Ecology Chapter 9

In Damuth's study, population densities and body sizes spanned_______ orders of magnitude

5

what areas does a population inhabit?

A population of plants or animals might occupy a mountaintop, a river basin, a coastal marsh, or an island, all areas defined by natural boundaries. Just as often, the populations studied by biologists occupy artificially defined areas such as a country, county, or national park.

Evelyn Hutchinson

A single paper authored by G. Evelyn Hutchinson (1957) crystallized the niche concept. In this seminal paper titled simply "Concluding Remarks," Hutchinson defined the niche as an n-dimensional hypervolume, where n equals the number of environmental factors important to the survival and reproduction by a species. Hutchinson called this hypervolume, which specifies the values of the n environmental factors permitting a species to survive and reproduce, as the fundamental niche of the species. The fundamental niche defines the physical conditions under which a species might live, in the absence of interactions with other species. However, Hutchinson recognized that interactions such as competition may restrict the environments in which a species may live. He referred to these more restricted conditions as the realized niche, which is the actual niche of a species whose distribution is limited by biotic interactions such as competition, predation, disease, and parasitism.

Where does E. frutescens get enough water to evaporatively cool its leaves?

Although the distributions of E. frutescens and E. farinosa overlap a great deal on a geographic scale, these two species occupy distinctive microenvironments. As shown in figure 9.7, E. farinosa grows mainly on upland slopes, while E. frutescens is largely confined to ephemeral stream channels, or desert washes. Along washes, runoff infiltrates into the deep soils increasing the availability of soil moisture to E. frutescens.

self thinning

As the trees grow, density declines progressively until the mature trees live at low densities.

Robert Peters and Karen Wassenberg

Building on Damuth's analysis, Robert Peters and Karen Wassenberg (1983) explored the relationship between body size and average population density for a wider variety of animals. Their analysis included terrestrial invertebrates, aquatic invertebrates, mammals, birds, and poikilothermic vertebrates, representing a great range in size and population density.When Peters and Wassenberg plotted animal mass against average density, they, like Damuth, found that population density decreased with increased body size.

How did the tiger beetles get to the ranges that they live in now?

Ecologists suggest that during the last glacial period C. longilabris lived far south of its present range limits. Then with climatic warming and the retreat of the glaciers, the tiger beetles followed their preferred climate northward and up in elevation into the mountains of western North America. As a consequence, the beetles in the southern part of this species' range live in isolated mountaintop populations. This hypothesis is supported by the fossil records of many beetle species.

what is the distribution of the plants in the genus Encelia?

Encelia californica, the species with the least pubescent leaves, occupies a narrow coastal zone that extends from southern California to northern Baja California. Inland, E. californica is replaced by E. actoni, which has leaves that are slightly more pubescent. Still farther to the east, E. actoni is in turn replaced by E. frutescens and E. farinosa. These geographic limits to these species' distributions correspond to variations in temperature and precipitation.

hubbell and johnson observed workers from two different colonies arrive at the prospective nest site and fight for possession.

Fights may escalate into protracted battles. Hubbell and Johnson observed battles over a nest tree that lasted for 2 weeks. Each dawn, 15 to 30 workers from two rival colonies arrived at the contested nest site. The workers from the two rival colonies faced off in two swarms and displayed and fought with each other. In the displays, pairs of bees faced each other, slowly flew vertically to a height of about 3 m, and then grappled each other to the ground. When the two bees hit the ground, they separated, faced off, and performed another aerial display. Bees did not appear to be injured in these fights, which were apparently ritualized. The two swarms abandoned the battle at about 8 or 9 A.M. each day, only to re-form and begin again the next day just after dawn. While this contest over an unoccupied nest site produced no obvious mortality, fights over occupied nests sometimes killed over 1,000 bees in a single battle. These tropical bees space their colonies by engaging in pitched battles.

