Biology 2 AP Ch. 46 LECTURE NOTES
Ecology is the scientific study of the interactions of organisms and their environments.
A complex and critical area of biology.
There are three key words in the definition: scientific, environment, and interactions.
I. Ecology is the scientific study of the interactions between organisms and their environments
The scientific nature of ecology involves using observations and experiments to test hypothetical explanations of ecological phenomena.
A multidisciplinary field examining questions from all areas of biology as well as many physical sciences.
The environment of an organism includes both biotic and abiotic factors.
Biotic factors include all other organisms that are a part of any individual organism's environment.
Abiotic factors are the temperature, light, water, nutrients, etc. to which an organism is exposed.
The interactions between organisms and their environments involve how the environment affects an organism and how an organism can change the environment.
Cyanobacteria began to use sunlight for photosynthesis about three billion years ago.
=> Oxygen, a by-product of photosynthesis, accumulated and resulted in an aerobic environment.
The shading of the forest floor by trees sometimes makes the floor unsuitable (due to reduced light) for their offspring to grow.
II. Basic ecology provides a scientific context for evaluating environmental issues
Although distinct, basic ecology and environmental issues have many connections.
To properly address environmental problems, it is necessary to understand the relationships between organisms and their environments.
Current environmental awareness began with Rachel Carson's Silent Spring which exposed the fact that widespread use of pesticides often affects nontarget organisms.
The realization that Earth is a finite resource and that pollution, overpopulation, and habitat destruction are threatening that resource is a concern of most people.
III. Ecological research ranges from the adaptations of organisms to the dynamics of ecosystems
A. The Questions of Ecology
Ecology can be divided into four comprehensive levels of inquiry:
Organismal ecology studies the behavioral, physiological, and morphological ways individuals meet abiotic environmental challenges.
=> The distribution of organisms is limited by their tolerance of abiotic conditions.
Population ecology studies groups of individuals of the same species in a particular geographic area.
=> Questions in population ecology concern factors that affect population size and composition.
Community ecology studies all organisms that inhabit a particular area.
=> Questions concern predation, competition and other interactions that affect community structure and organization.
Ecosystem ecology studies all abiotic factors as well as communities of organisms in an area.
=> Questions concern energy flow and chemical cycling among the abiotic and biotic components.
B. Ecology as an Experimental Science
Ecology has a long history as a descriptive science but is young as an experimental science.
Very difficult to conduct experiments and control variables.
Some test hypotheses in lab experiments and by manipulating populations and communities in field experiments.
Some devise mathematical models which include important variables and hypothetical relationships; usually studied with the aid of a computer.
C. Ecology and Evolution
Short term interactions of organisms with their environments could have long term effects through natural selection. Ecological time translates into effects over evolutionary time.
For example, predator-prey interactions may affect gene pools where individuals with protective coloration would become more prevalent.
The current distribution and abundance of organisms are products of long-term evolutionary changes and on going interactions.
IV. Climate and other abiotic factors are important determinants of the biosphere's distribution of organisms
The biosphere is that portion of Earth inhabited by life and represents the sum of all communities and ecosystems.
It is a thin layer consisting of seas, lakes, rivers, streams, the land to a soil depth of a few meters, and the atmosphere to an altitude of a few kilometers.
Biomes axe the major types of communities and ecosystems typical of broad geographic areas.
The different biomes form global patterns which reflect regional differences in climate and other abiotic factors.
Abiotic factors such as temperature, humidity, salinity, and light influence the distribution of organisms.
The patchiness of the global biosphere illustrates how different physical environments produce a mosaic of habitats.
A. Important Abiotic Factors
Some of the important abiotic factors that affect distribution of species include: temperature, water, sunlight, wind, rocks and soil, and periodic disturbances.
1. Environmental temperature affects biological processes and the ability of most organisms to regulate their body temperature.
Temperature greatly affects metabolism: few organisms have active metabolisms at temperatures close to 0°C, and temperatures above 45°C denature most essential enzymes.
The actual body temperature of ectotherms is affected by heat exchange with the environment.
=> Most animals maintain a body temperature only a few degrees above or below ambient temperature.
Even endotherms function best within the environmental temperature range to which they are adapted.
2. Water is essential and adaptations for water balance and conservation help determine a species' habitat range.
Marine and freshwater animals face the problems of regulating intracellular osmolarity; terrestrial animals face the problem of desiccation.
3. Sunlight provides the energy that drives nearly all ecosystems although only photosynthetic organisms use it directly as an energy source.
Light is not the most important limiting factor in terrestrial environments but may play a role as in the reduction of competition due to shading in a forest.
In aquatic environments, the distribution of photosynthetic organisms is limited by the intensity and quality of light.
=> Water selectively reflects and absorbs certain wavelengths; therefore, most photosynthesis occurs near the water surface.
The physiology, development, and behavior of many animals and plants are often sensitive to photoperiod.
4. Wind amplifies the effects of temperature by increasing heat loss by evaporation and convection.
Wind also increases the evaporation rate of animals and transpiration rate of plants, resulting in more rapid water loss.
Mechanical pressure of wind can effect plant morphology (for example, inhibiting growth of limbs on windward side of trees).
5. Rocks and soil. The physical structure, pH, and mineral composition of soil limit distribution of plants and hence animals that feed on those plants.
The composition of the substrate in a stream or river greatly influences the water chemistry, which in turn influences the plants and animals.
The type of substrate influences what animals can attach or burrow in intertidal zones.
6. Periodic disturbances such as fire, hurricanes, typhoons, and volcanic eruptions can devastate biological communities.
