Chapter 40 Bio

the scientific study of the interactions between organisms and the environment

Global Ecology
The study of functioning and distributions of organisms across the biosphere and how the regional exchange of energy and materials effect them. (Examines how the regional exchange of energy and materials influence the functioning and distribution of organism across the biosphere)

the entire portion of the Earth inhabited by life; the sum of all the planets ecosystems (is the global ecosystem- the sum of all the planet’s ecosystems and landscapes)

is a group of individuals of the same species living in an area (and interbreed, producing fertile offsprings)

Population Ecology
analyzes factors that affect population size and how and why it changes through time.
the study of populations in relation to their environment including environmental influence on population density and distribution, age structure, and variations in population size (Population ecology or autoecology is a sub-field of ecology that deals with the dynamics of species populations and how these populations interact with the environment. It is the study of how the population sizes of species groups change over time and space.)

is a group of populations of different species in an area (all the organisms that inhabit that area; assemblage of population of different species living close enough together for potential interaction)

community ecology
the study of how interactions between species affect community structure and organization, examines how interactions between species (ex: such as predation and competition) affect community structure and organization

is the community of organisms in an area and the physical factors with which those organisms interact (all the organisms in a given area as well as the abiotic factors with which they interact; one or more communities and the physical environment around them) (a biological community of interacting organisms and their physical environment)

landscape ecology
the study of how the spatial arrangement of habitat types affects the distribution and abundance of organisms and ecosystem processes, focuses on the factors controlling exchanges of energy, materials, and organisms across multiple ecosystems

mosaic of connected ecosystems

organismal ecology
the branch of ecology concered with the morphological, physiclogical, and behavoiral ways in which individual organisms meretthe challanges posed by their biotic and abiotic enviroments

the long-term prevailing weather conditions in a given area (It is the most significant influence on the distribution of organisms on land and in the oceans)

four components of climate
Four physical factors that are the component of climate is temperature, precipitation, sunlight, and wind.

is climate at the global, regional, and landscape levels (general climate of the large area)

the climate of a very small or restricted area in contrast to the climate of the entire area, especially when this differs from the climate of the surrounding area, is a local atmospheric zone where the climate differs from the surrounding area

Explain how Earth’s curvature and axis of rotation influence the amount of sunlight reaching a given area, and how these factors influence the temperature and precipitation in that area.
Earths curved shape causes latitudinal variation in the intensity of sunlight. Sunlight strikes certain regions more directly causing more heat and light per unit of surface area to be delivered there (in thr tropics). In higher latitudes sunlight strikes Earth at an oblique angle and thus the light energy is more diffuse on Earth’s surface (this energy is solar radiation).
Because Earth is titled on its axis relative to its plane of orbit around the sun the intensity of solar radiation varies seasonally. The intense solar radiation near the equator initiates a global pattern of air circulation and precipitation.

rainshadow effect
When warm moist air approaches a mountain (air that flows upwards) the air rises and cools (at higher altitudes) and releases moisture on the windward side of the peak (releases water as rain and snow). On the leeward side of the mountain, cooler dry air descends (because less moisture is left in the air) absorbing moisture and producing a rain shadow. This rain shadow can determine/create where deserts are found (Wind goes up a mountain and the airmass cools and expands (because when it goes higher up there is less pressure; allowing the airmass to expand and the temp drops too). Temp decreases because the air expands. So now the air is cool and cool air cant hold much moisture so clouds start to form. It begins to rain and the windward side of the mountain is very wet. Now this airmass lost all of its moisture and is very dry so when it gets to the other side of the mountain/leeward side the airmass starts to sink. The airmass is sinking so the pressure is increasing and so now the temp of the air mass increases. So now there is a warm dry mass of air which creates a rain shadow which creates a dessert.)

