once a patch is colonized, its population increases to its carrying capacity more rapidly than the rates of colonization and extinction.

The model equation is

dP/dt = C – EordP/dt = cP(1 - P) - eP, where

P = fraction of currently occupied patches dP/dt = Rate of change of P

C = Colonization rate per empty patch E = Extinction rate per occupied patch

c = probability of colonization per empty patch e = probability extinction rate per occupied patch

The rate of change of P i.e. dP/dt, determines whether P will increase, decrease or stay the same (if dP/dt> 0,

<0 or =0). The rate dP/dt is given by the difference between colonization rate C and extinction rate E. In this model, colonization rate depends on the quantity of occupied patches (as sources of immigrants), as well as on the number of vacant patches (1 - P). If this is low, there are few patches available for colonization.

Extinction rate only depends on P, the proportion of populations that can become extinct. At equilibrium dP/dt = C - E = 0. For persistence of the metapopulation it is essential that c> e. In other words, as long as the probability of a patch to be colonized exceeds its probability to get extinct, the metapopulation exists, with a single stable equilibrium incidence P'(equilibrium fraction).Levins worked with fast-growing insect populations, where density rapidly becomes resource or site-limited and his model is a two state model (colonization &extinction).

Hanski (1985) developed the metapopulation approach further, by assuming that extinction rate is a quadratic function of P. He explored the feedback relationship between the fraction of patches occupied and the probability of local extinction. In his model, E also decline when there is aboost in immigration .As additional patches are occupied, the possibility to go extinct reduces. This is due to the "rescue effect", as immigration from several populated patches inclined to prevent local extinction by immediate recolonization.

The rescue effect is acrucialand probably realistic addition to Levin’s model.

Ecology Population Ecology Population Features

Fig. 2. Reaction of the rate of change dP/dt againstrate P, as the difference between colonization rate C and extinction rate E.Arrows signify areas where P elevates or decline (dP/dt> 0 or < 0) until an equilibrium is reached. (A) Levins' model, showing two functions of C with a stable equilibrium at 0 <

P' < 1 and P = 0, respectively; (B) Hanski's model, where P' is either 1 or 0.

(Source: http://www.bgu.ac.il/desert_agriculture/Popecology/PEtexts/Image22.gif)

Gotelli (1991) added another valuable concept to metapopulation theory with the assumption that immigration is not coupled with regional occurrence and is dependent only on number of unoccupied sites,there is a constant propagule rainwhich may come fromoutside, from long lived seed bank or from dormant vegetative propagules. This creates colonization rate independent of P, in island - mainland systems.

The grouping with the two prior models are shown in Fig. 3: If both C and E are linear functions of P (Fig.

3A), then P' = c /(c + e). If c = e then P' = 0.5 (instead of 0 in Levins' model). A propagule rain combined with Hanski's model (Fig. 3B), P also has a positive equilibrium, P' = c/e. If e is very low, P' = 1.

Fig. 3. Metapopulation models integrate a propagule rain (linear interaction between C and P, Gotelli 1991), (A) without the rescue effect and (B) with the rescue effect. In this models two C and E amalgamation are shown, giving different equilibrium values P'. Arrows indicate the direction of

change if dP/dt>0 or < 0.

(Source: http://www.bgu.ac.il/desert_agriculture/Popecology/PEtexts/Image23.gif)

Ecology Population Ecology Population Features

Using these models to predict how many populations a metapopulation will contain, requires a great amount of information on the associations of occurrence P, with C and E, the immigration/colonization and extinction rates.

4.Applications of Metapopulation ModelsMetapopulation studies are related with many other branches of ecology, the suggested models have their implications at many places.The important areas are island biogeography, landscape ecology and most important one the conservation biology.

4.1. Metapopulation& Conservation:Metapopulation models have been essential to the management of many species.Many species live in naturally heterogeneous or artificially fragmented landscapes, and decision on their conservation and management should consider metapopulation concepts and models (Akçakaya et al,2007). The threat of extinction is increasing by the different forces imposed on a species.