After which the area is re-colonized by organisms or repopulated by survivors.
=> May go through a succession of changes.
Those disturbances that are infrequent (volcanic eruptions) do not illicit adaptations. Adaptations do evolve to periodically recurring disturbances such as fires.
B. Climate and the Distribution of Organisms
Climate is the prevailing weather conditions at a locality.
The major components of climate are temperature, water, light, and wind.
Climate has a major impact on the distribution of organisms.
A climatograph plots temperature and rainfall in a particular region.
Usually in terms of annual means.
Must be careful to distinguish a correlation between climate variables and biomes from causation.
=> Only a detailed study of a species' tolerances to water and temperature ranges could establish the direct effects of these variables.
The fact that biomes overlap on climatographs indicate that factors other than mean temperature and rainfall play roles in determining biome location (i.e. soil composition).
C. Global Climate Patterns
Solar energy input and the Earth's movement in space determine the planet's global climate patterns.
About 50% of the solar energy that reaches the atmosphere's upper layers is absorbed before it reaches the surface.
Ultraviolet and certain other wavelengths are more readily absorbed by oxygen and ozone than other wavelengths.
Some of the solar energy that reaches the Earth's surface is reflected back into the atmosphere; large amounts are absorbed by land, water, and organisms.
The atmosphere, land, and water are heated when they absorb solar energy; this heating establishes the temperature variations, air movement cycles, and evaporation of water responsible for the latitudinal variations in climate.
Latitudinal variation in the intensity of sunlight results from the Earth's spherical shape;
seasonal variation in solar radiation in the Northern and Southern Hemispheres are due tc the Earth's tilt of 23.5° relative to its plane of orbit. (See Campbell, Figures 46.4 and 46.5)
Only the tropics (23.5°N to 23.5°S) receive sunlight from directly overhead yeai round; the tilt causes solar radiation to change daily as the Earth rotates around the sun.
The tropics receive the greatest annual input of solar radiation and show the leas1 seasonal variation; only small variations in daylength and temperature occur.
Seasonal variation in light and temperature increases steadily toward the poles; polai regions have long, cold winters with periods of continual darkness and shor) summers with periods of continual light.
A global circulation of air which creates precipitation and winds results from the intense solar radiation near the equator. (See Campbell, Figure 46.6)
Evaporation of surface water due to high tropical temperatures causes warm, wet ail masses to rise near the equator; this rising air creates an area of light, shifting winds (doldrums) along the equator.
As these warm air masses rise, they expand and cool; cool air can hold less watel vapor so the rising air masses drop large amounts of rain in the tropics.
The cool, dry air masses flow toward the poles at high altitudes; they continue tc cool as they move farther from the equator.
Air mass density increases as they become cooler; they begin to descend toward the( surface as cool, dry air masses at about 30° latitude.
The air masses absorb water as they descend, thus creating arid climates around 30°N and 30°S.
Some of the descending air masses flows toward the poles at low altitudes, the resi flows toward the equator.
The air masses flowing toward the poles are warmed and rise again at about 60°"N and 60°S; as these masses of air begin to cool with increased altitude, the watel vapor is lost as precipitation.
As air from this third cell reaches the higher altitude and cools, it flows toward the ( poles where it descends and flows back toward the equator).
The Earth's predictable wind patterns are established by air flowing in the circulation cells. The rotation of the Earth deflects the winds from a vertical path since land near the equator is moving faster than that at the poles.
Tropical and subtropical tradewinds blow from east to west.
In temperate zones, the predominating winds flow from west to east.
D. Local and Seasonal Effects on Climate
Although global climate patterns explain the geographic distribution of major biomes, local variations due to bodies of water and topographical features create a regional patchiness in climatic conditions.
The local variation in climate and soil have a major influence on less widely distributed communities and individual species.
Proximity of large bodies of water affect local climates.
Ocean currents are generated by the Earth's rotation and may heat or cool (depending on whether they are tropical or polar currents) air masses passing over them toward land; evaporation is also greater over the ocean than over land.
Coastal areas are moister than inland areas at the same latitude; the California current flows from North to South along the west coast and helps form the cool, moist climate in this area.
During warm summer days, air over land heats faster than that over the ocean or large inland lakes; this warmer air rises, drawing a cool breeze from the water across the land.
Topographical variations, such as mountains, also exert an influence on solar radiation, local temperature and rainfall.
In the Northern Hemisphere, south-facing slopes receive more sunlight and are therefore warmer and drier than north-facing slopes.
=> The vegetation differs with south-facing slopes being covered by shrubby, drought resistant plants while the north-facing slopes have forests.
Air temperature declines 6° C for each 1000m increase in elevation.
=> This parallels the decline in temperature associated with increasing latitude.
=> For this reason, mountain communities are similar to those at lower elevations farther from the equator.
Deserts commonly occur on leeward sides of mountains.
=> This results from the movement of air masses over the mountain which produces a rainshadow.
=> When warm, moist air moves over a mountain, its altitude is increased and it cools; cooling causes the air to release its moisture as rain on the windward side.
=> The cooler, drier air then flows down the leeward side of the mountain; the cool dry air is warmed and absorbs moisture, producing the rainshadow.
The Earth's orbit around the sun causes seasonal changes in local conditions.
The changing angle of the sun causes slight shifts in the wet and dry air masses on either side of the equator.
=> These shifts result in the wet and dry seasons at 20° latitude where tropical deciduous forests grow.
Seasonal changes in wind patterns produce variations in ocean currents, sometimes causing upwellings that bring nutrient rich water from the deep ocean layer to the surface.
