11 Ecology


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11 Ecology

  1. 1. Ecology Ecology is the study of the relationships between organisms and their physical and biotic environment: Relationships involve interactions with the physical world as well as interrelationships with other species and individuals of the same species. O 2 Nutrients CO 2
  2. 2. Living organisms can be studied at different levels of complexity. From least to most complex, these levels are (in an ecological context): Individual Population Community Ecosystem Biome Biological Complexity Biosphere Biome Ecosystem Community Population Individual
  3. 3. The biosphere is the region within which all living things are found on Earth. It is the narrow belt around the Earth extending from the bottom of the oceans to the upper atmosphere. The Biosphere
  4. 4. Ecosystems Light intensity varies Flow rate varies Rainfall level varies An ecosystem includes: all of the organisms (the community) … and their physical environment. There are many different sorts of ecosystems from natural to artificial, and they range in size from large to small. Still water habitatFast flowing water habitat Rock habitat Stream bank habitat
  5. 5. A community is a naturally occurring group of organisms living together as an ecological entity; the biological part of the ecosystem. Communities A nudibranch snail feeding on rock encrusting organisms
  6. 6. Abiotic (physical) factors are the influences of the non-living parts of the ecosystem. Examples include pH, salinity, temperature, turbidity, wind speed and direction, humidity, precipitation, water pressure, and light intensity and quality. Biotic factors are the influences of the living parts of the ecosystem. Producers and consumers interact as competitors, parasites, pathogens, symbionts, and predators. Factors Affecting Ecosystems
  7. 7. Physical environment Community Abiotic factors atmosphere, soil, water, wind speed wind direction, current velocity Biotic factors competitors, symbionts, predators, parasites, pathogens Ecosystem
  8. 8. The physical environment refers to the physical surroundings of any organism, including: the medium, e.g. water substrate, e.g. soil climatic (atmospheric) conditions light … and other physical properties. Environments
  9. 9. The type and extent of vegetation in a particular ecosystem is determined by physical factors on both a large scale and on a very localized (microclimate) level. Vegetation patterns are governed largely by climate (which is broadly related to latitude) and altitude. Climate and Vegetation Temperate climate High latitude climate
  10. 10. Tropical evergreen forests are found in equatorial regions where total annual rainfall exceeds 250 cm and the dry season lasts for no more than 2-3 months. These forests are species-rich. The climate is warm and rainy all year round. Tropical Rainforests
  11. 11. Rainforest Communities Dominant plants Trees and vines Floral richness Extremely high; the richest of all biomes. Faunal richness Extremely rich in mammals, birds, amphibians, and arthropods.
  12. 12. Temperature range: 2.2°C Annual total rainfall: 262 cm Example: Iquitos, Peru 3°S Physical Factors in Tropical Rainforests
  13. 13. The high species diversity of tropical rainforests can be supported because of the wide variety of microhabitats provided by the layered structure of the forest. The physical conditions at the uppermost level are quite different to those at the forest floor with respect to light intensity (and quality), wind speed, and humidity. A Tropical Rainforest Canopy Subcanopy Understorey Ground layer
  14. 14. Rainforest Factors Light: 70% Wind: 15 kmh-1 Hum: 67% Light: 50% Wind: 12 kmh-1 Hum: 75% Light: 12% Wind: 9 kmh-1 Hum: 80% Light: 6% Wind: 5 kmh-1 Hum: 85% Light: 1% Wind: 3 kmh-1 Hum: 90% Light: 0% Wind: 0 kmh-1 Hum: 98% Light: light intensity Wind: wind speed Hum: humidity
  15. 15. The ecological niche describes the functional position of an organism in its environment. A niche comprises: the habitat in which the organism lives. the organism’s activity pattern: the periods of time during which it is active. the resources it obtains from the habitat. Ecological Niche Adaptations Physical conditions Activity patterns Presence of other organisms Habitat
  16. 16. The physical conditions influence the habitat in which an organism lives. These include: substrate humidity sunlight temperature salinity pH (acidity) exposure altitude depth Physical Conditions
  17. 17. The law of tolerance states that “For each abiotic factor, an organism has a range of tolerances within which it can survive.” Law of Tolerance Examples of abiotic factors that influence size of the realized niche: Tolerance range Optimum range Unavailabl e niche Marginal niche Numberoforganisms Preferre d niche Marginal niche Unavailable niche
  18. 18. An organism’s habitat is the physical place or environment in which it lives. Organisms show a preference for a particular habitat type, but some are more specific in their requirements than others. Habitat Lichens are found on rocks, trees, and bare ground. Most frogs, like this leopard frog, live in or near fresh water, but a few can survive in arid habitats.