G. Caughley

G. Caughley and his colleagues (1987) found a close relationship between climate and the distributions of the three largest kangaroos in Australia. The eastern grey kangaroo, Macropus giganteus, is confined to the eastern third of the continent. This portion of Australia includes several biomes. Temperate forest grows in the southeast and tropical forests in the north. Mountains, with their varied climates, occupy the central part of the eastern grey kangaroo's range . The climatic factor that distinguishes these varied biomes is little seasonal variation in precipitation or dominance by summer precipitation. The western grey kangaroo, M. fuliginosus, lives mainly in the southern and western regions of Australia, which coincides largely with the distribution of the Mediterranean woodland and shrubland biome in Australia. The climatically distinctive feature of this biome is a predominance of winter rainfall. Meanwhile, the red kangaroo, M. rufus, wanders the arid and semiarid interior of Australia, areas dominated by savanna and desert. Of the three species of large kangaroos, the red kangaroo occupies the hottest and driest areas. Caughley and his colleagues explain that the northern areas are probably too hot for the eastern grey kangaroo, too wet for the red kangaroo, and too hot in summer and too dry in winter for the western grey kangaroo. However, they are also careful to point out that these limited distributions may not be determined by climate directly. Instead, they suggest that climate often influences species distributions through factors such as food production, water supply, and habitat. Climate also affects the incidence of parasites, pathogens, and competitors.

how did Grinnell's use of the term niche differ from Elton's use of the word?

Grinnell's ideas of the niche centered around the influences of the physical environment, while Elton's earliest concept included biological interactions as well as abiotic factors.

Hubbell and Johnson

Hubbell and Johnson observed that some species of stingless bees are highly aggressive to other members of their species from other colonies, while others are not. Aggressive species usually forage in groups and feed mainly on flowers that occur in high-density clumps. The nonaggressive species feed singly or in small groups and on more widely distributed flowers. Hubbell and Johnson studied several species of stingless bees to determine whether there is a relationship between aggressiveness and patterns of colony distribution. They predicted that the colonies of aggressive species would show regular distributions while those of nonaggressive species would show random or clumped distributions. They concentrated their studies on a 13 ha tract of tropical dry forest that contained numerous nests of nine species of stingless bees. They found that potential nest trees were distributed randomly through the study area and that the number of potential nest sites was much greater than the number of bee colonies. Hubbell and Johnson were able to map the nests of five of the nine species of stingless bees accurately. The nests of four of these species were distributed regularly. As they had predicted, all four species with regular nest distributions were highly aggressive to bees from other colonies of their own species. The fifth species, Trigona dorsalis, was not aggressive and its nests were randomly distributed over the study area. Figure 9.11 contrasts the random distribution of T. dorsalis with the regular distribution of one of the aggressive species, T. fulviventris.

what did the data show for the study conducted by Robert Peters and Karen Wassenberg?

If you look closely at the data in figure 9.20, however, it is clear that there are differences among the animal groups. First, aquatic invertebrates of a given body size tend to have higher population densities, usually one or two orders of magnitude higher, than terrestrial invertebrates of similar size. Second, mammals tend to have higher population densities than birds of similar size. Peters and Wassenberg suggest that it may be appropriate to analyze aquatic invertebrates and birds separately from the other groups of animals.

James H. Brown, David Mehlman, and George Stevens

James H. Brown, David Mehlman, and George Stevens (1995) analyzed large-scale patterns of abundance among birds across North America during the breeding season, the opposite season from that studied by Root. In their study these researchers used data from the Breeding Bird Survey, which consists of standardized counts by amateur ornithologists conducted each June at approximately 2,000 sites across the United States and Canada under the supervision of the Fish and Wildlife Services of the United States and Canada. For their analyses, they chose species of birds whose geographic ranges fall mainly or completely within the eastern and central regions of the United States, which are well covered by study sites of the Breeding Bird Survey. Like Root, Brown and his colleagues found that a relatively small proportion of study sites yielded most of the records of each bird species. That is, most individuals were concentrated in a fairly small number of hot spots. For instance, the densities of red-eyed vireos are low in most places (fig. 9.16). Clumped distributions were documented repeatedly. When the numbers of birds across their ranges were totaled, generally about 25% of the locations sampled supported over half of each population. Brown and his colleagues propose that these distributions are clumped because the environment varies and individuals aggregate in areas where the environment is favorable.