Seasonal temperature changes also cause the temperature profiles that develop during the summer in temperate zone ponds and lakes.
=> These profiles reverse in the autumn and spring resulting in biannual mixing that brings nutrient-rich water from the bottom to the top. (See Campbell, Figure 46.8)
Climate also varies on a smaller scale, the microclimate. Microclimate refers to small areas within a habitat that may have very different conditions than the overall area (e.g. under a rock, a forest floor).
Cleared areas in a forest generally show greater temperature extremes than the shaded forest floor due to greater solar radiation and wind currents.
Low lying areas are usually moister than high ground and support different forms of vegetation.
The area under a large stone or log is protected from extremes of temperature and moisture; a large number of small organisms usually live in such sheltered areas.
V. The costs and benefits of homeostasis affect an organism's responses to environmental variation
Organisms live in an integrated environment which includes various combinations of abiotic factors. The success of an organism reflects overall tolerance to the complete set of variables it encounters.
Some polar organisms tolerate air temperatures of -70°C, while desert organisms survive at 45°C or higher.
Aquatic organisms are found in waters with near zero salinity, while some tolerate salinities several times that of sea water.
No organism can survive the full range of environmental conditions present on Earth; each population or species is distributed, at least in part, based on its tolerance for a specific subset of environmental conditions.
Various anatomical structures and physiological mechanisms have evolved as adaptations to environmental constraints.
Organisms survive and reproduce in areas where environmental conditions to which they are adapted are found.
The ability to tolerate one factor may be dependent on another factor; for example, many aquatic ectotherms can tolerate reduced oxygen at low temperatures, but not at high temperatures which cause higher metabolic rates.
A. Regulators and Conformers
Organisms faced with a fluctuation in an environmental variable may maintain the homeostasis of their bodies through behavioral and physiological mechanisms (regulators) or by allowing their internal conditions to vary with external conditions (conformers).
Some species are conformers under certain conditions and become regulators under others.
Energy expenditure by the animal is necessary if behavioral or physiological mechanisms are used to maintain homeostasis.
For organisms to survive and reproduce, the energy "cost" of regulation cannot exceed the benefits of homeostasis.
Since few organisms are perfect regulators or perfect conformers, a majority of organisms represent a group of evolved strategies which permits them to live in their specific environment.
B. The Principle of Allocation
The Principle of Allocation is an important concept for assessing the responses of organisms to a complex environment.
This principle holds that each organism has a limited amount of energy that can be allocated for obtaining nutrients, escaping predators, coping with environmental fluctuations, growth, and reproduction.
Energy expended for one function reduces |the amount of energy available for other functions.
If an organism expends a large amount of energy to maintain homeostasis, less is available for growth, reproduction, and other functions.
The distribution of organisms and the homeostatic mechanisms they possess establish different priorities for energy allocation.
Conformers living in a stable environment may have more energy available for growth and reproduction; however, their geographic distribution is restricted due to intolerance to environmental change.
Regulators that allocate a large amount of energy to survive environmental changes have less available for other functions so they grow and reproduce less efficiently; however, they can survive and reproduce over a wider range because they can cope with changing environmental conditions.
VI. The response mechanisms of organisms are related to environmental grain and the time scale of environmental variation
Since environments vary over space and time, the impact of the variations on a particular species depends on the scale of the variation in relation to the species' overall life history.
A. Environmental Grain
The concept of environmental grain is used by ecologists to define an organism's use oi spatial variation in the environment.
A coarse-grained environment is one in which environmental patches are so large in relation to the size and activity of the organism that an individual organism can choose among patches.
A fine-grained environment is one in which environmental patches are small relative to the size and activities of an organism, and the organism may not behave as though patches exist.
An environment may be course-grained to one organism and fine-grained to another.
=> A field of wild flowers is coarse-grained for small herbivorous insects since some plants may be preferential reproductive sites or food sources.
=> The same field would be fine-grained to a large herbivorous mammal that feeds indiscriminately on all the plants.
Temporal variation in an environment may also be coarse-grained or fine-grained depending on the periodicity of the variation relative to the organism's lifespan.
Daily environmental variations are usually fine-grained for most organisms.
Seasonal and long-term shifts in climate are usually coarse-grained to all organisms.
Organisms exhibit a variety of adaptations as responses to spatial and temporal variations in the environments. Some of these adaptations have short activation times while others take much longer.
Behavioral adaptations are instantaneous and easily reversed.
Physiological adaptations are activated and reversed on a time scale from seconds to weeks, depending on the specific response.
Morphological adaptations may occur during an individual's lifespan or over generations.
Adaptive genetic changes in populations take several generations to appear.
The appropriate response to environmental change depends to a large degree on the duration of the change.
B. Behavioral Responses
Behavioral responses to unfavorable environmental changes include an animal's movement to a new, more favorable location and modification of the immediate environment by cooperative social behavior. For example,
Fish descend into deeper, cooler waters of a lake during summer when the upper layer becomes too warm.
Desert animals return to burrows or move into the shade during the day when heat is most intense.
Migratory birds migrate to warmer climates to overwinter.
Honeybees seal the hive during cold periods to conserve heat and cool the hive on hot days by the collective beating of their wings.
Small mammals may huddle in burrows in cold weather which minimizes the total surface area exposed to cold air, thus reducing heat loss.
C. Physiological Responses
Physiological responses to environmental change are generally slower than behavioral responses although some may occur very rapidly.
A slow change occurs when a human moves to an area of less oxygen such as at higher altitudes.