A rain shadow is a patch of land that has been forced to become a desert because mountain ranges blocked all plant-growing, rainy weather. On one side of the mountain, wet weather systems drop rain and snow. On the other side of the mountain—the rain shadow side—all that precipitation is blocked.

living factors (Every environment on Earth is characterized by abiotic or nonliving factors and biotic or living factors)

nonliving factors (Every environment on Earth is characterized by abiotic or nonliving factors and biotic or living factors)

Biome is the major life zones characterized by vegetation type (in terresitoraL) or by the physical environment (in aquatic) and characterozed by the adaption of organisms to that particular enviroment

(Biomes are large areas on Earth with similar conditions, such as climates and living organisms)

What two abiotic factors shown here are most important in determining the distribution of the biome?
The two abiotic factors in the climograph that are the most important in determining the distribution of the biome is the annual mean temperature and the annual mean precipitation (climate is important to determine the distributioon of terristoral biomes; also pattern of climate like when it rains not just average rain)

Why is the Pacific Northwest so rainy? What causes the Mediterranean climate?
Ocean currents influence climate along the coasts of continents by heating or cooling overlying air masses across the land. Coastal regions are also generally wetter than inland areas at the same latitude (because the airmass is cooler so cant hold moisture). The Pacific northwest is so rainy because the cold California current that flows southward along northern America supports a coniferous rain forrest ecosystem along much of the continents pacific coast and large redwood groves farther south. The Mediterranean climate is caused by the gulf stream which carries warm water from the equator to the north atlantic.

What effect does elevation have on climate? Why do we say that hiking from Gatlinburg, Tennessee, at 393 meters of elevation in the Smoky Mountains region, to the top of Mount LeConte, at 2,010 meters, is like traveling to Canada?
Every 1,000 m increase in elevation produces an average temperature drop of 6 C. This is equivalent to that produced by an 880 km increase in latitude. This is one reason on why high elevation communities at a given latitude can be similar to communities at lower elevations much farther from the equator.
So the reason we can say that hiking from Gatlinburg, Tennessee, at 393 meters of elevation in the Smoky Mountains region, to the top of Mount LeConte, at 2,010 meters, is like traveling to Canada is because we are increasing in elevation and we are increasing in latitude from the equator so it is getting colder just like it is in Canada.

Give two examples of how global climate change can alter the current range of species.
1. fires can kill woody plants and keep a savanna from becoming the woodland that climate alone would support
2. hurricans and other storms create opening for new species in many tropical and temperate forsts.

tropical forest:
1. tropical rain forests rainfall is about: 200-400 cm annually. Tropical dry forests rainfall is about: 150-200 cm annually with a 6-7 month dry season.
2. Temperature is usally high averaging: 25-29 C.
3. Location/ Distribution: equalatorial and subequatorial regions.
4. Flora broadleaf evergreen tees are dominant in rain forests (while dry forest trees drop their leaves during the dry season)
5. Fauna: home to million of animal species (including 5-30 million still undescribed species of insects, spiders, and other arthropods). Animal diversity is higher than in any other terrestrial biome. The animals are adapted to the vertically layered environment and are often inconspicuous

1. rainfall: precipitation is low and highly variable generally less than 30 cm per year
2. temperature: varies seasonally and daily, it may exceed 50 C in hot deserts and fall below -30 C in cold deserts
3. Location/distribution: deserts occur in bands near 30 north and south latititude or at other latitudes in the interior of continents (for example the Gobi deser of north central asia)
4. Flora: dominated by low widely scattered vegetations; common plants include succulents such as cacti or euphorbs, deeply rooted shrubs, and herbs that grow during infrequent moist periods.
a. Desert plant adaptations include tolerance to heat and desiccation, water storage, reduced leaf surface area, and physical defenses such as spines and toxins in leaves.
b. Most desert plants carry out C4 or CAM photosynthesis
5. Fauna: scorpions, ants, beetles, snakes, lizards, migratory nd resident birds, and seed eating rodents
a. Many species in hot deserts are active at night when the air is cooler
b. Water conservation is a common adaptation and some animals can obtain all their water by breaking down carbohydrates in seeds

1. Rainfall: averages 30-50 cm per year and is seasonal with dry seaspn that can last up to 9 months
2. Temperature: averages 24-29 C but varies seasonally more than in tropical forests
3. Location/Distribution: equatorial and subequatorial regions
4. Flora: scattered trees oftern are throny and have small leaves (an apparent adaptation to the releativly dry condition), firs are common in the dry season and the dominat plant species are fire adapted and tolerant of seasonal drought, grasses and small nonwoody plants called forbs make up most of the ground cover
5. Fauna: large plant eating mammals such as; wildebeests and zebras, and predators including lions and hyenes. Domminet herbivores are insects especially terminates.