John Damuth

John Damuth (1981) produced one of the first clear demonstrations of the relationship between body size and population density. He focused his analysis on herbivorous mammals, ranging in size from small rodents, with a mass of about 10 g, to large herbivores such as rhinoceros, with a mass well over 106 g. As figure 9.19 shows, Damuth found that the population density of 307 species of herbivorous mammals decreases, from species to species, with increased body size.

passenger pigeons went extinct as a result of which one of Rabinowitz's risk factors?

Narrow Habitat tolerance

What role does resistance to drying play in the intertidal zonation of these two species (Chthamalus stellatus and Balanus balanoides)?

Of the two species, Balanus appears to be more vulnerable to desiccation. Higher rates of desiccation may exclude this species of barnacle from the upper intertidal zone.

Peters and Wassenberg expanded upon Damuth's research on density and body size by looking at which of the following in addition to herbivorous mammals? Poikilothermic vertebrates birds herbs invertebrates

Poikilothermic vertebrates birds invertebrates

reasons why ecologists study populations

Population studies hold the key to saving endangered species, controlling pest populations, and managing fish and game populations. They also offer clues to understanding and controlling disease epidemics. Finally, the greatest environmental challenge to biological diversity and the integrity of the entire biosphere is at its heart a population problem—the growth of the human population.

Donald Phillips and James MacMahon

Research by Donald Phillips and James MacMahon (1981) showed that the distribution of creosote bushes changes as they grow. They mapped and analyzed the distributions of creosote bushes and several other shrubs at nine sites in the Sonoran and Mojave Deserts. Because earlier researchers had suggested that creosote bush spacing changed with available moisture, they chose sites with different average precipitations. Precipitation at the study sites ranged from 80 to 220 mm, and average July temperature varied from 27° to 35°C. Phillips and MacMahon took care to pick sites with similar soils and with similar topography. They studied populations growing on sandy to sandy loam soils with less than 2% slope with no obvious surface runoff channels.

Terry Root

Root's analysis centers around a series of maps that show patterns of distribution and population density for 346 species of birds that winter in the United States and Canada. Although species as different as swans and sparrows are included, the maps show a consistent pattern. At the continental scale, bird populations show clumped distributions. Clumped patterns occur in species with widespread distributions, such as the American crow, Corvus brachyrhynchos, as well as in species with restricted distributions, such as the fish crow, C. ossifragus.

Results of Thomas Schultz, Michael Quinlan, and Neil Hadley's work

Schultz and his colleagues found that the metabolic rates of C. longilabris are higher and its preferred temperatures lower than those of most other ti ger beetle species that have been studied. These differences support the hypothesis that C. longilabris is adapted to the cool climates of boreal and montane forests. In addition, the researchers found that none of their measurements differed significantly among populations of C. longilabris. Figure 9.4 illustrates the remarkable similarity in preferred body temperature shown by foraging C. longilabris from populations separated by as much as 3,000 km and, perhaps, by 10,000 years of history. These results support the generalization that the physical environment limits the distributions of species. It also suggests that those limits may be stable for long periods of time.

attributes of rarity

Small geographic range, narrow habitat tolerance, and low population density. there are eight possible combinations of these factors, seven of which include at least one attribute of rarity.

sizes of areas inhabited by a population

The areas inhabited by populations range in size from the few cubic centimeters to millions of square kilometers.

E. californica

The coastal environments where E. californica lives are all relatively cool. However, average annual precipitation differs a great deal across the distribution of this species. Annual precipitation ranges from about 100 mm in the southern part of its distribution to well over 400 mm in the northern part.

While bacterial populations in soils or water can exceed 109 per cubic centimeter and phytoplankton densities often exceed 106 per cubic meter, populations of large mammals and birds can average considerably less than one individual per square kilometer. What factors produce this variation in population density?

The densities of a wide variety of organisms are highly correlated with body size. In general, densities of animal and plant populations decrease with increasing size. Population density declines with increasing organism size.

distribution

The distribution of a population includes the size, shape, and location of the area it occupies. A population also has a characteristic pattern of spacing of the individuals within it.

fish crow, C. ossifragus

The fish crow population, though much more restricted than that of the American crow, is also concentrated in a few areas (fig. 9.15b). Fish crows are restricted to areas of open water near the coast of the Gulf of Mexico and along the southern half of the Atlantic coast of the United States. Within this restricted range, however, most fish crows are concentrated in a few hot spots—one on the Mississippi Delta, another on Lake Seminole west of Tallahassee, Florida, and a third in the everglades of southern Florida. Like the more widely distributed American crow, the abundance of fish crows diminishes rapidly away from these centers of high density.