=> After several days to a few weeks the person responds with an increased number of red blood cells being produced.
An example of a faster change would be when blood vessels in the skin constrict within seconds to reduce loss of body heat when the skin is exposed to very cold air.
Physiological adaptation is centered around regulation and homeostasis.
Both regulators and conformers function most efficiently under certain environmental conditions which are optimal for the organism.
Efficiency declines both above and below optimal values.
Physiological responses to changing environments can shift tolerance limits of organisms (acclimation).
Acclimation is a gradual process and is related to the range of environmental conditions experienced under natural conditions.
D. Morphological Responses
Organisms can react to environmental change with responses that alter body form or internal anatomy.
May be forms of acclimation since they are reversible.
=> Increase in coat fur or feather density in winter. => Change in coat color between winter and summer.
Other morphological changes are irreversible over an individuals lifespan since the environmental variation may have affected growth and differentiation patterns.
=> Plants are more morphologically plastic than animals.
=> The arrowleaf plant lacks a waxy leaf cuticle when growing in water with submerged leaves (allows absorption of materials directly from the water).
π Arrowleaf plants growing on land have a thick cuticle (reduces water loss) and an extensive root system.
E. Adaptation over Evolutionary Time
It is important to remember that behavioral, physiological, and morphological responses to environmental change have evolved over evolutionary time to their current levels through natural selection.
What appear to be short-term adjustments are actually evolutionary adaptations to maintain homeostasis.
Natural selection also places constraints on the distribution of populations by adapting them to localized environments.
Organisms adapted to one type of environment may not survive if dispersed to a foreign environment or may become extinct if the local environment changes to beyond their tolerance limits.
The existence of a species in a particular location depends on the species reaching that location and being able to survive and reproduce after getting there.
VII. The geographical distribution of terrestrial biomes is based mainly on regional variations in climate
Biomes are communities and ecosystems typical of broad geographic regions.
Ecologists recognize and organize biomes in different ways since there are no strict guidelines for defining biomes.
Distributional patterns of organisms within the biosphere are the major focus of ecological research.
The climate and other abiotic factors are important in determining why a particular biome is found in an area.
There are latitudinal patterns of biome distribution over the Earth's surface due to the latitudinal patterns in climate.
Terrestrial biomes are often named for the predominant vegetation, but each is also characterized by microorganisms, fungi, and animals adapted to that particular environment.
Biomes grade into each other without sharp boundaries and may form ecotones, transitional areas between two communities.
Species composition may vary from one location to another within a biome.
May be patchy, with several communities represented in one biome.
π Usually recognized on the basis of communities that develop through succession.
Tropical forest is found near the equator (within 23.5° latitude) where temperatures vary little from about 23°C and the length of daylight varies only slightly from 12 hours.
Rainfall is variable and the amount determines what vegetation is found in an area.
In lowlands with prolonged dry seasons and scarce rain, tropical dry forests occur; these are a mixture of thorny trees and shrubs, and succulents.
In regions with distinct wet and dry seasons, tropical deciduous forests occur. Trees re-leaf following heavy rains and drop leaves during the dry season.
Near the equator where rainfall is abundant (> 250 cm/year) and the dry season lasts less than a few months is tropical rain forest. (See Campbell, Figure 46.13)
Has the greatest diversity, harboring more plant and animal species than any other biome.
The vegetation is divided into five general layers: trees emerging above the canopy;the canopy which is the topmost continuous layer of foliage; the low tree stratum;
the shrub understory; and the ground layer of herbaceous plants and ferns.
A horizontal mosaic of changing vegetation is also present.
The great plant diversity supports a great animal diversity.
Widespread individuals of plant species depend on animals for pollination and dispersal of fruits and seeds.
Competition for light is a strong selective force in plant communities.
Soils are typically poor due to rapid nutrient recycling.
Destruction of tropical rain forests, occurring rapidly due to human intervention, may cause large-scale changes in world climate as well as destruction of many species.
B. Savanna
Savanna is grassland with scattered individual trees. (See Campbell, Figure 46.14)
Cover areas of central South America, central and southern Africa, and parts of Australia.
The three distinct seasons occur in sequence: cool-dry; hot-dry; warm-wet.
Soils are generally: poor in nutrients; porous with a thin humus layer; have rapid water drainage.
Usually have a simple physical structure but are often rich in species numbers.
Frequent fires inhibit invasion by trees to maintain the grasses (wind pollinated) and forbs (often insect pollinated).
The dominant herbivores are insects (ants, termites) although they are less obvious than other animals.
Large herbivores (zebras, giraffes, kangaroos) and burrowing animals are commonly most active in the rainy season and many are nocturnal.
=> During the dry season, many small animals are dormant or survive on seeds and dead plant parts while large animals migrate.
Savannas are examples ofecotones, where forest and grassland biomes integrate.
The climatic conditions and community features are intermediate between grassland and forest.
Human impact on savannas has existed for centuries although the modem impact has been severe and detrimental.
Population pressure, intensified grazing, and firewood collection have destroyed much of the vegetation in the Sahel region of Africa.
Loss of vegetation has reduced water vapor recirculation to the atmosphere which has devastating climatic consequences for the region.
C. Desert
Desert is characterized by low and unpredictable precipitation (< 30 cm/year), not by temperature: both cold and hot deserts exist.
Occur in two distinct belts on Earth: between 15° and 35° latitude in both hemispheres.
=> A result of global air circulation with the descending air absorbing the available moisture.
Hot deserts occur in S.W. United States, W. South America, North Africa, the Middle East, and Central Australia.
