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Biology (Sci)
BIOL 215
Neil Price

BIOL215 Lecture 13 Notes Population biology is the study of individuals from one species that live together in space and time (Book pg. 114) Basic demography is something that focuses on a species; not of a community Population is of a single species while community is formed of a few species interacting together in the same place and same time. Ecosystem incorporates the abiotic functions of communities in the same time and same place Population dynamics studies the "behavior" of populations such as increases and decreases in population size. Demography is the study of the age structure of population. It includes the study of death, birth, population growth, and population decrease When we're talking about demography, we must have a sense of the size of the population at a given time (initial time). We want to estimate how the population will grow to predict the population in the future. Very mathematical Consider births and immigration as factors that increase/brings individuals to a population Consider deaths and emigration as factors that decrease/take away individuals to a population Demography is the understanding of the balance between birth and death taking into account immigration and emigration Ecology means "the knowledge in the house" in Greek To measure populations: 1) census for humans, 2) quadrants for plants, 3) marked captures for birds, 4) marked capture (with tranquilizer) for deers See list of methods for measuring populations: pg. 120 Density of number of individuals per unit area is measure of population size. Individuals of small size are abundant on a small spatial scale and bigger individuals are less abundant The two most important tenants of demography are: death and birth Life table help to understand population growth. Life table is a table that records survivorship and mortality in a population Cohort table: follows all the individuals born at the same time from birth to death (very precise, but • complicated to do in nature because of long-lived species) Static table: snapshot of a population over a short time interval. All individuals are of different ages • See Table 8.3 to understand calculations for lx and qx A plot of number of survivors (Y-axis) vs. Age (X-axis) is a survivorship curve. It is used to understand how mortality changes with age in a population Survivorship is proportion of population surviving to each age Research in population ecology suggests that patterns of survivorship usually fall into three categories: • Type I: High juvenile survivorship (or low juvenile mortality) • Type II: Constant rates of survival • Type III: Low juvenile survivorship (or high juvenile mortality) Another method to represent the demography is by drawing age structure Age distribution consists of estimating the number of individuals of different age in a population. It corresponds to the static life table. Age distribution is less accurate then cohort table, but often much easier to obtain See Table 8.5 to see survivorship schedule (l ) axd fertility schedule (bx) The fecundity schedule is the table of values of (b ).b xs xhe average number of offspring produced by each female individual in each age interval Capacity for increase is calculated together by l andxb , whixh allows for estimating population growth Net reproductive rate is the sum of survivorship and reproduction for each age class: The rate of increase of populations needs to take into account generation time Generation time is calculated by this equation: G= ∑ xlx x where x is age between generations R0 Mean length of a generation, G, is mean period elapse between the "birth" of parent and "birth of offspring As generation time increases, population increase happens slower Knowing the net reproductive rate and generation time, we can calculate the instantaneous rate of increase of a population by the following equation: In the simplest case, (i.e. annual species, G = 1), therefore the instantaneous rate of increase: Net productive rate is calculated by: BIOL215 Lecture 14 Notes The rate of increase in a population that we are obtaining is the "instantaneous rate of increase" - at one specific point in time, how the population is increasing. The equation is: • In the case of an annual species that becomes the annual rate of increase (reproductive rate for an annual species is equal to the rate of increase per year of that population; is the simplest case) • In the simplest case, the annual species occurs when G=1 (one generation time) The instantaneous rate of increase is calculated by: We can use the rate of increase to build another measure of population growth or to develop an equation that will allow us to predict a population over time. We call this the geometric growth, calculated by: where r is intrinsic capacity for increase in a given environment Under a geometric growth: • Any population subject to fixed schedule of natality and mortality grows in geometric way • Geometric growth dictate fixed and unchanging age distribution, the stable age distribution • If the rate of increase is less than zero, the population will decrease • If the rate of increase is zero, the population will stay stable (same) If the rate of increase is one, the population will double If the rate of increase is greater than zero, the population will