How does E. frutescens avoid overheating?

The leaves do not overheat because they transpire at a high rate and are evaporatively cooled as a consequence.

difference in the leaves of E. frutescens and E. farinosa.

The leaves of E. frutescens are nearly as free of pubescence as the coastal species, E. californica. However, E. frutescens grows side by side with E. farinosa in some of the hottest deserts in the world. Because they are sparsely pubescent, the leaves of E. frutescens absorb a great deal more radiant energy than the leaves of E. farinosa

environment of E. frutescens and E. farinosa

The rainfall in areas occupied by E. frutescens and E. farinosa is similar to the amount that falls in the areas occupied by E. actoni and E. californica. However, the environments of E. frutescens and E. farinosa are much hotter.

Donald Phillips and James MacMahon study results

The results of this study indicate that the distribution of desert shrubs changes from clumped to random to regular distribution patterns as they grow. The young shrubs tend to be clumped for three reasons: (1) because seeds germinate at a limited number of "safe sites," (2) because seeds are not dispersed far from the parent plant, or (3) because asexually produced offspring are necessarily close to the parent plant. Phillips and MacMahon proposed that as the plants grow, some individuals in the clumps die, which reduces the degree of clumping. Gradually, the distribution of shrubs becomes more and more random. However, competition among the remaining plants produces higher mortality among plants with nearby neighbors, which thins the stand of shrubs still further and eventually creates a regular distribution of shrubs. This hypothetical process is summarized in figure 9.13.

why is the relationship between size and density important?

The value of such an empirical relationship, whether for plants or animals, is that it provides a standard against which we can compare measured densities and gives an idea of expected population densities in nature.

what produces the three patterns of distribution?

These three basic patterns of distribution are produced by the kinds of interactions that take place between individuals within a population, by the structure of the physical environment, or by a combination of interactions and environmental structure. Individuals within a population may attract each other, repel each other, or ignore each other. Mutual attraction creates clumped, or aggregated, patterns of distribution. Regular patterns of distribution are produced when individuals avoid each other or claim exclusive use of a patch of landscape. Neutral responses contribute to random distributions.

Santa Catalina Mountains of southern Arizona

This mountain range rises out of the Sonoran Desert near Tucson, Arizona, like a green island in a tan desert sea. Vegetation typical of the Sonoran Desert, including the saguaro cactus and creosote bush, grows in the surrounding desert and on the lower slopes of the mountains. However, the summit of the mountains is topped by a mixed conifer forest. Forests also extend down the flanks of the Santa Catalinas in moist, shady canyons.

What excludes Chthamalus from the lower intertidal zone?

Though the larvae of this barnacle settle in the lower intertidal zone, the adults rarely survive there. It turns out that this species is excluded from the lower intertidal zone by competitive interactions with Balanus.

American Crow (Corvus brachyrhynchos)

Though the winter distribution of the American crow includes most of the continent, the bulk of individuals in this population are concentrated in a few areas. These areas of high density, or "hot spots," appear as red patches in figure 9.15a. For the American crow population, hot spots are concentrated along river valleys, especially the Cumberland, Mississippi, Arkansas, Snake, and Rio Grande. Away from these hot spots the winter abundance of American crows diminishes rapidly.

Phillips and MacMahon and other ecologists proposed that desert shrubs compete for water and nutrients, a competition that takes place belowground. How can we study these belowground interactions?