  19. 19. An organism’s habitat is not always of a single type. Some organisms occupy a range of habitats. There are various reasons why: Highly adaptable in habitat requirements. Different, but equivalent, resources available in different habitats. Reduced competition for resources in sub-optimal habitats. Habitat extremes may influence growth form, especially in plants. Habitat Range
  20. 20. Dingoes are a highly adaptable species found throughout Australia in ecosystems as diverse as the tropical rainforests of the north and the arid deserts in the central Australia. Within each of these ecosystems, they may occupy a range habitats, each one offering slightly different resources. Dingo Habitats
  21. 21. A microhabitat describes the precise location within a habitat where a species is normally found. It is a small, often highly specialized, and effectively isolated location. The term microhabitat generally applies to invertebrates which do not forage widely. Example: Within a woodland habitat, woodlice may be found in the microhabitat provided beneath the bark of the rotting wood. Microhabitats Woodlouse
  22. 22. An adaptation (or adaptive feature) is an inherited feature of an organism that enables it to survive and reproduce in its habitat. Adaptations are the end result of the evolutionary changes that a species has gone through over time. Adaptations may be: behavioral physiological structural Adaptations Osprey: a diurnal bird of prey Spotted owl: a nocturnal bird of prey
  23. 23. Organisms have adaptations for: Biorhythms and activity patterns, e.g. nocturnal behavior Locomotion (or movement) Defense of resources Predator avoidance Reproduction Feeding These categories are not mutually exclusive. Purposes of Adaptations
  24. 24. Structural adaptations: physical features of an organism, e.g. presence of wings for flight. Behavioral adaptations: the way an organism acts, e.g. mantid behavior when seeking, capturing, and manipulating prey. Functional (physiological) adaptations: those involving physiological processes, e.g. the female mantid produces a frothy liquid to surround and protect the groups of eggs she lays. Types of Adaptations Praying mantis
  25. 25. The adaptations found in plants reflect both the plant’s environment and the type and extent of predation to which the plant is subjected. Many plant adaptations are concerned with maintaining water balance. Terrestrial plant species show a variety of structural and physiological adaptations for water conservation. Plants evolve defenses, such as camouflage, spines, thorns, or poisons, against efficient herbivores. Plant Adaptations
  26. 26. Mangrove Adaptations Water level at high tide Prop roots descend from the trunk to provide additional support. Salt may accumulate in older leaves before they fall. Specialized root membranes in some mangroves prevent salt from entering their roots (salt excluders). Salt glands in the surface layers of leaves secrete salt (salt excretors). Cable roots radiate from the trunk. Fine feeding-roots grow off these radial roots and create a stable platform. Oxygen diffuses through the spongy tissue of the pneumatophore to the rest of the plant. Pneumatophores (breathing roots) arise from the cable roots.
  27. 27. Tropical forest plants live in areas of often high rainfall. Therefore, they have to cope with high transpiration rates. Tropical Forest Plants Shallow fibrous root system Funnel shaped leaves channel rain Water table high Water loss by transpiration
  28. 28. Ocean margin plants, e.g. intertidal seaweeds and mangroves, must cope with high salt content in the water. Ocean Margin Plants Mangrove pneumatophores Some mangrove species take in brackish water and excrete the salt through glands in the leaves. Seaweeds growing in the intertidal zone tolerate exposure to the drying air every 12 h.
  29. 29. Structural Adaptations in Rabbits Structural adaptations Widely spaced eyes gives a wide field of vision for surveillance of the habitat and detection of danger. Long, mobile ears enable acute detection of sounds from many angles for predator detection. Long, strong hind legs and large feet enable rapid movement and are well suited to digging. Cryptic coloration provides effective camouflage in grassland habitat. Rabbits are colonial mammals that live underground in warrens and feed on a wide range of vegetation. Many of their more obvious structural adaptations are associated with detecting and avoiding predators.
