Zoology Chapter 2 Notes
Zoology Chapter 2 Notes ZOO1010C
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This 10 page Class Notes was uploaded by Laura Drury on Sunday September 25, 2016. The Class Notes belongs to ZOO1010C at Hillsborough Community College taught by Dr. Peter Sleszynski in Fall 2016. Since its upload, it has received 7 views. For similar materials see General Zoology in Animal Science and Zoology at Hillsborough Community College.
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Date Created: 09/25/16
Chapter 2: Animal Ecology Ecological Niche and Animal Species Diversity Life's diversity is organized into a hierarchy of interacting units o Individual organism o Population o Community o Ecosystem Central to ecological study of animal diversity is habitat, the spatial location where an animal lives o What an animal does in its habitat is its niche How it gets food How it reproduces o As a species evolves, so does its niche, and no 2 species in a community can evolve to exploit exactly the same resources at the same place and time Illustrates the "competitive exclusion principle" : no 2 species can occupy the same niche if they are to live together in a stable ecological community Ernst Haeckel o German zoologist o Mid-19th century o Introduced term ecology, the relation of the animal to its organic as well as inorganic environment o Animal ecology now incorporates the behavior, physiology, genetics, and evolution of animals to study interactions between populations of animals and their environment o Major goal is to explain how these diverse interactions influence the geographical distribution and abundance of animal populations Ecology encompasses a hierarchy of biological systems in interaction with their environments At the base of the hierarchy is an organism such as an individual animal To understand why animals live where they do, ecologist examine the varied physiological and behavioral mechanisms that animals use to grow, survive, and reproduce o An animals physiological capacities permit it to occupy changing and often adverse environments o Behavioral responses are important also for obtaining food, finding shelter, escaping enemies and unfavorable environments, finding a mate, courting, and tending to offspring o Ecologists who focus their studies at the organismal level are called physiological ecologists or behavioral ecologists Animals in nature coexist with others of the same species as reproductive units called populations o Populations have properties that can't be discovered by studying individuals alone o Ex. Polymorphism, gene pool, growth in numbers over time, and factors that limit the density of individuals in a given area Populations of different species co-occur in more complex associations called ecological communities o One measure of an ecological community's complexity is the number of species present, called species richness o The populations of species in a community interact with one another in many ways, most prevalent ones being predation, parasitism, and competition Predators obtain energy and nutrients by killing and eating prey Parasites derive similar benefits from their host organism, but they live on or in the host and usually do not kill the host A parasitoid lives on or in a host but eventually kills its host organism o Competition occurs when food and/or space are limited and members of different species interfere with each other's use of their shared resources Communities are complex because all of these interactions occur simultaneously, and their individual effects on the community cannot be isolated Ecological communities are biological components of even larger, more complex entities called ecosystems o Consists of all populations in an ecological community and their physical environment o Study of ecosystems reveals 2 key processes in nature: The flow of energy and the cycling of materials through biological channels o Largest ecosystem is the biosphere, the thin veneer of land, water, and atmosphere that envelops the earth and supports all life Environment and the Niche An animal's environment compromises all conditions that directly affect its chances for survival and reproduction o These factors include space; forms of energy such as sunlight, heat, wind, and water currents; and materials such as soil, air, water, and numerous chemicals Environment also includes other organisms, which can be an animal's food or it's predators, competitors, hosts, or parasites Environment thus includes abiotic (nonliving) and biotic (living) factors Resources, such as space and food, are the factors that an animal uses directly o Resource can be expendable (such as food) or nonexpendable (such as a nest) If we consider all environmental conditions that permit members of a species to survive and to multiply, we define a role for that species in nature distinct from those of other species. This is called a niche o An animals fundamental niche is it's potential rose, and its realized niche is the subset of potentially suitable environments that an animal actually experiences o Likewise, we must distinguish fundamental niche from realized niche at the population and species level Ex. Competition within a community may limit the realized niche of a species to a much smaller range of conditions that those