Work by Jacques Brisson and James Reynolds (1994) provides a quantitative picture of the belowground side of creosote bush distributions. These researchers carefully excavated and mapped the distributions of 32 creosote bushes in the Chihuahuan Desert. They proposed that if creosote bushes compete, their roots should grow in a way that reduces overlap with the roots of nearby individuals. The complex pattern of root distributions uncovered confirmed the researchers' hypothesis: Creosote bush roots grow in a pattern that reduces overlap between the roots of adjacent plants (fig. 9.14). Notice that the root systems of creosote bushes overlap much less than they would if they had circular distributions. Brisson and Reynolds concluded that competitive interactions with neighboring shrubs influence the distribution of creosote bush roots. Their work suggests that creosote bushes compete for belowground resources.

regular distribution

a distribution of individuals in a population in which individuals are uniformly spaced

population

a group of individuals of a single species inhabiting a specific area.

clumped distribution

a pattern of distribution in a population in which individuals have a much higher probability of being found in some areas than in others; in other words, individuals are aggregated rather than dispersed.

what was the earliest and most basic use of the word niche>

a recessed place in a wall where one could set or display items.

when studying the distribution patterns of bees, Hubbell and Johnson hypothesized that _______species would have regular patterns of nest distribution while______species would be clumped or random.

aggressive nonaggressive

what does large scale phenomena refer to?

areas over which there is substantial environmental change. In this sense, large scale may refer to patterns over an entire continent or patterns along a mountain slope, where environmental gradients are steep.

The tiger beetle C. longilabris is most frequently found in more northerly locations, however, in southern locations it is found ______.

at higher elevations

where does the tiger beetle, Cicindela longilabris, live?

at higher latitudes and higher elevations than just about any other species of tiger beetle in North America. In the north, C. longilabris is distributed from the Yukon Territory in northwestern Canada to the maritime provinces of eastern Canada. This northern band of beetle populations coincides with the distribution of northern temperate forest and boreal forest in North America. C. longilabris also lives as far south as Arizona and New Mexico. However, these southern populations are confined to high mountains, where C. longilabris is associated with montane coniferous forests.

_______ between individuals would produce a more clumped distribution

attraction

a proposed explanation for the distribution of creosote bushes is_______competition.

below ground competition

the difference between the realized and the fundamental niche is the additional requirement of ______factors as part of the definition of the ______ niche.

biotic realized

Brown et al. looked at bird distributions when they were in their _______ grounds.

breeding

how do organisms compensate for temporal and spatial variation in the environment?

by regulating body temperature and water content and by foraging in ways that maintain energy intake at relatively high levels. However, there are limits on how much organisms can compensate for environmental variation.

Pheromones

chemical substances secreted by some animals for communication with other members of their species. The pheromone secreted by these stingless bees attracts and aggregates members of their colony to the prospective nest site; however, it also attracts workers from other nests.

An environment with patchy distributions of nutrients, nesting sites, water, and so forth fosters _________distribution patterns.

clumped

Root found that over half of the bird population occurred in less than 25% of the site sampled. this would indicate that the birds had a _______ distribution.

clumped

animals living near watering holes would be an example of a ______distribution?

clumped

continuous environmental gradients can produce ________ species distributions based upon favorable environmental conditions occurring at specific location.

clumped

pheromones are chemicals used by organisms to ________other organisms

communicate with

__________ between creosote bushes was though to be the cause of their pattern of distribution

competition

in studying plant population densities, White found that densities ________ increasing body size.

decrease with

number of individuals per unit area

density

Joseph Connell

described how along the coast of Scotland, adult Chthamalus stellatus are restricted to the upper levels of the intertidal zone, while adult Balanus balanoides are limited to the middle and lower levels.

connell found that thee upper limits to the distributions of the intertidal barnacles are determined by susceptibility to ______.

dessication

Deborah Rabinowitz

devised a classification of commonness and rarity, based on combinations of three factors: (1) the geographic range of a species (extensive versus restricted), (2) habitat tolerance (broad versus narrow), and (3) local population size (large versus small).

characteristics that all populations share.

distribution density age distributions birth and death rates immigration and emigration rate of growth abundance

In nearly all cases, the key to a species' survival is increased _______ and _______.

distribution and abundance

there are limits to how much organisms can compensate for _______ variation.

environmental

patterns of distribution are driven by a combination of _____ and ____interactions

environmental and social

like peregrine falcons, tigers had ______ and _______ but low population density, resulting in an increased risk of extinction.