  30. 30. Functional Adaptations in Rabbits Functional (physiological) adaptations are associated with physiology. The functional adaptations of rabbits are associated with detecting and avoiding predation, and maintaining populations despite high losses. Functional adaptations High reproductive rate enables rapid population increases when food is available. Keen sense of smell allows detection of potential threats from predators and from rabbits from other warrens. Microbial digestion of vegetation in the hindgut enables more efficient digestion of cellulose. High metabolic rate and fast response times enables rapid response to dangers. Hawks are major predators of rabbits
  31. 31. Behavioral Adaptations in Rabbits The behavioral adaptations of rabbits reflect their functional position as herbivores and important prey items in many food webs. Behavioral adaptations Freeze behavior when startled reduces the possibility of detection by wandering predators. Thumps the ground with hind legs to warn others in the warren of impending danger. Lives in groups with a well organized social structure that facilitates cooperative defense. Burrowing activity provides extensive underground habitat as refuge from predators. Freezing is a typical behavior when threatened
  32. 32. Competition describes the active demand between two or more organisms for a resource. Competition may be: Intraspecific: between individuals of the same species. Interspecific: between individuals of different species. Each competitor is inhibited in some way by the interaction. Competition Interspecific competition on a reef Intraspecific competition: hyaenas
  33. 33. Competition affects the size of a competitor’s realized niche. The effect is dependent on the intensity and type of the competition. Niches are narrower with moderate interspecific competition (Fig. 1). Intense interspecific competition results in a very narrow realized niche as species specialize to exploit a narrower range of resources (Fig. 2). Intense intraspecific competition results in a broader realized niche as individuals are forced to occupy suboptimal conditions (Fig. 3). Competition and Niche Size Fig. 1 Fig. 2 Fig. 3 Narrower niche Broader niche Possible tolerance range Realized niche of species
  34. 34. Gause’s competitive exclusion principle states: “two or more resource-limited species, having identical patterns of resource use, cannot coexist in a stable environment: one species will be better adapted and will out-compete or otherwise eliminate the other(s)”. If two species compete for some of the same resources (e.g. food items of a particular size), their resource use curves will overlap. In the zone of overlap, interspecific competition is the most intense. Gause’s Principle Zone of overlap Species B Resource use as measured by food item size Amounteaten Species A
  35. 35. Interspecific competition is usually less intense than intraspecific competition because niche overlap between species is not complete. Species with similar ecological requirements may reduce competition by exploiting different microhabitats within the ecosystem. Example: Ecologically similar damsel fish at Heron Island, Queensland, Australia exploit different resources or regions over the coral reef. Niche Differentiation Sea levelReef crest Pw Pomacentrus wardi Pf Pomacentrus flavicauda Pb Pomacentrus bankanensis Sa Stegastes apicalis Pl Plectroglyphidodon lacrymatus Ef Eupomacentrus fasciolatus Eg Eupomacentrus gascoynei Gb Glyphidodontops biocellatus
  36. 36. In the eucalypt forests of eastern Australia different bird species forage at different heights in the forest. This selective foraging behavior reduces niche overlap between species that might otherwise compete directly. Competition in Eucalypts Key to bird species Yellow- throated scrubwren Brown thornbill Spine-tailed swift Striated thornbill Leaden flycatcher Ground thrush Rufous fantail White-throated treecreeper Ys Bt Sw Lf St Gt Rf Wt
  37. 37. Organisms do not generally live alone. A population is a group of organisms from the same species occupying in the same geographical area. This area may be difficult to define because: A population may comprise widely dispersed individuals which come together only infrequently, e.g. for mating. Populations may fluctuate considerably over time. Populations Migrating wildebeest populationMigrating wildebeest population Tiger populations compriseTiger populations comprise widely separated individualswidely separated individuals
  38. 38. Populations are dynamic and exhibit attributes that are not shown by the individuals themselves. These attributes can be measured or calculated and include: Population size: the total number of organisms in the population. Population density: the number of organisms per unit area. Features of Populations 1
  39. 39. Features of Populations 2 Population composition provides information relevant to the dynamics of the population, i.e. whether the population is increasing or declining. Information on population composition (or structure) includes: Sex ratios: the number of organisms of each sex. Fecundity (fertility): the reproductive capacity of the females.