increase In geographic model, the population on the log scale increase always of the same amount per year or per time interval because r is fixed (therefore, linear curve) On an arithmetic scale, you have an exponential growth (a population that will increase and as you have more and more individuals, the increments will increase faster and faster) We look at population growth rate because it serves a great purpose in conservative ecology known as 'Minimum Viable Populations' Minimum viable populations are what you want to achieve if you are a conservation ecology and your purpose is to protect the species. You want to ensure the population size will persist for a specified time (100 years) Demographic stochasticity (stochasticity means phenomenon that comes by chance) Example: species that would reproduce and have many more males instead of balanced sex Is a factor that can explain population reducing in size Genetic stochasticity Example: female biased population will cause genetically similar offspring due to lack of gene pool, thus potential in-breeding Environmental stochasticity and natural catastrophes Are destructions of the environment that come in an unforeseen way. Less fit individuals will have a harder time surviving Vortex of extinction (good example comes from Heath hen extinction) The minimum viable population size is the size of the population to avoid starting this vortex that will lead the population to extinction In general for bird species, you need to have at least a population of 10,000 birds to avoid extinction. The MVP that we should try to maintain and protect are very high Deborah Rabinowitz's helps explain '7 forms of rarity' (rarity: the characteristics of being rare) based on 3 characteristics: • Local population size, • Habitat specificity (i.e. live only on coast) • Geographic range (i.e. located only in a certain region) Prairie chicken example shows how genetic stochasticity caused a declining population due to low percentage of hacked eggs because of limited gene pool, thus low fitness of survival. However, upon transporting the prairie chicken to Kansas and Minnesota where there was a population of prairie chicken, the increase in gene pool allowed the population to bounce back and an increase in percentage of eggs hatched For logistic growth, we know that populations grow exponentially: • At initial stages of colonization When conditions are favorable or, • • Sometimes, when recovering from damages However, natural populations cannot sustain exponential growth indefinitely Example of logistic growth is the story of peasants of Protection Island. In 1937, introduction of 8 pheasant. Island has no predators and lots of food. In 1942, predicted population size would be 1,488. the actual size was 1898 Logistic population growth (model): • As population size increases exponentially at the beginning, but growth eventually slows and ceases (growth will plateau) • The observed patter is sigmoidal or S-shaped The relationship of logistic growth is described by a modification of the exponential model in which a limit is added as seen below: Carrying capacity or K: the population size at which growth stops. In other words, K is the number of individuals of a particular population that the environment can support At carrying capacity, the population stops growing. You can possibly have a population that’s greater than the carrying capacity. However, as soon as the artificial factors that allowed the boom in population is removed, the population will go back to its carrying capacity As population size increases, growth increases increased as well. Growth reaches a maximum at half when the number of individuals is half of carrying capacity (N = K/2). Afterwards, population growth will decrease To recap, in geometric/exponential growth, we have a linear growth with r being independent of the size of the population. R is fixed. In logistic growth, the model equation shows that the population growth will decrease as the size of the population increases Carrying capacity is one of the most influential ecological concepts for today's society There are alternative models: • Theta logistic growth equation* (read in textbook) Time lag effects* (read in textbook) • • Stochastic models • Leslie matrix model From deterministic to probabilistic models (stochastic models), it is vital we talk about probabilistic models because biology is much more probabilistic than deterministic In deterministic model, there are a given number of individuals; there is a fixed growth rate so you can predict exactly what happens in the future. For deterministic models, there is exactly one outcome (same outcome for everyone) Biological systems are probabilistic, hence much harder to calculate. In real population, we tend to use probabilistic instead of deterministic factors since it is more 'real' Population projection matrices: We can think about population growth in terms of matrix algebra. For each individual at a given age, there is a probability that you survive to the next age (P :xProbability x --> x+1). Likewise, you have a frequency of reproduction that is probabilistic that is age dependent. The number of offspring born from age x moving to the next age (F : Nxmber of female offspring born x --> x+1) You built a transition matrix to help answer how we deal with demography. To calculate N (t+1)you use