1. Rainfall: 30-50 cm and is highly seasonal with rainy winters and dry summers
2. Temperature: Fall winter and spring are cool with average temps of 10-12 C and average summer temperature is 30 C
3. Location/Distribution: midlatitude coastal regions on several continents
4. Flora: dominated by shrubs and smll trees adapted to frequent fires; some fires adapted shrubs produce seeds that will germinate only after a hot fire, food reserves stored in their roots enable them to resporut quickly and use nutrients released by the fire
a. Adaptations to drought include tough evergreen leaves which reduce water loss
5. Fauna: browsers such as deer and goats (that feed on twigs and buds of woody vegetations), also many insects, amphibians, small mammals, and birds

Temperate Grassland:
1. Rainfall: 30 to 100 cm and can be highly seasonal with dry winters and wet summers
2. Temperature: below -10 C in winter and reach 30 C in summer
3. Location/ Distribution: typically at midlatitudes often in the interior of continents
4. Flora: dominant plants are grasses and forbs (which vary in height from a few centimets to 2m in tall grass prairie), many graslnand plants have adaptations that help them survive periodic protracted droughts anf fire
5. Fauna: large mammals such as bison and wild horses (they help prevent establishment of woody shrubs and trees), burrowing ammals such as prairie dogs

Northern Confierous Forest/taiga:
1. Rainfall: 30 to 70 cm annually
2. Temperature: winters are cold, in siberia typically ranges from -50 C in winter to over 20 C in summer
3. Location/Distribution: in a broad band across northern north America and Eurasia to the edge of the artic tundra, is the largest terrestrial biome
4. Flora: Cone bearing trees (conifers): such as pine, spruce, fir, and helock (some species depend on fire to regenerate). The conical shape of many conifers prevents snow from accumulating and breaking their branches and their needle like or scale like leaves reduce water loss.
a. Plant diversity in the shrub and herb layers is lower than in temperate broadleaf forests
5. Fauna: migratory birds nest in northern coniferous forests, mammals including moose, brown bears, and Siberian tigers, periodic outbreak of insects (can kill vast tracts of trees).

Temperate Broadleaf Forest:
1. Rainfall: 70 to 200 cm annually (significant amounts fall during all seasons with winter snow in some forests)
2. Temperature: winter temperature averages around 0 C summers are humid with maximum near 35 C
3. Location/ Distribution: Midlatitiudes in the Nothern Hempishpere with smaller areas in Chile, South Africa, Australia, and New Zealand
4. Flora: dominant plant is deciduous trees (which drop their leaves before winter when low temperatures would reduce photosynthesis). In australia evergreen eucalyptus trees are common
5. Fauna: Nothern hempespere many mammals hibernate in winter while bird species migrate to ears with warmer climates

1. Rainfall: 20 to 60 ck annually in artic tundra but may exceed 100 cm in alpine tundra
2. Temperature: Winters are cold with average temperatures in some area below -30 C summer temperatures generally average less than 10 C
3. Location/ Distribution: covers expansive ares of the artic (amounting to 20% if the earth;s land surface). High winds and low temperatures produce alpine tundra on very high mountaintops at all latitiudes including the tropics
4. Flora: herbaceous; typically a mix of mosses, graases, and forbs, with some dwarf shrubs, trees, and lichens,
a. Permintaly frozen soil layer called permafrost restricts the growth of plant roots
5. Fauna: large grazing musk oxen are resident while caribou and reindeer are migratory, Preditors inckude bears, wolves, foxes, and snowy owls. Many bird species migrqate to the tundra for summer nesting

What is the largest marine biome, and how much of Earth’s surface does it cover?
The largest marine bio is the ocean. It covers 75% of the Earth’s surface.

the narrow top layer of an ocean or lake where light penetrates surface sufficiently for photosynthesis to occur (is where there is sufficient light for photosynthesis)(classified as light penetration)

the part of an ocean or lake beneath the photic zone where light does not penetrate sufficiently for photosynthesis to occurm(is where little light penetrates)(classified as light penetration)

the bottom surface of an aquatic environment (deep or sallow), consists of organic and inorganic sediments and is occupied by communities of organisms called the benthos (classified as open water or bottom)

the open water component of aquatic biomes (zone made up of photic and aphotic zone) (pysical and chemical properties of this zone vary greatly because of the vastness of this area, which extends from the uppermost waters down to the deeper layers near the benthic zone of a water column.) (open water or bottom) (any water in a sea or lake that is neither close to the bottom nor near the shore can be said to be in the pelagic zone. The word “pelagic” is derived from Greek πέλαγος (pélagos), meaning “open sea”. The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes from the surface of the sea almost to the bottom. Conditions differ deeper in the water column; the pressure increases, the temperature drops and less light penetrates. Depending on the depth, the water column, rather like the Earth’s atmosphere, can be divided into different layers)