Cold deserts occur in E. Argentina, central Asia and west of the Rocky Mountains.
The density of vegetation cycles, with the growth and reproductive cycles being keyed to precipitation.
No perennial vegetation is found in the driest deserts due to a lack of rainfall which is usually <2 cm/year.
Dominant vegetation in less arid deserts includes scattered shrubs, cacti and other succulents that store water.
=> Many bloom abundantly after a rainfall.
Reptiles and seed eaters such as ants, birds and rodents are common. Many live in burrows, are nocturnal or have other adaptations for conserving water.
Light coloration reflects sunlight.
Some mice never drink and derive all of their water from the metabolic breakdown of the seeds they eat.
The reproductive cycle of some (i.e. spadefoot toads) is completed quickly in temporary pools.
D. Chaparral
Chaparrals are regions of dense, spiny shrubs with tough evergreen leaves. They are found along coasts where cool ocean currents circulate offshore resulting in mild, rainy winters and long, hot, dry summers.
Are found between 30° and 40° latitude.
Occur in Mediterranean and coastlines of California, Chile, S.W. Africa, and S.W, Australia.
Shrubby vegetation dominates since: low nutrient soils, aridity, short growing seasons, and frequent fires prevent trees from becoming established.
Vegetation from these areas are similar in appearance but taxonomically unrelated.
Chaparral is maintained by periodic fires.
Many shrubs have root systems and seeds adapted for fire; root crowns may be fire resistant and resprout quickly, others have seeds that only germinate after a fire.
Other plants are clonal and use asexual reproduction.
Browsers such as deer, fruit-eating
birds, seed-eating ants and rodents, snakes and lizards are common animals of
these biomes.
E. Temperate Grasslands
Temperate grasslands have some characteristics of tropical savannas but occur in regions with relatively cold winters.
The veldts of southern Africa, the pampas of Uruguay and Argentina, the steppes of the former Soviet Union and the plains and prairies of the U.S. are examples.
Occasional fires and seasonal drought prevent encroachment of trees into grasslands.
Soil tends to be deep and rich with a large amount of decaying plant matter (mulch) being deposited each year.
=> Mulch decreases runoff and erosion, stabilizes soil temperature, and improves conditions for seed germination.
=> Too much mulch may suppress grass growth and allow invasion by wood plants.
Grazing and burning reduce mulch accumulation.
Large grazing mammals and large carnivores are common, and burrowing rodents and other small mammals are present in dense populations.
Underground invertebrates graze on the below-ground parts of the plants.
Few natural grasslands remain due to their conversion to farm and pasture lands.
F. Temperate Deciduous Forest
Temperate forests grow throughout midlatitude regions with sufficient moisture to support growth of large, broad-leaved deciduous trees.
Occur in Eastern U.S., Middle Europe and E. Asia.
Temperatures range from very cold in winter to very hot in summer (-30°C to 30°C), with a 5 to 6 month growing season.
Precipitation is fairly high and evenly distributed throughout the year.
Soil is rich in nutrients; decomposition rates are slow and a thick layer of leaf litter usually accumulates.
Several layers of vegetation including herbs, shrubs and one or two strata of trees (species composition varies widely) are present.
Dominant trees are usually oak, birch, hickory, beech, and maple species.
Plant diversity is high and results from high availability of light, nutrients, and moisture.
Variety and abundance of food and habitat supports a rich diversity of animal life.
Logging, clearing, and the introduction of exotic pests and diseases have greatly reduced the amount of these forests.
G. Taiga
Taiga (coniferous or boreal forest) is characterized by harsh winters and short, wet (and occasionally warm) summers.
This is the largest terrestrial biome and occurs in North America, Europe, Asia and at high elevations in more temperate latitudes.
There is considerable precipitation, mostly in the form of snow that insulates the soil and prevents the permafrost; also provides a protective layer for small mammals.
Conifers like spruce, pine, fir or hemlock and deciduous oak, birch, willow, alder and aspen are common; usually one or very few species are present in dense stands.
=> Very little undergrowth is present.
Animals include: seed eaters such as squirrels, birds, and insects; browsers such as insects, elk, moose, deer, beaver, and porcupine; predators such as grizzly bears, wolves, wolverines and lynxes.
Soil is thin, acidic and forms slowly due to low temperatures and slow decomposition of waxy needles.
Coastal coniferous forests are similar to taiga in that they are dominated by one or a few species.
These are the temperate rain forests and redwood forests of the Pacific Northwest.
Their proximity to the ocean makes them much warmer and moister than the taiga.
H. Tundra
Tundra is at the northern-most limits of plant growth and plant forms are limited to low shrubby or matlike vegetation. (See Campbell, Figure 46.20)
There are two types of tundra:
Arctic tundra encircles the North Pole and extends southward to the taiga.
=> The climate is very cold with little light for long periods. Some areas are characterized by permafrost (permanently frozen ground) which contributes to the absence of taller plant forms.
=> Little precipitation may occur although permafrost, low temperatures, and low evaporation results in continually saturated soils - further restricting plant forms.
π Dwarf perennial shrubs, sedges, grasses, mosses and lichens are common.
=> Plant growth and reproduction occur rapidly during the brief warm summer.
Alpine tundra occurs at high elevations in all latitudes at altitudes above where trees can grow.
=> Near the equator, alpine tundra is confined to the highest mountain tops where freezing temperatures occur nightly.
=> The flora and fauna are similar to that of the arctic tundra.
Both arctic and alpine tundras have a low diversity of animal species.