  40. 40. The study of changes in the size and composition of populations, and the factors influencing these changes, is population dynamics. Key factors for study include: Population growth rate: the change in the total population size per unit time. Natality (birth rate): the number of individuals born per unit time. Population Dynamics Population size is influenced by births…Population size is influenced by births… ……and deathsand deaths
  41. 41. Migration Migration is the movement of organisms into (immigration) and out of (emigration) a population. It affects population attributes such as age and sex structure, as well as the dynamics of a population. Populations lose individuals through deaths and emigration. Populations gain individuals through births and immigration. Migrating species may group together to form large mobile populations WildebeestWildebeest Canada geeseCanada geese
  42. 42. The number of individuals per unit area (for terrestrial organisms) or volume (for aquatic organisms) is termed the population density. At low population densities, individuals are spaced well apart. Examples: territorial, solitary mammalian species such as tigers and plant species in marginal environments. At high population densities, individuals are crowded together. Examples: colonial animals, such as rabbits, corals, and termites. Population Density High density populations Low density populations
  43. 43. A crude measure of population density tells us nothing about the spatial distribution of individuals in the habitat. The population distribution describes the location of individuals within an area. Distribution patterns are determined by the habitat patchiness (distribution of resources) and features of the organisms themselves, such as territoriality in animals or autotoxicity in plants. Individuals in a population may be distributed randomly, uniformly, or in clumps. Population Distribution More uniform distribution in cacti Clumped distribution in termites
  44. 44. A population’s distribution is considered random if the position of each individual is independent of the others. Random distributions are not common; they can occur only where: The environment is uniform and resources are equally available throughout the year. There are no interactions between individuals or interactions produce no patterns of avoidance or attraction. Random distributions are seen in some invertebrate populations, e.g. spiders and clams, and some trees. Random Distribution Spider populations appear to show a random distribution
  45. 45. Uniform or regular distribution patterns occur where individuals are more evenly spaced than would occur by chance. Regular patterns of distribution result from intraspecific competition amongst members of a population: Territoriality in a relatively homogeneous environment. Competition for root and crown space in forest trees or moisture in desert and savanna plants. Autotoxicity: chemical inhibition of plant seedlings of the same species. Uniform Distribution Saguaro cacti compete for moisture and show a uniform distribution
  46. 46. Clumped distributions are the most common in nature; individuals are clustered together in groups. Population clusters may occur around a a resource such as food or shelter. Clumped distributions result from the responses of plants and animals to: Habitat differences Daily and seasonal changes in weather and environment Reproductive patterns Social behavior Clumped Distribution Sociality leads to clumped distribution
  47. 47. Calculating Population Change Births, deaths, and net migrations determine the numbers of individuals in a population Emigration (E) Births (B) Immigration (I) Deaths (D)
  48. 48. Rates of Population Change Ecologists usually measure the rate of population change. These rates are influenced by environmental factors and by the characteristics of the organisms themselves. Rates are expressed as: Numbers per unit time, e.g. 2000 live births per year Per capita rate (number per head of population), e.g. 122 live births per 1000 individuals (12.2%) Many invertebrate populations increase rapidly in the right conditions Large mammalian carnivores have a lower innate capacity for increase
  49. 49. Populations becoming established in a new area for the first time are often termed colonizing populations. They may undergo a rapid exponential (logarithmic) increase in numbers to produce a J-shaped growth curve. In natural populations, population growth rarely continues to increase at an exponential rate. Factors in the environment, such as available food or space, act to slow population growth. Exponential Growth Colonizing Population Here the number being added to the population per unit time is large. Exponential (J) curve Exponential growth is sustained only when there are no constraints from the environment. Here, the number being added to the population per unit time is small. Lag phas e Populationnumbers(N) Time
  50. 50. Logistic Growth As a population grows, its increase will slow, and it will stabilize at a level that can supported by the environment. This type of sigmoidal growth produces the logistic growth curve. Environmental resistance increases as the population overshoots K. Environmental resistance decreases as the population falls below K. Established Population Carrying capacity (K) The population density that can be supported by the environment. The population tends to fluctuate around an 'equilibrium level'. The fluctuations are caused by variations in the birth rate and death rate as a result of the population density exceeding of falling below carrying capacity. In the early phase, growth is exponential (or nearly so) Lag phase Logistic (S) curve As the population grows, the rate of population increase slows, reaching an equilibrium level around the carrying capacity. Populationnumbers(N) The population encounters resistance to exponential growth as it begins to fill up the environment. This is called environmental resistance. Time
  51. 51. Two parameters govern the logistic growth of populations. The intrinsic rate of natural increase or biotic potential. This is the maximum reproductive potential of an organism, symbolized by the letter r. The saturation density or carrying capacity of the environment, represented by the letter, K. We can characterize species by the relative importance of r and K in their life cycles. ‘r’ and ‘K’ Selection r-selected species These species rarely reach carrying capacity (K). Their populations are in nearly exponential growth phases for much of the year. Early growth, rapid development, and fast population growth are important. K-selected species These species exist near asymptotic density (K) for most of the time. Competition and effective use of resources are important. Time Populationnumbers(N)