Littoral zone
In a lake the shallow well lit waters close to shore (shallow well lit waters close to shore) (distance from shore and water depth)

limnetic zone
In a lake the well lit open surface waters far from shore (where water is too deep to support rooted aquatic plants)

are nutrient-poor and generally oxygen rich (a nutrient poor clear lake with few phytoplankton)

are nutrition rich and often depleted of oxygen in the deepest zone in summer and if covered with ice in winter. High rates of decomposition in deeper layer of eutrophic lakes cause periodic oxygen depletion (high rate of biological productivity supported by a high rate or nutrient cycling) (A eutrophic (“well-nourished”) lake has high nutrients and high plant growth. An oligotrophic lake has low nutrient concentrations and low plant growth)

are small drifting heterotrophs that graze on the phytoplankton

are surface-dwelling photosynthetic organisms (the collection of photosynthetic organisms that drift near the water’s surface)

shallow water above the continental shelf (relates to the shallow part of the sea near the coast)

is the part of the ocean 2,000-6,000 m below the surface

description: Is a standing body of water (from a few square meters to thousands of square kilometers), Light decreases with depth in a lake creating photic and aphotic zones. Typical autotrophs: phytoplankton including cyanobacteria. Typical heterotrophs: zooplankton/small drifting heterotrophs (graze on the phytoplankton). Human impact: Runoff from fertilized land and dumping of wastes lead to nutrient enrichment which can produce algal blooms, oxygen depletion, and fish kills

description:inundated by water (at least sometimes) and support plants adapted to water saturated soil. (develop in diverse habitatis including shallow basins, flooded banks of rivers and steams, and lake coasts.) Typical autotrophs:cattails and sedges. Typical heterotrophs: crustaceans, aquatic insect larvae, and muskrats (herbavoires). dragonflies, frogs, alligators, and herons (carnavoires). Human impact: draining and filling have destroyed up to 90% of wetlands

Streams and Rivers
Typical Autotrophs: phytoplankton or rooted aquatic plants. Typical Heterotrophs: diverse fishes and invertebrates. Human impact: municipal, agricultural, and industrial pollution degrade water quality and can kill aquatic organisms. dams impair the natural flow of streams and rivers and threaten migratory species such as salmon.

What role does dispersal play in the study of the distribution of species?
Dispersal is the movement of individuals or gametes away from their area of origin or from centers of high population density. The dispersal of organisms is critical to understanding the role of geographic isolation in evolution as well as the broad patterns of species distribution that wee see around the world today.
(Dispersion plays a role in the global distribution of organisms), It can be a key factor limiting the distribution of a species (like kangaroos could live anywhere else but cant go anywhere because they are land animals thus dispersion limits them)

list five examples of biotic factors that may influence species distribution.
1. Predators
2. Herbivores
3. Pollinators
4. Parasites
5. Pathogens

5 abiotic factors that influence living organisms
temperature, water and oxygen, salinity, sunlight, and rocks and soil

Temperature affects biological processes, Most organisms function best within a specific range of environmental temperature (For example cells may rupture if the water they contain freezes (at temp below 0 C) and proteins of most organisms denature at temperatures above 45 C)

Water and oxygen
Variation in water availability among habitats is import factor in species distribution, (For example species living at the seashore or in tidal wetlands can dry out when the tide recedes and terrestrial organisms face a nearly constant threat of drying. Another example is that many amphibians like frogs are particularly vulnerable to drying out because they use their most skin for gas exchange) Water effects oxygen availability in aquatic environments and in flooded soils; because oxygen diffuses slowly in water its concentration can be low thus limiting cellular respiration and other physical process (oxygen concnetrations is low in deep ocean and deep lake waters (because it diffuses slowly) and sediments where organic matter is abundant (because those organic matters require oxygen; he amount of organic matter in the water affects dissolved oxygen levels by lowering it. In general, the more organic matter you have in the water the lower the dissolved oxygen will be)

The salt concentration of water in the environment affects the water balance of organisms through osmosis. For example most aquatic organisms are restricted to either freshwater or saltwater (by their limited ability to osmoregulate), like clownfish can only live in saltwater.