Dipterans (blackflies, mosquitoes) are abundant in the arctic tundra's summer but scarce in the alpine tundra where beetles, grasshoppers, and butterflies are common.
Insect development is slower in the tundra due to the environmental conditions.
A large diversity of migratory birds enter the arctic tundra during the summer to feed on insects; herbivorous birds are rare.
π Large herbivorous mammals (muskox, caribou, reindeer) are common in the arctic tundra, as well as many small herbivores (lemmings).
Predators include the arctic fox, wolves, polar bears, and snowy owl.
VIII. Aquatic ecosystems, consisting of freshwater and marine biomes, occupy the largest part of the biosphere
Life arose in water and evolved there for almost three billion years before moving into terrestrial habitats.
Aquatic habitats still occupy the largest part of the biosphere.
Freshwater and marine biomes are distinguished on the basis of physical and chemical differences that influence the communities occupying these habitats.
Freshwater biomes have a salt concentration less than 1%; marine biomes average 3% salt concentration.
Freshwater biomes are closely linked to the terrestrial biomes where they are located or through which they flow.
Runoff from terrestrial habitats creates streams and rivers.
Accumulated runoff creates ponds and lakes.
Also influenced by the patterns and speed of water flow, and the climate to which they are exposed.
The oceans cover 75% of Earth's surface and contain the marine biomes.
Evaporation from the oceans provides most of the rainfall.
Ocean temperatures greatly effect world climate and wind patterns.
Marine algae consume a large amount of the atmospheric carbon dioxide and produce a major portion of the world's oxygen.
A. Ponds and Lakes
These standing bodies of water vary greatly in size w\t\\ ponds being smaller than lakes.
Ponds and lakes usually exhibit a significant vertical stratification in light penetration and water temperature.
There is a decrease in light intensity with increasing depth as light is absorbed by the water and suspended microorganisms. This divides the pond or lake into two layers:
=> The photic zone is the upper layer where light is sufficient for photosynthesis. => The lower aphotic zone receives little light and no photosynthesis occurs.
Temperature stratification also occurs in deeper ponds and lakes during summer in temperate zones.
=> Heat energy from sunlight warms the upper layers of water as far as it penetrates; the deeper waters remain cold.
As depth increases, the separation point of the wanner upper water form the lower colder water is noticeable as the thermocline.
π The thermocline is a narrow vertical zone between the warmer and colder waters where a rapid temperature change occurs.
The distribution of plants and animals within a pond or lake also shows a stratification based on water depth and distance from the shore.
The littoral zone is shallow, well-lighted, warm water close to shore.
=> Characterized by the presence of rooted and floating vegetation, and a diverse attached algal community (especially diatoms).
=> There is a diverse animal fauna including suspension feeders (clams);
herbivorous grazers (snails); and herbivorous and carnivorous insects, crustaceans, fishes, and amphibians.
=> Some reptiles, water fowl, and mammals also frequent this zone.
The limnetic zone is the open, well-lighted waters away from shore.
=> Occupants include photosynthetic phytoplankton (algae and cyanobacteria), zooplankton (rotifers and small crustaceans) that graze on phytoplankton, and small fish which feed on the zooplankton.
π Occasional visitors to this zone are large fish, turtles, snakes, and piscivorous birds.
The profundal zone is the deep, aphotic zone lying beneath the limnetic zone.
=> This is an area of decomposition where detritus (dead organic matter that drifts in from above) is broken down.
=> Water temperature is usually cold and oxygen is low due to cellular respiration of decomposers.
=> Mineral nutrients are usually plentiful due to decomposition of detritus.
Waters of the profundal zone usually do not mix with surface waters due to density differences related to temperature.
Mixing of these layers usually occurs twice each year in temperate lakes and ponds;
thus, oxygen enters the profundal zone and nutrients are cycled into the limnetic zone.
Lakes are often classified as oligotrophic or eutrophic, depending on the amount of organic matter produced.
Oligotrophic lakes are deep, nutrient-poor lakes in which the phytoplankton is not very productive.
=> The water is usually clear and the profundal zone has a high oxygen concentration since little detritus is produced in the limnetic zone to be decomposed.
Eutrophic lakes are usually shallow, nutrient-rich lakes with very productive phytoplankton.
=> The waters are usually murky due to large phytoplankton populations and the large amounts of detritus being decomposed may result in oxygen depletion in the profundal zone during the summer.
Oligotrophic lakes may develop into eutrophic lakes over time.
Runoff
from surrounding terrestrial habitats brings in mineral nutrients and sediments.
Human activities increase the nutrient content of runoff due to lawn and agricultural fertilizers; municipal wastes dumped into lakes dramatically enriches the nitrogen and phosphorus concentrations which increases phytoplankton and plant growth.
Algal blooms and increased plant growth results in more detritus and can lead to oxygen depletion due to increased decomposition.
=> This cultural eutrophieation usually makes the water unusable.
B. Streams and Rivers
Streams and rivers are bodies of water that move continuously in one direction.
There is a change in structure of these bodies of water from their headwaters (point of origin) to their mouths (where they empty into a larger body of water).
At the headwaters, the water is cold and clear, carries little sediment, and has few mineral nutrients.
=> The channel is narrow with a rocky substrate and the water flows swiftly.
Near the mouth, water moves slowly and is more turbid due to sediment entering from other streams and erosion; the nutrient content is also higher.
=> The channel is usually wider with a silty substrate that has resulted from deposition of silt.
The nutrient and oxygen content, turbidity, and rate of flow in rivers and streams are influenced by many factors.
