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2011-11-29-Chapter 20-24 Recapture.docx

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Biology 1002B
Philip Egberts

Biology Recapture (Lecture 20-24) Lecture 20 – Population Ecology Sections 45.3-45.5 Virulence and Transmission Remember, a parasite does not want to fully kill the host. The host individual needs to be kept alive so that they can further infect others (new hosts). This is known as the trade-off hypothesis. There is a particular version of this trade-off hypothesis and is known as the Transmission mode hypothesis. It states that there is an optimal virulence of a parasite and is dependent on the how the parasite actually moves between the hosts. Some virulence requires direct contact, whereas some other individuals do not require direct contact. Some parasites can be spread through indirect means. An example of this is the transmission of contaminated water, and other hosts such as bugs. Pathogens can be released from inanimate objects as well. This is seen in public places such as washrooms or hospitals. Parasites that can be spread through indirect forms tend to have a more virulent effect. Many direct transmission methods are less effective or virulent. There is a lot of evidence supporting the Transmission mode hypothesis which is the reasoning for its great acceptance biologically. There are practical implications of this method of transmission then just defining the principles. By understanding these concepts, we can determine the ways in which virulent diseases will evolve over time. From a physical perspective, if we reduce chances for indirect transmission (i.e. Water supplies), parasites will rely more on the direct transmission methods, which eventually promote evolution to reduce the virulence. Overall, this will reduce the fitness of the individual parasite, but will be more beneficial to humans. Population Ecology A population is a group of individuals of the same species that live in a defined geographical area. Although this is an arbitrary definition, there is a common acceptance of what the location may be. Any location is a viable explanation of location. We will be looking at a variety of scales. Characteristics of Populations Populations have many attributes that are not associated with the individuals. They consist of: - Allele Frequencies, genotype frequencies - Population size(N) - Geographical Range - Sex Ratio – Males to Female - Age Structure – Sexual Maturity or Not? - Rate of Growth Estimation of Population Size In the human population, we have a constant total of individuals that will be extrapolated to help us determine the population. If you are dealing with organisms that do not move, you can simply count all the individuals in a said location to get the population and rate of dispersion. If the organisms move however, there is the need for additions counting systems. Methods of Estimation There are multiple ways to estimate population size when we do not have access to all individuals conclusively. The Mark Recapture method is the most common method of tracking individuals. You go out into the field, catch a bunch of individuals, and place a marking on them. At some point in the future, you come back and capture a bunch of individuals. This new set of individuals are inspected for the number of individuals that were recaptured (had already been marked). We can then calculate the number of recaptures, which will allow us to measure the total population size. Mark Recapture Method R/C = M/N, Where R is the Recaptures, C is the number captured in the second visit, M is the number of Marked individuals. We then isolate for N, which is the number of individuals in the whole population. We clip the toes of 100 frogs in a lake. You then return and Capture 75 Frogs, that of which have 10 clipped toes. How many individuals are there in the lake? There are 750 individuals. Mark recapture method works well only if the marked and unmarked animals are equally likely to be captured. If an animal is marked, it should not be more likely to be found the second visit. Also, the marks on the population must not affect the survival of the individuals and the marks cannot wear off. This means that although the marks may come off in a few years’ time. As long as the marks are still present during the second capture, the method will work well. The time between the first and second visit should be fairly close together to avoid Births, Deaths, Immigration and Emigration. In a mark-recapture study of blackbird, many individuals became trap happy, where after they are caught a first time, they are very easily caught again. How will this affect the estimation of population size? This will cause us to under estimate the true value for population size. If you were to use washable mark to mark the wings of butterflies in a mark recapture study. Some marks wash off before the second sample is captured. How will this affect your estimate of N? This will cause an underestimation of recapture and an over estimation of the total population size. Population Density Sometimes we are not as interested in the number of individuals in a population, but rather the dispersion with respect to area. There is typically an inversely proportional relation of body size to density of individuals. If there are very small individuals, there will be greater density. Why does density matter? Density influences the overall access to resources. If the density is too high, the per capita growth rate may decrease. The denser a population is, the smaller the rate of growth is. Remember, there are both Density Dependant, and Density Independent factors that will play a role. If the density is too low, per the per capita growth rate may decrease. This is known as the Allee effect. If individuals struggle to find a mate because there are so few individuals, they will have a decrease in growth. If individual hunts in a pack, their performance and success might also drop. Population Dispersion With a specific density, there are three types of dispersions that actually occur. Most populations have the clumped method of organization. The three types are: 1. Clumped 2. Random 3. Uniform We see that if there is a food source in a specific location, the population will be clumped towards that location. Uniform dispersion is found mostly in the plant population, or animals that have very similar competition over the land mass. There is no need to have competition if there are many resources available. Dispersions can change overtime. In the breeding season of birds, there will be the uniform dispersion patter, but in the winter time, there will be the formation of flocks, which represents the clumped dispersion. What are some advantages of living in a group or clumped dispersion? - Protection - Raising Offspring - Cooperative Hunting - Ease of Finding Mates What are some disadvantages of living in a group or clumped dispersion? - Competition for Resources - Disease Control Characteristics of Populations That Affect Population Growth Rates