Sunlight absorbed by photosynthetic organisms provides the energy that drives most ecosystems, Too little sunlight can limit the distribution of photosynthetic species, For example in aquatic environments most photosynthetic occurs near the surface (where sunlight is more available) so the photosynthetic species are restricted to the surface of the water.

Rocks and Soil
On land the pH, mineral composition, and physical structure of rocks and soil limit the distribution of plants and therefore of the animals that feed on them. For example the pH of soil can limit the distribution of organisms directly through extreme acidic or basic conditions or indirectly by affecting the solubility of nutrients and toxins. Another example in a rive the composition of the rocks and soil that make up the substrate (riverbed) can affect water chemistry which in turn influences resident organisms (in freshwater and marine environments the structure of the substrate determines the organisms that can attach to it or burrow into it)

What two pieces of data are needed to mathematically determine density?
Density is the number of individuals per unit area or volume.

What is the difference between density and dispersion?
Density of a population is the number of individuals per unit area or volume while dispersion is the pattern of spacing among individuals within the boundaries of the population

Explain the impact of immigration and emigration on population density. (To avoid confusion between these two terms, it might help to use this memory trick: immigration is the movement into a population, while emigration is the exiting of individuals from a population.)
Immigration and emigration alters and influence the density of many populations. (immigration and emigration alters population density, immigration is movement in to the population while emigration is movement exiting population so these two things alter how dense a population is)

is in which individuals are aggregated in patches.
– is the most common pattern of dispersion
– clumping is because the conditions is good there (like good resources, lots of food, good conditions)
– also clumping of animals may also be associated with mating behavior
– forming groups may also increase the effectiveness of predation or defense

(or evenly spaced) pattern of dispersion may result from direct interaction between individuals in the population
– Rarer than clumped patterns
– Uniform is because of Competition (society)
– Also uniform occurs in antagonistic social interaction such as territoriality (the defense of a bounded physical space against encroachment by other individuals

(unpredictable spacing) the position of individual in a population is independent of other individuals
– Random occurs in the absence of strong attraction or repulsion among individuals or where key physical or chemical factors are relatively constant across the study area

In what population statistics do demographers have a particular interest? How is this data often presented?
Birth rates and death rates are of particular interests to the demographers. This data is represented by making a life table. A life table is age specific summaries of the survival patter of a population

Is your biology class a cohort? Explain.
Yes because a cohort is a group of individuals of the same age and everyone except the teacher in my class will be around the same age.

What does a reproductive table show?
A reproductive table (or fertility schedule) is an age specific summary of the reproductive rates in a population. It is constructed by measuring the reproductive output of a cohort from birth until death.

factors that influence population density and dispersion patterns
ecological needs of species, structure of the environment, and interactions among individuals within the population (this also influences the characteristics of populations)

density to dispersion
because pop density (how many per area) differentiate it creates patterns of dispersion (how they move around from different areas)

is the study of the vital statistics of populations and how they change over time

survivorship curves
a plot of the proportion or numbers in a cohort still alive at each age, shows patterns of survival, classified three types: type 1, type 2, type 3

type 1
is a flat at the start (reflecting low death rates during early and middle life) and then drops steeply as death rates increase among older age groups. Many large mammals (including humans) that produce few offsprings but they take care of their offsprings exhibit this curve (taking care of their offsprings allows their offsprings for high rates of survival).

type 2
(is intermediate) with a constant death rate over the organisms life span. This curve is mostly found in rodents, invertebrates, lizards, and annual plants where they have a constant rate or mortality (is diagonal line)

type 3
drops sharply at the start (reflecting very high death rates for the young) but flattens out as death rates decline for those few individuals that survive the early period of die off. This curve is associated with organisms that produce very large numbers of offsprings but provide little or no care (like long lived plants, fishes, or most marine invertebrate) (example an oyster has millions of eggs and the larvae hatched from the eggs most die from predation or other causes, those few that survive long enough to catch a suitable substrate begin growing a hard shell tend to survive for a relatively long time)