population vector multiplied by transition matrix BIOL215 Lecture 15 Notes λ equals to N (t+1)N(t)d is the geometric rate of increase. It can only be used with geometric models unlike r, which can be used with various other models Stochastic models that is integrating probabilistic viewpoints when we are looking at population growth since probabilistic is much closer to reality Two main parts on a Leslie or transition matrix: fecundity and survivorship Examine Table 10.2 to see the difference between r and k-selected life history. Understand the differences between the two different type of life histories In turtle experiment, researchers found that large juveniles had the greatest impact on population because of its survivorship. If researchers focused on fecundity, there won't be a positive impact on growth of population Two main forms of competitive interactions: • Among individuals within population: intraspecific competition • Among individuals from different species that are using the same resource: interspecific competition Logistic population growth assumes that growth slows and stops as resources become limiting We assume that at carrying capacity, when population stabilizes, resources are the limiting factor and stops population growth Competition and niches of small rodents experiment by James Brown: The hypothesis was that if competition among rodents is mainly for food, then: Small granivorous rodent population would increase in response to removal of larger granivorous rodents • Insectivorous rodents would show little or no response • The results supported the hypothesis To cap: BIOL215 Lecture 16 Notes In general, Lotka and Volerra predicts coexistence of two species when, for both species, interspecific competition is weaker than intraspecific competition Lotka-Voltera provided a mathematical model based on the logistic equation: • Logistic equations for species 1 and 2: • Intraspecific (within species) competition is represented by K-N/K The assumption is that resources diminish as N increases because of intraspecific competition Obviously resources will also decrease with interspecific (between species) competition. Lotka-Voltera proposed: Where a (alpha) and b (beta) are competition coefficients Populations will stop growing when: • As summary: N wil1 fill the space when N = K a1d N 1ill fil2 the space when N = K /a 2 1 • The line of "Zero isocline" which is the limit to the growth of the population of species 1 that is imposed by the number of individuals of species 2 • Competition can lead to one species winning and the second species going extinct Some competition interactions can lead to coexistence We can understand competitive interactions only by knowing the resources involved and the mechanisms by which species compete The outcome of competition will depend on environmental factor In the Galapagos finches, there's been an avoidance of competition to a large extent by evolving characters that have displaced food competition. So it was competition that has driven evolution Plant ecologists proposed a triangle. Phil Grind says that in plants, it's not K or r that allows you to understand the different types of plants, but that a plant will respond to three different axis based on the triangle: importance of competition, importance of stress (temperature, draught, cold - gradual change in environment), importance of disturbance (fire, hurricane, tsunami - more local scale and is not something that is continuous). Competition is one of the three most important axis that will explain species cohabitation Predation Predation is different from competition because in competition, we have two species and their relationship is mediated by abiotic resources. In predation, the relationship between the two species is direct, one species is a source of food for the other species Predator kills and consumes its prey. Dynamics of predator prey populations: Population cycles of predators and prey are well documented for a wide variety of animals living at high latitudes: lemmings, voles, muskrats, red fox, Arctic fox, ruffed grouse and porcupines The predator-prey hypothesis: Predator density increases in response to increase in prey density High predator density in turn reduces prey density Population cycle exists because of the overpopulation hypothesis: • High population growth is followed by decimation due to diseases and parasitism • Physiological stress at high density leads to increase mortality • Starvation due to reduction of quality and quantity of food The mathematical model: let us assume that the host population grows at an exponential rate: Limit to host population growth due to predation. Limit imposed by predation will be a function of predation rate (p), host population size N(h), and predator population size N(p) • For the predator, Lotka-Voltera proposed that: • where c is a conversion factor, the rate at which hosts are converted into predator offspring and d(p) is the death rate of the predator • There are two theoretical possibilities for isoclines for predator growth. Assuming single predator-single prey system You need to have a certain number of preys before you can sustain a population of predator. Once you have prey, predator will increase, hence a straight line up. That would be zero isocline The other theory is that predator will not constantly increase because something will