predicted by its fundamental niche Populations A population is a reproductively interactive group of animals of a single species A geographically and genetically cohesive population that is separable from other such populations is called a deme o Because members of a deme regularly interbreed, they share a common gene pool Movement of individuals among demes within a species can impart some evolutionary cohesion to the species as a whole o Local environments can change unpredictable, sometimes depleting or eliminating a local deme o Immigration is a crucial source of replacement among demes within a region o A species can avoid extinction if risk of extinction is spread among many demes Simultaneous destruction of the environments of all demes is unlikely unless a catastrophe is geographically widespread o Interaction among demes in this matter is called metapopulation dynamics "metapopulation" denotes a population subdivided into multiple genetically interacting demes o In some species, gene flow and recolonization among demes are nearly symmetrical If some demes are stable and others more susceptible to extinction, the more stable ones (source demes) differentially supply emigrants to the less stable ones (sink demes) Each population or deme has a characteristic age structure, sex ratio, and growth rate o Demography is the study of these properties and the factors that influence them o Demographic characteristics (individual size, age, number of offspring) vary according to the lifestyles of the species under study o Some animals are modular Such as sponges, corals, and ectoprocts Form colonies of genetically identical organisms Reproduction is by asexual cloning Colonies propagate also by fragmentation, as seen on coral reefs Age structure and sex ratio are difficult to measure Changes in colony size are used to measure growth rate as an alternative to counting individuals and measuring their ages and number of offspring o Most animals are unitary Even some unitary species reproduce by pathogenesis Usually such groups contain only females, which lay unfertilized eggs that hatch into daughters genotypically identical to their mothers o Most animals are biparental, and reproduction follows a period of organismal growth and maturation Each new generation begins with a cohort of individuals born at the same time Not all individuals of a cohort survive to reproduce For population to retain constant size, each female must replace herself with 1 daughter that survives to reproduce If females produce more than one viable daughter, population grows. If less, it declines Animal species have different characteristic patterns of survivorship from birth until death of the last members of a cohort o Semelparity is the condition in which an organism reproduces only once during its life history o Iteroparity denotes the occurrence of more than one reproductive cycle in an organism's life Populations of animals containing multiple cohorts (robins, box turtles, and humans) exhibit age structure Population Growth and Intrinsic Regulation Population growth is the difference between rates of birth and death o All populations have an inherent ability to grow exponentially This ability is called intrinsic growth rate If species constantly grew to their potential, we would run out of resources When resources are expended, the population would shrink down The limiting resource is the one in shortest supply relative to the population's needs The largest population that the limiting resource can support in a habitat is called the carrying capacity of the environment Extrinsic Limits to Growth Population growth also can be limited by extrinsic biotic factors, such as predation, parasitism (including disease-causing pathogens), and interspecific competition or by abiotic influences, such as floods, fires, and storms o Although abiotic factors reduce populations, they can't truly regulate population growth because their effect is wholly independent of population size Abiotic limiting factors are thus density-independent In contrast, biotic factors can and do act in a density-dependent manner o Predators and parasites respond to changes in density of their prey and host populations to maintain those populations at fairly constant sizes These sizes are below carrying capacity, because populations regulated by predation or parasitism are not limited by their resources Competition between species for a common limiting resource lowers the effective carrying capacity for each species below that of either one alone Community Ecology Interactions Among Populations in Communities Populations of animals that form an ecological community interact in various ways that can be detrimental (-), beneficial (+), or neutral (0) to each species, depending on the nature of the interaction o Detrimental (-) Ex. A predator's effect on prey, because survival of prey animal is reduced o Beneficial (+) Ex. The same interaction benefits the predator because the food obtained from prey increases the predator's chance for survival Thus, the predator-prey interaction is + - o + - interactions Parasitism is one example - in which parasite benefits by using the host as a home and a source of nutrition, and the host is harmed Herbivory, in which an animal eats a plant is another o 0 + Commensalism is an interaction