What is the advantage to using per capita birth and death rates rather than just the raw numbers of births and deaths?
Using per capita birth and death rates the model is one which expresses the average number of births and deaths during a specific time interval (per capita is the average number of births and deaths per individual during the specified time interval: change pop size/change Time= B-D

Per capita birth rate
is the number of offsprings produced per time by an average member of the population (formula to calculate expected number of births per year in a pop of any size: Births= b (per capita rate) N (pop size)

Per capita death rate
Per capita death rate expected number of deaths per unit time in a population (used to estimate the pop size and data in life tables and reproductive tables) ( formula to calculate expected number of deaths per year in a pop of any size: D= m (per capita death rate) N (pop size)

What will the per capita birth and death rates be if a population is demonstrating zero population growth?
The per capita birth and death rates will be equal to each other when the population is demonstrating zero population growth. Births and deaths still occur in such a population but they balance each other out (2 are born 2 die)

per capita rate of increase
is the difference between per capita birth rate and death rate, it indicates whether a given population is growing (r>0) or declining (r<0) (r=b-m)

What does it mean for a population to be in exponential population growth?
Exponential population growth is when a population increases under ideal conditions (ex: members all of access to abundant food and free to reproduce at their physiological capacity). The per capita rate of increase under these conditions may assume the maximum rate for the species. (The size of a population that is growing exponentially increases at a constant rate, resulting
eventually in a J-shaped growth curve when population size is plotted over time)

In the graph below, explain why the line with the value of 1.0 shows a steeper slope that reaches exponential growth more quickly than does the line with the value of
The reason the 1.0 (red line) has a steeper slope than the 0.5 max rate (red line) is because the red line has a greater max rate than the blue line. A population with a higher maximum rate of increase will grow faster than one with a lower rate of increase because population growth depends on N (population) as well as rmax (maximum rate) (a larger population experience more births (and deaths) than small ones growing at the same per capita rate) (even though the rate if increase is constant the population grows more quickly when it is large than when it is small thus 1.0 gets progressively steeper over time)

What are two examples of conditions that might lead to exponential population growth in natural populations?
The j shaped curve of exponential growth is characteristic of some populations that are introduced into a new environment or whose numbers were drastically reduced and are rebounding.

(Elephants in south Africa grew exponentially because they were protected from hunting.
Another example is when a species has unlimited amount of food supply and resources.

One example is when a species has no predators/ are a protected species.
Another example is when a species)

What is carrying capacity?
Carrying capacity (K) is the maximum population size that a particular environment can sustain, it varies over space and time with the abundance of limiting rescources

What are six examples of limiting resources that can influence carrying capacity?
Energy, shelter, refuge from predators, nutrient availability, water, and suitable nesting sites are the limiting factors

in logestic model per capita rate of increase approaches zero
as the carrying capacity is reached

K selection
is selection for traits that are sensitive to population density and are favored at high densities. K selection is density dependent selection. K selection is said to operate in populations living at a density near the limit imposed by their resources (the carrying capacity K) where competition among individuals is stronger (needs offsprings to be smart and strong to out compete the competitors) (ex: mature trees growing in old growth forest)

R selection
is selection for traits that maximize reproductive success in uncrowded environments (low densities), density independent selection. R selection is said to maximize r (the per capita rate of increase) and occurs in environments in which population densities are well below carrying capacity or individuals face little competition (so doesn’t need much parental care to survive) (ex: weeds growing in abandoned agricultural field) (just to reproduce so something that makes lots of offsprings and reproduces quickly)

On what is the life history of an organism based?
The traits that affect an organism’s schedule of reproduction and survival make up it’s life history

What three variables form the life history of a species?
When reproduction begins (the age at first reproduction or age at maturity), how often the organisms reproduces, and how many offsprings are produced per reproductive episode

density-independent regulation
a birth or death rate that does not change with population density is, density independent. (similar to r-selection)

density-dependent regulation
a death rate that rises as population density rises, is density dependent. Also as is a birth rate that falls with risisng density. (similar to k-selection)

Explain the importance of immigration and emigration in metapopulations.
It helps ecologists understand population dynamics and gene flow in patchy habitats, providing a framework for conservation of species living in a network of habitat fragments and reserves.
A metapopulation is a group of populations linked by immigration and emigration