happen (i.e. disease, harder to hunt prey due to low population), thus not a perfect linear increase and an isocline that is more curve See page 193-194 in textbook (not on final exam) • Refuge: How can a prey escape predation? Refuges as situations in which members of a population are protected from predators and parasites • Space: The first form of refuge that one envisions is space: burrows, trees, etc. Number: Population size might provide a refuge. Living in large groups can intimidate predators while it reduces the probability of any given individual being eaten Size: If large individuals are ignored by predators, then size is a refuge Chemical or morphological defenses: Defenses can be divided into constitutive defenses (always present and continuously produced) and induced defenses (produced in response) Chemical defense are chemical produced by a prey to deter the predator Morphological defense are traits grown by the prey to deter predators eating it (i.e. cactus don't have many preys which can eat through its spikes) Another defense is called "Batesian" mimics (i.e. snakes that look like coral snakes but are not actually venomous). Through evolution, by mimic of another species that has a dangerous trait, these species can avoid being food for predators To recap: BIOL215 Lecture 17 Notes Based on the Rosenzwieg-McArthur model, as you have more and more prey, there is stronger and stronger intraspecific competition, so to stabilize the population of prey, you need less predators which is why the curve goes down Mutualism interaction is when coexistence is beneficial to both species. For the grouper and small fish example, we are not saying that the relationship is an obligatory mutualism; both the small fish and grouper can live apart and do fine. However, they will do better when they are living together • Mycorrhizae as a mutualistic interaction. Mycorrhizae fungi provide plants with greater access to inorganic nutrients and are important to plant performance Herbivory interaction: Herbivore consumes its prey but does not always kill it. Herbivore is a mild form of predation Predation interaction: Predator kills and consumes its prey. The herbivore-plant relation is one of predation There is a high metabolic cost to defend oneself. The production of thorn takes energy, nutrients. Thus, the plant's fitness level overall will decrease. A good example of a plastic functional response in this case to herbivory suggests that herbivore will have a big impact on the growth of plants The hypothesis of overcompensation in plant responses comes from the idea that herbivores may not be all together so negative for plants. It suggests to a certain extent that as grazing pressure increases, it might even be beneficial and lead to an increase in production. This may be due to intraspecific and interspecific competition • Serengeti Plains is a good example of the herbivory interaction linked with the overcompensation in plant responses due to grazing (Zebra eat first, then wildebeest, then Thomson’s gazelle) • Parasitism interaction: Predators, parasites and pathogens influence the structure, abundance, and distribution of population. It is a form of predation. At times, it may lead to killing the prey, but this does not always happen • Parasite: An organism living in with or on another organism, obtaining benefit from it and usually injuring it (i.e. Lamprey) Parasitoid: An insect (wasp) that complete its larval-development within the body of another insect eventually killing it A number of parasites and pathogens will alter the behavior of the hosts to benefits their own life-cycle For simple models of population regulation, if the birth and death rate curves do not cross, the population will either increase to infinity or decrease to extinction Interspecific, intraspecific, and predation is basically density dependent. This suggests that death and birth rate may change as we change population Two general rules for simple models of population regulation: Population stop increasing if either birth or death are density dependent Differences between two populations in equilibrium density can be caused by differences in either density dependent or independent per capita death and birth rates When we are talking about population regulation, there are two types of factors: Limiting factors: factors affecting average of equilibrium density (i.e. diseases affecting deer population) - is factor that will affect population irrelevant of density Regulating factors: if percent mortality resulting increases with population density (i.e. diseases if more mortality when deer population is high) - density dependent, will not play when density is low, but will come to play when density is high Extrinsic regulating factors - predators, food supply, diseases, parasites, weather, shelter Intrinsic regulating factors (within population) - sex, age, physiology, behavior, genetics In density dependent systems, predation can be compensatory. This means that competition would limit the growth of a population so there can be predation in my population, and this predation will have no effect on my population because it is only taking out the individual which would have died anyway because of competition Predation may also be additive so there would be mortality due to competition in density dependent system • and predation is in addition