Rough, shallow bottoms produce rapid turbulent flow known as riffles; smooth, deep bottoms result in a slower, smooth flow in areas called pools.
Nutrient content of the water is higher in streams and rivers flowing through densely vegetated regions and where erosion takes place.
π Leaves and other vegetation entering the water add organic matter.
π Erosion of rocks in the streambed increases inorganic nutrient content.
Oxygen content of the water is also affected by the flow rate.
=> Turbulent flow constantly oxygenates the water while slow, murky waters contain relatively little oxygen.
Turbidity reflects the amount of material suspended in the water.
=> Streams and rivers flowing through areas of high erosion will have more suspended materials than those surrounded by hard substrates.
=> Large amounts of suspended organic matter also increases turbidity.
The biological communities found in rivers and streams differ from headwaters to mouth;
they also differ from those found in ponds and lakes.
Due to the current, large plankton communities are not found in rivers and streams.
=> Photosynthesis which supports the food chains is carried out by attached algae and rooted plants.
Organic material washed into the system also provides an important food source, especially where dense vegetation along the shore blocks out sunlight or high turbidity in slow waters prevents light penetration.
In upstream areas where water is cool, clear, and has a high oxygen content, there are many aquatic insects and fish such as trout.
Near the mouth where water is murky and warmer with a lower oxygen content, fish such as carp and catfish are prominent; a different group of insects is also found in this area.
Various adaptations are found in organisms which permit them to inhabit their specific areas of rivers and streams.
Small animals typically have flattened bodies and can attach temporarily to rocks.
Many insects and other invertebrates live on the underside or downstream sides of rocks to escape the current.
Some insects produce silken nets used to filter food from the water.
Human activities have greatly affected many streams and rivers.
Channelization (increases flow rate) and damming (slows flow rate) alter the natural characteristics of flowing waters.
Pollutants may be taken up by or destroy the natural flora and fauna.
C. Wetlands
A -wetland is an area covered by water that supports aquatic vegetation.
Includes a broad range of habitats from periodically flooded regions to soil that is permanently saturated during growing season.
Conditions favor hydrophytes which are plants specially adapted to grow in water or soil periodically anaerobic due to being saturated with water.
=> Cattails, pond lilies, and sedges are examples of hydrophytes.
Both the hydrology and the vegetation are important determinants in wetland classification.
A wide variety of wetlands has been recognized although they form in one of only three topographic situations:
Basin wetlands develop in shallow basins ranging from upland depressions to lakes and ponds that have filled in.
Riverine wetlands develop along shallow and periodically flooded banks of streams and rivers.
Fringe wetlands are found along coasts of large lakes and seas where rising lake levels or tides cause water to flow back and forth.
=> Fringe wetlands include both freshwater and marine habitats. => Marine wetlands are closely linked to estuaries.
The types of plants present in a wetland are determined by the flow of water through the habitat.
The duration, frequency, and depth of water, as well as, the flood season are also important.
Wetlands are among the richest and valuable of biomes.
A diverse invertebrate community is present which supports a wide variety of birds.
A variety of herbivorous species consume the algae, detritus, and plants.
They provide water storage basins that reduce the intensity of flooding.
They improve water quality by filtering pollutants.
Although many wetlands have been destroyed for agriculture and development, a move to protect the remaining wetlands is underway.
D. Estuaries
An estuary is the area where a freshwater stream or river merges with the ocean.
Often bordered by salt marshes or intertidal mudflats.
Salinity varies spatially within the estuary from nearly fresh water to ocean water;
varies daily in these areas due to rise and fall of tides.
Estuaries are very productive due to nutrients brought in by rivers.
Because of their productivity, estuaries have a diverse flora and fauna.
Salt marsh grasses, algae, and phytoplankton are the major producers.
Many species of annelids, oysters, crabs, and fish are also present.
Many marine invertebrates and fish breed in estuaries or migrate through them to freshwater habitats upstream.
A large number of water fowl and other semiaquatic vertebrates use estuaries as feeding areas.
Human activities are having a large impact on estuaries.
Estuaries receive the pollutants dumped into the streams and rivers that feed them.
Residential and commercial development not only adds to pollution but eliminates some estuaries due to land filling.
E. Marine Zones: An Introduction
Marine communities are classified based on the depth at which they occur, their distance from shore, and light penetration.
A photic zone is present and extends to the depth at which light penetration supports photosynthesis; occupied by phytoplankton, zooplankton, and many fish species.
The aphotic zone is below the level of effective light penetration and represents a majority of the ocean's volume.
The intertidal zone is the shallow zone where terrestrial habitat meets the ocean's water.
The neritic zone extends from the intertidal zone, across the shallow regions, to the edge of the continental shelf.
The oceanic zone extends over deep water from one continental shelf to another;
reaches great depth.
Pelagic zone refers to open waters of any depth.
Benthic zone refers to the seafloor.
F. The Intertidal Zones
Intertidal zones, where land and sea meet, are alternately submerged and exposed by daily tide cycles.
Organisms in this zone are exposed to variations in temperature and availability of sea water.
These organisms are also subjected to the mechanical forces of wave action.
Rocky intertidal zones are vertically stratified and inhabited by organisms that possess structural adaptations that allow them to remain attached in this harsh environment.
The uppermost zone is submerged only by the highest tides and is occupied by relatively few species of algae, grazing mollusks, and suspension-feeding barnacles.
=> These organisms have various adaptations to prevent dehydration.
The middle zone is exposed at low tide and submerged at high tide.
=> Many species of algae, sponges, sea anemones, barnacles, mussels, and other invertebrates are found in this area.