that benefits one species and neither harms nor helps the other An example would be the bacteria that inhabit our intestinal tract Organisms engaged in mutualism ( + + ) both benefit from their ecological interaction o Some mutualistic relationships are necessary for survival of one or both species Termed obligatory mutualism Facultative mutualisms are not required for a species' survival Competition between species reduces fitness of both ( - - ) o Many biologists, including Darwin, considered competition the most common and important interaction of nature Ecologists have constructed most of their theories of community structure based on premise that competition is the chief organizing factor is the makeup of species This condition is called amensalism, or asymmetrical competition Competition and Resource Partitioning Competition occurs when 2 or more species share a limiting resource Sharing food or space alone with another species does not invite competition unless the resource is in short supply Competing species reduce conflict by reducing overlap of their niches o Niche overlap is the portion of resources shared by the niches of 2 or more species Ex. If 2 species of birds eat seeds of exactly the same size, competition eventually excludes the species less able to exploit the resource This example illustrates principle of competitive exclusion Strongly competing species cannot coexist indefinitely Principle discovered in 1932 by G.F. Gause o To coexist in the same habitat, species must specialize by partitioning a shared resource and using different portions of it. This is called resource partitioning Ecological character displacement is the mechanism of resource partitioning o Co-occurrence in the same community causes species to evolve niche dimensions more restricted than those of their ancestors An alternative and more common means of evolving resource partitioning is through microhabitat selection, formation of a community by species whose preferred microhabitats differ sufficiently to prevent them from competing for what otherwise would be a limited resource When several species share the same resources by partitioning, they form a guild o Species in an ecological guild share a common livelihood o Term guild was introduced to ecology in 1967 by Richard Root Predators and Parasites The ecological warfare waged by predators against their prey causes coevolution o Predators get better at catching prey and prey gets better at escaping its predators The war between predators and prey reaches high art in the evolution of defenses by potential prey o Potential prey can escape detection because their bodies match their background or resemble some inedible feature of the environment (called cryptic defenses) o Animals that are toxic or distasteful to predators advertise their strategy with bright colors and conspicuous behavior (called aposematic defenses) o When distasteful prey adopt warning coloration, advantages arise for palatable prey Palatable prey can deceive predators by mimicking distasteful prey, a phenomenon called Batesian mimicry Species of coral snakes and yellow jackets serve as models for other species, called mimics, which are harmless but resemble their harmful counterparts Another form of mimicry is Mullerian mimicry, when 2 or more species that are toxic or otherwise harmful mimic each other Sometimes one population's influence on others is so pervasive that its absence drastically changes the entire community, a keystone species o Keystone predators act by reducing prey populations below a level where resources are limiting o By reducing competition, keystone species allow more species to coexist on a resource o They contribute to maintaining diversity o They also illustrate a more general phenomenon, disturbance Periodic natural disturbances, such as floods or fires, can prevent monopolization of resources and competitive exclusion by a few broadly adapted competitors Disturbances can also permit more species to coexist in such highly diverse communities Parasites are often considered to be freeloaders because they appear to benefit from their hosts at no expense o Ectoparasites, such as ticks and lice, infest many different kinds of animals o Host provides nutrition from its body and aids dispersal of parasite o Endoparasites, such as tapeworms, have lost their ability to choose their habitat o Because they must move among hosts to complete their life cycle, the chance that a single organism will live to reproduce is very low Ecosystems Transfer of energy and materials among organisms within ecosystems is the ultimate level of organization in nature Energy and materials are required to construct and maintain life, and their incorporation into biological systems is called productivity o Ecologists subdivide productivity into component trophic levels based on how organisms obtain energy and materials o Trophic levels are linked together into food chains, which denote movement of energy from plant compounds to organisms that eat plants, then to other organisms that eat the plant feeders, and possibly further through a linear series of organisms that feed and are then eaten by others o A food web shows the branching pathways for transfer of energy and materials among species in an ecosystem o Primary producers are organisms that begin