  52. 52. r-Selected Species Species with a high intrinsic capacity for population increase are called r-selected or opportunistic species. These species show certain life history features and, to survive, must continually invade new areas to compensate for being displaced by more competitive species. Climate Variable and/or unpredictable Mortality Density-independent Survivorship Often type III (early loss) Population size Fluctuates wildly. Often below K. Competition Variable, often lax. Generalist niche. Selection favors Rapid development, high rm, early reproduction, small body size, single reproduction (annual) Length of life Short, usually less than one year Leads to: Productivity
  53. 53. K-Selected Species Species that are K-selected exist under strong competition and are pushed to use available resources more efficiently. These species have fewer offspring and longer lives. They put their energy into nurturing their young to reproductive age. K-selected species include most large mammals, birds of prey, and large, long-lived plants. Climate Fairly constant and/or predictable Mortality Density-dependent Survivorship Usually types I and II (late or constant loss) Population size Fairly constant in time. Near equilibrium with the environment. Competition Usually keen. Specialist niche. Selection favors Slower development, larger body size, greater competitive ability, delayed reproduction, repeated reproductions Length of life Longer (> one year) Leads to: Efficiency
  54. 54. No organism exists in isolation. Each participates in interactions with other organisms and with the abiotic components of the environment. Species interactions may involve only occasional or indirect contact (predation or competition) or they may involve a close association between species. Symbiosis is a term that encompasses a variety of such close associations, including parasitism (a form of exploitation), mutualism, and commensalism. Species Interactions Oxpecker birds on buffaloCanopy tree with symbionts attached
  55. 55. Types of Interaction
  56. 56. Parasitism Many animal taxa have representatives that have adopted a parasitic lifestyle. Parasites occur more commonly in some taxa than in others. Insects, some annelids, and flatworms have many parasitic representatives. Parasites live in or on a host organism. The host is always harmed by the presence of the parasite, but it is not usually killed. Both parasite and host show adaptations to the relationship. Parasites may live externally on a host as ectoparasites, or within the host’s body as endoparasites. Tick ectoparasite on bird wing Many birds and mammals use dust bathing to rid themselves of external parasites
  57. 57. Mutualistic relationships occur between some birds (such as oxpeckers) and large herbivores (such as zebra, Cape buffalo, and rhinoceros). The herbivore is cleaned of parasites and the oxpecker gains access to food. Lichens are an obligate mutualism between a fungus and either a green alga or a cynobacterium. The fungus obtains organic carbon from the alga. The alga obtains water and nutrient salts from the fungus. Mutualistic Relationships Lichen: an obligate mutualism Cape buffalo and oxpecker birds
  58. 58. In commensal relationships, one party (the commensal) benefits, while the host is unaffected. Epiphytes (perching plants) gain access to a better position in the forest canopy, with more light for photosynthesis, but do no harm to the host tree. Commensal anemone shrimps (Periclimenes spp.) live within the tentacles of host sea anemones. The shrimp gains protection from predators, but the anemone is neither harmed nor benefitted. Commensal Relationships
  59. 59. Competition is one of the most familiar of species relationships. It occurs both within (intraspecific) and between (interspecific) species. Individuals compete for resources such as food, space, and mates. In all cases of competition, both parties (the competitors) are harmed to varying extents by the interaction. Neighboring plants compete for light, water, and nutrients. Interactions involving competition between animals for food are dominated by the largest, most aggressive species (or individuals). Competition
  60. 60. Intraspecific Competition Environmental resources are finite. Competition within species for resources increases as the population grows. At carrying capacity (K), it reduces the per capita growth rate to zero. When the demand for a resource (e.g. water, food, nesting sites, light) exceeds supply, that resource becomes a limiting factor. Animals compete for resources such as water (left) or mates (right), especially when these are in short supply or access to them is restricted.
  61. 61. Most predators have more than one prey species, although one may be preferred. As one prey species becomes scarce, predation on other species increases (prey switching), so the proportion of each prey species in the predator’s diet fluctuates. Where one prey species is the principal food item, and there is limited opportunity for prey switching, fluctuations in the prey population may closely govern predator cycles. Predator-Prey Interactions
  62. 62. The Role of Prey Switching Vertebrate predators rarely control their prey populations. Prey species tend to show regular population cycles in response to other factors and predators track these cycles. Predators usually have a preferred prey species, but will switch to other prey when that species is rare. Generalist predators can maintain stable populations by prey switching in response to changing prey densities. Voles are the preferred prey of red foxes, but they will take other prey as well Brown bears are true generalists and feed according to availability
  63. 63. Predator-Prey Cycles Mammals frequently exhibit marked population cycles of high and low density that have a certain, predictable periodicity. Regular trapping records of the Canada lynx over a 90 year period revealed a cycle of population fluctuations that repeated every 10 years or so (below). These oscillations closely matched, with a lag, the cycles of their principal prey item, the snowshoe hare.