extensive geographic range broad habitat tolerance

peregrine falcons had ______ and ______ by low population density, resulting in an increased risk of extinction

extensive geographic range and broad habitat tolerances

Rabinowitz's rarity classification system is designed to evaluate whether a population is at risk for______.

extinction

the movement of tiger beetles northward and to higher elevations as a result of climatic warming is supported by evidence from ________.

fossil record

in a biodiversity survey of the great plains, you would expect to find______ numbers of field mice compared to bison in a defined sample area.

greater

the difference in pubescence between E. farinosa and E. frutenscens results in ______ by E. frutescens in order to prevent overheating.

greater transpiration

One of the environmental factors thought to affect thee relationship between range and population size is ________.

habitat tolerance

The most abundant species and those least threatened by extinction

have extensive geographic ranges, broad habitat tolerances, and large local populations at least somewhere within their range

in studying the relationship between population density and body size, Damuth analyzed data from ________.

herbivorous mammals

areas of high densities for a species are referred to as _______.

hot spots

precipitation may be _______influencing the distribution of kangaroos through other factors such as food production, habitat and even pathogens or parasites.

indirectly

random distribution

is one in which individuals within a population have an equal chance of living anywhere within an area

what are the environmental limits of a species related to?

its niche

In support of their hypothesis, Brisson and Reynolds found that the overlap of roots between adjacent plants was ____________ the expected overlap if the plants simply had a circular pattern of root growth

less than

Organisms living in a continental area can also be considered "island species when they ______.

live in extremely restricted locations

Research prior to Phillips and MacMahon indicated that creosote distribution was driven by ________.

moisture

Variation in leaf pubescence of Encelia species varied in relationship to _____along the gradient that Ehleringer and Clark studied.

moisture

whittaker and Neiring stidied plant distributions along_______ and _______ gradients in the mountains of arizona

moisture elevation

of the 154 bird species known to have become extinct since 1500, ______are species restricted to islands.

most

Mountain tops and river basins are considered to be ______boundaries, while countries and parks are considered to be ______ boundaries to populations.

natural artificial

what would happen to populations separated for many thousands of years that may have been exposed to significantly different environmental regimes.

natural selection could have produced significant physiological differences among populations

The environmental limits of a species is considered to be the specie's ________.

niche

E. actoni

occupies environments that are only slightly warmer but considerably drier than E. californica

large-scale phenomena

phenomena of a geographic scale rather than a local scale

small-scale phenomena

phenomena that take place on a local scale

what have populations evolved to compensate for environmental variation?

physiological, anatomical, and behavioral characteristics

James white

pointed out that plant ecologists have been studying the relationship between plant size and population density since early in the twentieth century. He suggests that the relationship between size and density is one of the most fundamental aspects of population biology. White summarized the relationship between size and density for a large number of plant species spanning a wide range of plant growth forms

the climatic factor that is most important is determining the distribution of large kangaroos in Austraila is _______.

precipitation

within their study area, Hubbell and Johnson found that potential nest trees were located in a ________ pattern.

random

. An environment with a fairly uniform distribution of resources and frequent, random patterns of disturbance (or mixing) tends to reinforce ______ or _______ distributions.

random or regular

Three basic patterns of distribution are observed on small scales:

random, regular, or clumped.

In response to competitive interactions, the spatial distribution of Chthamalus can be considered to be a _______ niche.

realized

habitat tolerance

related to the range of conditions in which a species can live. For instance, some plant species can tolerate a broad range of soil texture, pH, and organic matter content, whereas other plant species are confined to a single soil type. As we shall see, tigers have broad habitat tolerance; however, within the tiger's historical range in Asia lives the snow leopard, which is confined to a narrow range of conditions in the high mountains of the Tibetan Plateau

Island species are at extremely high risk for extinction due to which of Rabinowitz's risk factors?

restricted range narrow habitat tolerance small pop size

when swarms from different hives battled over potential nest sites, they engaged in________combat

ritualized

Thomas Schultz, Michael Quinlan, and Neil Hadley (1992)

set out to study the environmental physiology of widely separated populations of the tiger beetle, Cicindela longilabris. The researchers compared the physiological characteristics of beetles from populations of C. longilabris from Maine, Wisconsin, Colorado, and northern Arizona. Their measurements included water loss rates, metabolic rates, and body temperature preferences.

what does small scale phenomena refer to?

small distances over which there is little environmental change significant to the organism under study.