productivity by capturing energy from outside the ecosystem and using it to fix carbon, hydrogen, oxygen, nitrogen, phosphorous, and sulfur into the organic molecules of living systems Usually plants or algae that capture solar energy through photosynthesis Powered by solar energy, plants assimilate and organize minerals, water, and carbon dioxide into living tissue o All other organisms survive by consuming this tissue, or by consuming organisms that consumed this tissue Consumers include herbivores (which eat plants directly), and carnivores (which eat other plants) Most important consumers are decomposers, mainly bacteria and fungi that break dead organic matter into its mineral components, returning it to a soluble form available to plants at the base of the nutrient cycle Energy Flow and Productivity Every organism has an energy budget o Each organism must obtain enough energy to meet its metabolic costs, to grow, and to reproduce o Ecologists divide the budget into 3 main components Gross productivity Like gross income, it is the total energy assimilated, analogous to your pay before deductions Respiration Energy used for metabolic maintenance When an animal eats, it digests food and absorbs nutrients Net productivity An animal's "take home pay" Energy stores by an animal in its tissues as biomass Animals use this sort of energy for growth and reproduction Laws of Thermodynamics Scientists' observations of how heat and energy interact within a system revealed the laws of thermodynamics o The first law states that energy cannot be created or destroyed Although energy can change from one form to another, the total amount of energy in an isolated system remains unchanged The energy budget of every animal is finite and may be limiting Energy is available for growth of individuals and populations only after satisfying maintenance o Second law states that the total disorder or randomness of a closed system always increases Important when we study energy transfers between trophic levels in food webs Our ability to feed a growing human population is influenced profoundly by this law Ecological Pyramids When we examine the food chain in terms of biomass at each level, we can construct ecological pyramids either of numbers or of biomass o A pyramid of numbers, also called a Eltonian pyramid, depicts numbers of organisms that are transferred between each trophic level Provides a vivid impression of the great difference in numbers of organisms involved in each step of the chain, and it supports the observation that large predatory animals are rarer than small animals in which they feed o Pyramids of biomass are more instructive Depict the total bulk, or "standing crop", of organisms at each trophic level Such pyramids usually slope upward because energy is lost at each transfer, so there is less energy available to sustain production of biomass at each successively higher trophic level In aquatic ecosystems whose producers are algae, which have short lifespans and high turnover, the pyramid inverts o A third type is a pyramid of energy, which shows rate of energy flow between levels Never inverted because amount of energy transferred from each level is less than the amount that entered it Gives the best overall picture of community structure because it depicts the loss of energy from a community as energy flows from primary producers through the food web Nutrient Cycles All elements essential for life come from environmental air, soil, rocks, and water When plants and animals die and decay, their elements and inorganic compounds return to the environment Decomposers fill an essential role in this process by feeding on the remains and fecal material o Result is that nutrients flow in a perpetual cycle between biotic and abiotic components of the ecosystem Nutrient cycles are often called biogeochemical cycles because they involve exchanges between living organisms and the rocks, air, and water of the earth's crust Nutrient pools can be altered greatly by fertilizers and other compounds that people add to the soil o Our synthetic compounds often challenge nature's nutrient cycling because decomposers have not evolved ways to degrade them o Pesticides are among most harmful Genetic engineering of crop plants aims to improve their resistance to pests to lessen the need for chemical pesticides Biodiversity and Extinction Biodiversity exists because rates of speciation on average slightly exceed rates of extinction in earth's evolutionary history 99% of all species that have lived are extinct Speciation rates represent an ongoing process of geographic expansion of populations by dispersal followed by geographic fragmentation, producing a multiplication of species Extinction rates show episodic peaks and valleys throughout earths evolutionary history Fossil studies show that species whose geographic ranges are large have lower average rates of extinction than those with small geographic ranges, although mass extinction can erase this contrast A paradox of biodiversity is that geographic habitat fragmentation of a species simultaneously increases rates of both local extinction and speciation Higher taxa, such as orders, families, and genera, also gain some protection from extinction by having large geographic ranges
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