to that. Thus, predation exerts an effect. So different systems will have predation as either additive or compensatory • Metapopulation: "A population of sub-populations" • A species whose range is composed of more or less geographically isolated patches, interconnected through pattern of gene flow, extinction and recolonization is said to form a metapopulation A group of 'source' and 'ink' sub-populations controlled by density dependent immigration A dynamic view of community on the landscape where you have source sub-populations (sends individuals outwards) and sink sub-populations (poor patches of habitat that can receive individual but will never send them back). Together, source and sink sub-populations maintain density at an optimal level for thriving conditions • The source populations are areas where local reproductive success is greater than local mortality (λ > 1)* • The sink populations are poor habitats where local productivity is lower than mortality (λ <1) • These areas would spiral to extinction without immigration from source populations It is believed that with 10% of source habitat anywhere for a population to be viable; allows metapopulation to maintain an optimal condition Following local extinction, if immigration replenishes the sink populations, one talks of rescue effect BIOL215 Lecture 18 Notes In food chain or food webs, the concept means transferring energy from plants to herbivores and carnivores Food chain is looking more at the linear connection between two species while food web is looking more at the big community and the multiple food chains within the food web When we talk about food chains, we use trophic levels (the positions in the food chain/food web) to describe who eats who In trophic levels, the position tells you the function of the individual in the food chain What is the limit to food chain complexity? As the richness of a community increases, the number of links in species tends to increase as well. Essentially, each species is connected to more and more species as diversity increases. In addition, chain length is the number of links running from the top predator to the basal species In general, at any trophic level, many more species interacting (not much longer food web). On average, in a food web, every species is linked to anywhere between 8-12 species, but the trophic chain levels is anywhere between 4-5 levels Two hypothesis to explain why food chains aren't longer: • The energetic hypothesis: Length is limited by inefficient transfer of energy The dynamic stability hypothesis: long food chain are not stable • For those in community ecology, it's important to understand that when looking at the community, we are expecting a relatively constant relative-prey and herbivore-plant ratio. It follows the transfer of energy concept where there has to be an equilibrium of predator-prey/herbivore-plant ratio Generalization (page 407-409): As diversity increases a species is connected to more and more species Food chains tend to be short • There is a constant proportions of top predator, intermediate species and basal species in a community at equilibrium • Keystone species: Is a species that plays a role in a structural role in a community that is completely disproportionate to its abundance. It is a species that ends up structuring the community due to its function, not because of its abundance • Paine's experiment demonstrated the effects of keystone species in the sense that the control (containing starfish) contained on average 15 species, while the starfish removal trials only contained 8 species with mussels dominating the majority of the species. The reason was because starfish mediating coexistence by preferentially feeding on mussels and barnacles There are various categories of keystone species: A major predator: (i.e. Pisaster ochraceus) which preys on the rocky intertidal zone of the North american pacific coast A unique food source: In central America, frugivores have to rely on a very limited number of tree species for food An ecosystem engineer: A species that maintains critical ecosystem processes (i.e. beavers & elephants) It is important to distinguish between dominant vs. keystone species. Keystone species have a huge impact on the community due to their function, but they might not be very common and lack abundance. On the other hand, we have species that are abundance and have relative little impact on the community Two views of community organization: In bottom-up model, nutrients control community organization by controlling plant numbers. Also known as donor-control Assumptions: Weaker interactions (decoupled) Lots of competition will structuring these forces and there were resources will be the limiting factor of growth In top-down model, predation is the structuring factor because predators control the number of herbivores. Also known as trophic cascade Assumptions: Strongly coupled interactions. Predators suppress herbivores and herbivores suppressed releasing plants to flourish For herbivores, the predation is the structuring force and predator is the limiting factor unlike bottom-up model An example of bottom-up or donor control interaction comes from wolves, and other predators who frequently consume weak moose individuals and so do not influence moose population growth much. This is called compensatory predation Trophic cascades also