=> The diversity is greater here due to the longer time spans this area is submerged.
Tide pools are often found in the middle zone.
=> These are depressions which are covered during high tide and remain as pools during low tide.
=> Tidepool organisms face dramatic salinity increases as water evaporates at low tide.
The low intertidal zone is exposed only during the lowest tides and shows the greatest diversity of invertebrates, fishes, and seaweeds.
Sandy intertidal zones and mudflats do not show a clear stratification.
Wave action continually shifts sand or mud particles; few algae or plants are present.
Predatory crustaceans and many suspension-feeding worms and clams burrow into the sand or mud and feed when the tide submerges the area.
Predatory or scavenging crabs and shorebirds often feed on burrowing organisms in these areas.
The diversity of intertidal zones is being reduced by human impact.
Oil pollution destroys many species.
Polluted water, old fishing lines, and plastic debris is harmful to most species.
Recreational use of these areas has greatly reduced the number of beach-nesting birds and turtles.
G. Coral Reefs
Coral reefs are found in the neritic zone of warm tropical waters where sunlight penetrates to the ocean floor.
Sunlight penetration permits photosynthesis and a constant supply of nutrients is provided by currents and waves.
Coral reefs are dominated by the structure of the coral. This diverse group of cnidarians secretes a hard, calcium carbonate external skeleton that provides a substrate on which other corals, sponges, and algae grow. (See Campbell, Figure 46.28)
The cnidarian coral animals feed on microscopic organisms and organic debris even though they are dependent on the photosynthetic products of their symbiotic dinoflagellate algae.
Coral reefs are very diverse and productive.
=> A large variety of microorganisms, invertebrates, and fish are found among the coral and algae.
Many herbivorous snails, sea urchins, and fish are present along with predators such as the octopus, sea stars, and many carnivorous fish.
Although many coral reefs are very large, they are delicate and can be severely damaged or destroyed by pollution, human induced damage, or introduced predators.
H. The Oceanic Pelagic Biome
The oceanic pelagic biome consists of the open waters far from shore.
The area is constantly mixed by circulating ocean currents.
Nutrient content is usually very low due to the sinking of the remains of organisms out of the zone to the lower benthic regions.
=> In tropical waters, nutrient content of this area is very low due to a permanent thermal stratification which prevents nutrient exchange with the deep waters.
=> In some areas of the temperate oceans, periodic upwellings carry nutrients from the bottom to the surface during the spring.
Waters are generally cold, although temperatures vary with latitude and depth.
Plankton is prevalent in this zone.
Photosynthetic phytoplankton grow and reproduce in the photic region (top 100m) of this biome.
Zooplankton (which graze on the phytoplankton) includes protozoans, copepods, krill, jellyfish, and larvae of many invertebrates and fishes.
Most species stay afloat in this zone through the aid of morphological structures like bubble-trapping spines, lipid droplets, gelatinous capsules, and air bladders.
Nekton (free-swimming animals) are also found in the oceanic pelagic biome.
Large squid, fishes, sea turtles, and marine mammals feed in this area.
Many fish are adapted to and live in the aphotic region of the pelagic zone.
=> Some have large eyes allowing them to see in dim light, while others have luminescent organs used to attract mates and prey.
Many pelagic bird species also feed on fish in this region.
Many migratory marine animals move through this region either following available food or moving from summer breeding to winter feeding areas.
I. Benthos
Benthos refers to those organisms which inhabit the benthic zone, the ocean bottom below both the neritic and pelagic zones.
The benthic zone receives nutrients in the form of detritus which settles into the area from the waters above.
Light and temperature decline rapidly from shallow, near-shore benthic areas to the ocean's depths.
The benthic zone substrate may be sand or very fine sediment composed of silt and shells of dead microscopic organisms.
Neritic benthic communities are diverse and productive.
Many bacteria, fungi, seaweeds, filamentous algae, and sponges are found here.
Sea anemones, worms, clams, various echinoderms and fishes are usually present.
Many of the species present are burrowing forms.
The composition of the community varies with distance from shore, water depth, and bottom composition.
Deep benthic communities living in the abyssal zone are exposed to very different conditions than those under the neritic and pelagic zones.
Water temperature is continuously cold (3°C), water pressure is extremely high, there is very little (if any) light, and low nutrient concentrations are typical.
Oxygen is usually present and a fairly diverse community of invertebrates and fishes are found.
The deep-sea hydrothermal vent communities are found along midocean ridges in this region.
=> These vent communities include chemoautotrophie bacteria as the primary
producers in place of photosynthesizing organisms.
=> These bacteria obtain energy by oxidizing H^S which forms by a reaction of the hot vent water with dissolved sulfate.
=> The bacteria are consumed by a variety of giant polychaete worms, arthropods, echinoderms, and fishes.
Ch. 46
OBJECTIVES
1. Explain why the field of ecology is a multidisciplinary science.
2. Distinguish among physiology, ecology, community ecology, and ecosystem ecology.
3. Describe the relationship between ecology and evolution.
4. Explain the importance of temperature, water, light, soil, and wind to living organisms.
5. Explain the Principle of Allocation.
6. Describe how environmental changes may produce behavioral, physiological, morphological, or adaptive responses in organisms.
7. Explain the concept of environmental grain and under what situation(s) a single environment may be both coarse-grained and fine-grained.
8. Describe the characteristics of the major biomes: tropical forest, savanna, desert, chaparral, temperate grassland, temperate forest, taiga, and tundra.
9. Compare and contrast the types of freshwater communities.
10. Using a diagram, identify the various zones found in the marine environment.