Peregrine falcons are at risk of extinction because of of which one of Rabinowitz's risk factors?

small pop size

on a mountain slope, where environmental change is steep, a "small-scale process" would be a _______lang area than an area where environmental change was more gradual

smaller

Robert Whittaker and William Niering

studied the distribution of plants along moisture and elevation gradients in the Santa Catalina Mountains of southern Arizona. There is a moisture gradient from the moist canyon bottoms up the dry southwest-facing slopes. Whittaker and Niering found that along this gradient the Mexican pinyon pine, Pinus cembroides, is at its peak abundance on the uppermost and driest part of the southwest-facing slope (fig. 9.17). Along the same slope, Arizona madrone, Arbutus arizonica, reaches its peak abundance at middle elevations. Finally, Douglas firs, Pseudotsuga menziesii, are restricted to the moist canyon bottom. Mexican pinyon pines, Arizona madrone, and Douglas fir are all clumped along this moisture gradient, but each reaches peak abundance at different positions on the slope. These positions appear to reflect the different environmental requirements of each species. Whittaker (1956) recorded similar tree distributions along moisture gradients in the Great Smoky Mountains of eastern North America. Again, the gradient was from a moist valley bottom to a drier southwest-facing slope. Along this moisture gradient, hemlock, Tsuga canadensis, was concentrated in the moist valley bottom and its density decreased rapidly upslope (fig. 9.18). Meanwhile, red maple, Acer rubrum, grew at highest densities in the middle section of the slope, while table mountain pine, Pinus pungens, was concentrated on the driest upper sections. As in the Santa Catalina Mountains of Arizona, these tree distributions in the Great Smoky Mountains reflect the moisture requirements of each tree species.

to an ecologist, niche summarizes the environmental characteristics that influence the ________, ________, and ________ of a species.

survival reproduction growth

By combining the results of Root and Brown and his colleagues, we can say confidently that ......

that at larger scales, bird populations in North America show clumped patterns of distribution. In other words, most individuals within a bird species live in a few hot spots, areas of unusually high population density.

realized niche

the actual niche of a species whose distribution is limited by biotic interactions such as competition, predation, disease, and parasitism.

who developed the concept of the niche?

the niche concept was developed independently by Joseph Grinnell (1917, 1924) and Charles Elton (1927), who used the term niche in slightly different ways.

to an ecologist, what does a niche summarize?

the niche summarizes the environmental factors that influence the growth, survival, and reproduction of a species. In other words, a species' niche consists of all the factors necessary for its existence—approximately when, where, and how a species makes its living.

density

the number of individuals per unit area

fundamental niche

the physical conditions under which a species might live, in the absence of interactions with other species

abundance

the total number of individuals, or biomass, of a species in a specified area.

what is the relationship between size of geographic range and population size.

there is a strong positive correlation between the two variables for most groups of organisms. In other words, species abundant in the places where they occur are generally widely distributed within a region, continent, or ocean, whereas species living at low population densities generally have small, restricted distributions.

True or False: In hutchinson's definition of niche, each environmental factor is an axis of an n-dimensional hypervolume.

true

true or false: from its name, you would expect fish crows to have hotspots near coastal locations

true

During the course of their growth, Phillips and McMahon found that the distribution pattern of creosote bushes ________ time.

varied with

through which of the following factors may climate be indirectly influencing the distributions of kangaroo species? (select all that apply) seasonality water supply food production habitat urban encroachment

water supply food production habitat

Schults found that measurements of water loss, metabolic rates and temperature preferences _______ between the populations of C. Longilabris.

were similar

which of the following would be areas where population biology would inform decision making? (select all that apply) wildlife management response to epidemics toxicology pest control

wildlife management response to epidemics pest control

one of the criticisms of Root's analysis of bird distributions was that it only looked at data from a time when the birds were on their _______ grounds.

wintering

Barnacles, one of the most common intertidal organisms, show distinctive patterns of_______ within the intertidal zone.

zonation