occur in terrestrial communities The special case of islands. Biogeography or geographic ecology: It is the study of historical changes in distribution pattern of animals and plants across the landscape over time and over space. It is an extension of community ecology and builds on it but it looks at a much broader spectrum of space and time Mathematics of species-area curve: Most prevalent mathematical form of relationship: • The relationship is linear on a log scale: • where S = number of species on island, A = island area, C = constant measuring the number of species per unit area and z = slope (average 0.3; range: 0.15-0.35) • can be used to estimate loss of species due to habitat loss Taking the immigration of new species and curve of species extinction rate, you can find the number of species on the island by finding the equilibrium (the point where the two curve crosses) of number of species BIOL215 Lecture 19 Notes Hyperparasite: Is a parasite of a parasite, often Hymenoptera. It is mainly found in the world of insect Primary succession describes the growth of plants on a substrate that is rock (not living, and never experienced a growth of a community before - i.e. Mt. St. Helene) In the case of Lupinus present on Mt. St. Helene, there were two processes: • Chance event (probability) that seeds come in via birds or wind • Effect of Lupinus as a species that facilitates or helps colonization for other species During primary succession, facilitation is one process where facilitating species modify the environment to make it less suitable for them more suitable for others (i.e. Alder trees fix nitrogen in soils) Another model of succession of how plants change over the course of time is inhibition (i.e. Abandoned tobacco fields in the Piedmont of North Caroline) The example of Broomsedge is a good example of inhibition model. Broomsedge inhibits establishment of aster by scavenging water and nutrients from soil near parent stems. Inhibition is the reverse of facilitation, instead of improving the soil for other species, inhibition species would take up all the resources in that site and exclude other species In all three model of succession, there is an element of chance and an element of what is the constitution of the communities around the place where succession is taking place that will determine which of those pathways will take place • Colonization process, movement to newly created volcanic islands is well documented (primary succession): • Krakatoa in Java Straight • Surtsey near Iceland Mt. St. Helene Indiana sand dunes (primary succession) example Secondary succession: A change in the habitat but a habitat that was already sustaining a biotic community (already a biological substrate) - i.e. Beaver dam forms pond Secondary succession can occur in other conditions. Inhibition is an example of secondary succession. Other examples include cutting down forests, changing wetlands Table 18.1 on physiological and life history characteristics of early and late-successional plants is tied into earlier lectures on the k and r selection in addition to Grim Triangle (stress tolerant, competition, and importance of disturbance) The old view: Climax as the end point of succession is the climax Climax: the final or stable community in a successional series. It is self-perpetuating and in equilibrium with the physical and biotic environment There are three main different views on climax: Monoclimax (original proposal): In any place in the world, there is just one type of community that can live there; as a function of climate Polyclimax: Depending on the physical environment (geographic condition, soil moisture, nutrients, rocks, etc.), you would have different communities Climax-pattern: Responding to a range of ecological factors and with more than one climax type in a region; pattern of changes, seeing climax as quite mobile equilibrium with many species taking over the community depending on precise and specific conditions that have to do with geographic and climate (precipitation) Climax is rarely a deterministic, fixed endpoint of succession, but rather a continuum of endpoints, depending on soil conditions, among others The classical paradigm in ecology views ecosystem as stable • The new paradigm views ecosystem as open and in non-equilibrium. Metler's wood (oaks) is an example • Different communities can reach different equilibrium based on what is happening • In intertidal communities, different succession occurs depending on clearing size. The size of the clearing will send the system to one of two different community, a two-stage community Another example of two-state system occurs in Australia: grazing effect from herbivory or fire will create two different community For non-equilibrium communities, communities may not be in equilibrium if they recover from disturbance • Non-equilibrium community are understood as being dependent on disturbance. This is important for management and for understanding ecology • Two main characteristics of disturbance: • Frequency: how frequent are disturbance. If a system depends on forest fires, how often are there forest fires Intensity: physical force of the event per area per time. How strong is the forest fire? Severity: effect on the community. If the severity is great, it will set back the community earlier in succession than if the severity is milder