Extinction starts at a local level that means in a deme. Demes show a genetic drift due to interbreeding. It leads to homozygosity and ultimately one deme set becomes a set of homozygous individuals. Such a homozygous set will be more susceptible to any change or stress imposed on it. In such case the threat of extinction atleast at local level will rise. Therefore knowing the minimum viable population (MVP) is very important and this can be done through metapopulation study. The minimum viable population is threshold number of individuals that will ensure the persistence of sub population in any adverse condition. The size of MVP varies; the species with density dependent regulation persist for long time even with smaller MVP while the species which are affected more by environment need larger MVP for their sustenance.

Habitat destruction and fragmentationhave become major cause for metapopulation extinctions to counter this,Hanski (1997) and others have suggested a number of thumb rules, or some points to be considered in conservation and management:

1. Metapopulation will certainly become extinct, if habitat destruction continues.

2. This may take a long time, depending on the major population; there may be time to do something, such as facilitating recolonization.

3. Equilibrium conditions may never arise.

4. Several fragmentsshould be preserved partially.

5. Large numbers of suitable patches are not enough, if distances are too large, preventing recolonization and the rescue effect.

6. Distance is not the only cause affecting immigration probabilities: the properties of the terrain are crucial, including corridors and stepping stones.

7. A wide numbers of suitable patches are not adequate if they are very close together, due to possible synchronous dynamics.

8. There should be muchdivergence in local patch quality (different habitats within the range of the organism) as possible to prevent synchronous dynamics. (Not only the "best" patches.) 9. Recolonization has to be observed within a few generations for metapopulations to have a chance.

10. Sizeable patches are important, because demographic stochasticity can forced to extinction, especially in organisms with low reproductive profit.

11. Large patches are enviable; they have large populations, with numerous potential immigrants, and have high internal difference in habitat quality.

12. Patch sizes can be deceiving if negative edge effects reduce effective patch size.

Ecology Population Ecology Population Features

5.Summary Metapopulationis a set of interacting populations of a species, distributed in an area. It consists of patches which may be occupied or may remain unoccupied for some time. Processes of colonization,extinction and turn over decide the fate of metapopulation.Metapopulation dynamics can be studied through different models.These studies are intensely linked with conservation biology.

References.

1.Akçakaya, H.R., G.Mills, and C. P. Doncaster. 2007. The role of metapopulations in conservation. Pages 64-84 in Key Topics in Conservation Biology.D.W. Macdonald and K.Service, editors.Blackwell Publishing.

2.Gotelli, N.J. 1991. Metapopulation models: the rescue effects, the propagule rain, and the core-satellite hypothesis. American Naturalist 138: 768-776

3.Hanski, I. 1991. Single-species metapopulationdynamics: concepts, models, and observations. Biological Journal of the Linnean Society 42:17–38.

4.Hanski, I. 1997. Metapopulation dynamics: From concept and observations to predictive models. Pp. 69- 91. In Hanski, I. A. and Gilpin, M.E., Eds. Metapopulationbiology.San Diego, USA, Academic Press.SanDiego, Californina

5.Hanski, I., and M.Gilpin. 1991. Metapopulation dynamics: brief history and conceptual domain. Biological Journal of the Linnean Society 42:3–16.

6.Hanski, I., and D. Simberloff. 1997. The metapopulation approach, its history, conceptual domain, and application to conservation. pp. 5–26. In I. A.Hanski and M.E.Gilpin (eds.), Metapopulation Biology.

Academic Press, San Diego, Californian.

7.Levins, R. 1969. Some demographic and genetic consequences of environmental heterogeneity for biological control. Bulletin of the Entomological Society of America 15:237–240.

8. Levins, R. 1970. Extinction. pp. 77–107. In M.Gesternhaber (ed.), Some Mathematical Problems in Biology.American Mathematical Society, Providence, Rhode Island.