Stability is composed of resilience, resistance, and persistence: • Resilience: the degree to which a system returns to its original state after a disturbance has passed and the rate at which it does so • Resistance: the degree to which a system is altered as a result of a disturbance Persistence: the time it takes before the system shows perturbation (modification) Diversity is maintained through the intermediate disturbance hypothesis which suggests that when disturbance of a medium intensity and frequency, they foster a maximum diversity in any system. This is because if we have little or infrequent disturbance, very few species would have the competitive ability to maintain themselves in the system. If we have very frequent or very intense disturbance, very few species will be able to maintain and cope with the intensity in the system Diversity is higher in the southern latitude and diversity tends to be lower at higher latitudes Three constituents which explain rarity (7 possible forms of rarity): Geographical distribution Population size Habitat specificity Biodiversity hotspot: It is a geographical area on the globe where we have a disproportionate number of species; where we have species that are very abundant • Endemic species: Characterized by a very restricted geographic area; they are found in only one place and thus are very vulnerable • Umbrella species: A specie that you can focus on conserving, and in doing so, you would conserve a whole range of other species • Species' abundance are log series. In communities, you tend to see many rare species and few common species, this tends to be the pattern of distribution • Communities are structured by chance (says Steve Hubble); whoever comes in, gets in there and whoever gets in there, takes the resources and grow - The neutral theory In the old community ecology, we've been looking at succession and saying it's stable and will get to a predictable equilibrium. The species will come in based on their characteristics which will determine the niche and will make the community happy (very predictable) The new community ecology disproves the old community ecology. It says community will have multiple end point of succession, multiple states. These multiple states will depend on various factors such as disturbance and the composition of species which is described by chance alone with niches explaining very little of why species cohabit together Another theory (equilibrium island theory of biogeography) explains the species' diversity on islands where we only have to invoke distance of dispersal and the size of the island. Nowhere on the model did we have to explain the niche or use the niche to explain. We only state that if an island is far from mainland, you will receive less immigrant and if it’s a big island, you have less extinction Read page 387-397 BIOL215 Lecture 20 Notes Review: Population: a group of individuals from one species that occupy the same space at the same time In population biology, population will grow as a function of birth and immigration while population will decrease as a function of death and emigration A variety of equations that allow you to move from move the size of a population at time t to the size of a population at t+1 What is survivorship and reproduction? Examine different types of species with different survivorship patterns (Type 1, 2, 3). Different ways of summarizing the population vital statistics which are survivorship and reproduction Distinction between cohort table (all the individuals born at the same time and follow them through time) and static table (going into a population at one time and trying to understand the birth and death of that population based on what you see at that one moment) Equations for net reproductive rate, generation time, instantaneous rate of increase, and geometric growth Understand the impact of net reproductive rate on the growth of a population will depend on the generation time (the time it takes between two generations). Those two equations allow us to calculate the instantaneous rate of increase in a population Geometric growth and exponential growth has the same curve shape, but in geometric growth, you have discrete episode of reproduction like in annual plants, they reproduce in one year, everyone dies and then the next year, a new generation is born. In exponential growth, it is continuous reproduction but that yields the same sort of growth form The prairie chicken is a good example of a declining population One of the most important reasons why we looked at applications of demography is because it is important in conservation and allows us to make diagnostic about populations that are declining and to help us better manage those populations For geometric/exponential growth, it will apply to populations that will keep growing and growing without stopping In realistic terms, populations will follow the logistic growth where the size of a population will reach a plateau where it reaches a carrying capacity (the moment where the population stops growing) Growth: the change of individual over time Population size: the number of individual at a given time Carrying capacity: the number of individual where the environment cannot sustain anymore individual At carrying capacity, the population number stops, population number stabilizes, and growth stops. Population growth rate is maximum when the size of population is equal to carrying capacity divided by two. This application has been used to manage fishery and the challenges associated with the fishing industry From deterministic to probabilistic models. The models studied so far are predicting one exact outcome. Biological systems are probabilistic Species interaction competition - the interaction between different species. This is the realm of community ecology. Community: looks at many species that cohabit in the same space at the same time Intraspecific competition - why do species keep growing if we're looking population under logistic equation? It is because individual of the same species are fighting for the same resources Interspecific competition: competition between two different species fighting for resources In competition, we examined different ways of avoiding competition. Example is wobbler that forage in different places in different trees. We also looked at the fact that competition is a structuring factor in competition A second type of interaction between species is predation. Understand coupled models of predator-prey and the cycling of the model (abundance of prey controls abundance of predators) To cope with predation, we know species take refuge via shelters, numbers, size, aposematic coloration such as the "Batesian" mimics in snakes Different types of interactions such as mutualism, parasitism, and herbivory and make relationship between these and earlier interactions Understand density-dependence: the more abundant the individual, the stronger the interaction between individuals. Density-dependence is something that plays in population, that will regulate population. Logistic growth is an example of density-dependence Population number can be predicted depending on the density-dependence or independence of birth and death rate Metapopulation: instead of looking at a population as a single group of organisms that occupies a single space, we know conceive a population as a group of individual but that is using scattered space, space that is fragmented where some part of the metapopulation are linked to other subpopulation through immigration and emigration. That entire understanding of metapopulation builds on density-dependence because as density becomes high in source population, the source population will foster emigration to other subpopulations around to regulate its density Understand food chain as a direct link of who eats who and the various trophic levels where energy moves up the food chain Use food chain or food web to reproduce the interactions of different species in a broad community. Keystone species plays a crucial role in a community through its structuring properties. Removing keystone species will result in extinction of species in the community Dominant species play a vital role due to their abundance and biomass in the community Understand bottom-up and top-down trophic level • Bottom-up trophic level: production of herbaceous system is controlling the system. The case of the plains in the Serengeti is an example of bottom-up trophic level where grass production determines the presence of herbivores and the lions will only kill weakened herbivores due to compensatory predation • Top-down trophic level: where the system is controlled by the predator. The classic example is the cougar -- > hare --> grass In island biogeography, we saw that using log scales, there is a positive relationship between area and number species. As you increase the area of the island, there is an increase of species. The other model looks at the equilibrium model of biogeography. It predicts the equilibrium number of species as a function of immigration and extinction on islands. If an island is large, it will have lower extinction (island is small will have greater extinction), and if you are far from the mainland, you will receive less immigration from the mainland (and vice- versa). Using the intersection of these curves, using the immigration and emigration curves, you can determine the number of species present on the island Changes in community and changes in time through succession. There are three models of succession: facilitation, tolerance, and inhibition In facilitation and inhibition model, the first species that comes in will modify the environment in such a way that it will either exclude itself and helps others come in or improve the environment by excluding itself and facilitate others to come For tolerance model, the first species that comes in will modify the environment in such a way that it will exclude the others and dominate • There is always a chance event in succession at the beginning of succession of which species go in first and thus, have an impact on how the system will evolve • Two views of community. The old view of community is known as “climax communities” which evolves to a known equilibrium and once they've reached this equilibrium, they will maintain themselves in that equilibrium. The new view of communities is that communities can have different states and does not have to reach the same equilibrium after a disturbance • Disturbance becomes a key factor in understanding community. Understand the importance of frequency, intensity, and severity of disturbance A maximum of diversity is fostered by a medium intensity and freque
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