Which population would grow fastest? A population with more females than males will be most successful. Feamles are a limiting resource in a population. In all different situations, there may be the need to have a variety of combinations with respect to male to female ratio. In most populations, females are the limiting factor, but this is not always the case. Generation Time The faster the generation time, the faster the population will be able to grow. Imagine that there are two populations, both with an average of offspring produced per female per lifetime, and only differ in their generation time. Population 1 reproduces at age 16, and Population 2 reproduces at age 32. The population that reproduces at age 16 will continuously have many more offspring produced over the time. Increasing the generation time very quickly decreases the overall population number. Education of females is the best way to increase generation time and decreasing population growth. Lecture 21 – Population Ecology Read Section 46.1, 46.4 There are final Exam notes posted in the Test Resources Folder. Population Ecology Consists of: 1. Age structure and population growth 2. Life tables and survivorship curves 3. Life history strategies 4. Models of population growth Population Growth Rate Age structure encompasses the ages of individuals in a population that are able to reproduce. Many age structure pyramids or histograms can explain if a population will grow fast, slow, or not at all. When the young individuals are in abundance, the population will experience rapid growth. This is the most desirable conditions that could occur. Negative Growth occurs when there are very few pre-reproductive individuals, while there is an abundance of post-reproductive individuals Life Table Analysis A life table analysis summarizes survival and reproduction for a cohort of individuals. A cohort is a set of individuals that are very similar in age. (I.e. a school year or so). We should be able to fully follow a cohort through the development. This data can be collected and placed into a life table. It classifies the cohorts based on their age, and what ranges they fall in. The measurement is based around how long each individual species lives. Does the species live to the next generation of species? We can use this data to calculate age specific mortality rate (death). We can also calculate the survivorship of each age period. Survivorship Curves Survivorship curves are no really based around number of individuals or when they are born. A survivorship curve is based around the period of time when many individuals go through mortality. Large animals tend to go through the type 1 survivorship curve; there is very little chance or mortality until the species becomes very old. There is very little juvenile mortality. Smaller individuals tend to follow the type 2 survivorship curve. In this type, most individuals are not dying because of old age, but rather environmental factors. All of these factors are unrelated to the age of the individual. There are some organisms that will actually follow the type 3 survivorship curve. In this case, most mortality occurs in the early years of individuals. Very few individuals make it past the first bit of life. Once they make it through the system, the majority of the lifespan is constant. Life History Characteristics Life history is the study of how organisms allocate energy and resources given the fact that they have many competing demands in their live. All creatures must partition energy and resources all the time. Demands consist of: - Growth - Reproduction - Self-Maintenance(repair) Each of these is examples of components that must be balanced as a category, and also in a sub- categorical way. Each individual will have a different life history strategy, which is a denotation of how resources will be allocated over the lifespan to themselves and offspring. Different environments place various stresses on the delegation of resources due to the specific needs. Quantity and Quality(R strategist and K Strategists) All individuals fall somewhere between r selected species and K selected species. When individuals reproduce very early in their lives, they are most likely an ‘r’ strategy type system. These species tend to invest very little in the offspring. K species are very different compared to R species. They tend to devote lots of energy to growth, self-maintenance and repair. The time required to reproduce in K species takes long, but the average life if much longer. There is a lot more parental investment, which leads to lower juvenile mortality. R species are producing high quantity of offspring, while K species produce high quality offspring. Population Growth Predictions To calculate growth of a system, we must integrate all of the factors (Births, Immigration, Deaths, and Emigration). The equation includes the summation of Mortality components, and then the subtraction of the natality components. (B+I) – (D+E) = Growth rate. This equation is modelled over time, and the Growth rate is model in terms of change in population before (currently) and after (future). Per Capita Birth and Death Rates per capita are extremely useful. There is a system where there are no immigrants or emigrants. We will to calculate the birth rate per capita. This is modelled as B/N. This is the same for the death rate, and is modeled by d=D/N. Rate of Growth Once we know the per capita death and growth rate, we can calculate the intrinsic growth rate = r. r=b-d. In the exponential model of growth, r is independent of the total population size. The rate of change in the growth of a population is the intrinsic growth rate(r) multiplied by the total population, yielding (rN). Exponential Growth In exponential growth, we see that the overall population will increase in size if R is greater than 0. If the R value is less than zero, then the total population will decrease. The doubling time of the population can be found by taking 70 and dividing it by the r value as a percentage. Remember, this all works in theory, but it is often unrealistic to assume that growth is independent of the N value. Logistic Population Growth For any population, in any given environment, there may be a maximum number of individuals that the environment can sustain. This is known as the carrying capacity value and = K. As N increases, the rate of growth will decrease. (K-N)/K is the growing room that the system has. This is an extremely important value, as it measures how much room for growth in this system is possible. The rate at which a population will growth in a logistic model is represented by: rN ((K-N)/K) The only difference between an exponential growth curve and a logistical growth curve is the factor of resources. If resources are limited, there is the development of a carrying capacity, which leads to the logistical growth pattern. If the resources are completely abundant, then the exponential growth pattern will happen. If there are 900 individuals in a population, and the carrying capacity is 1000, along with a r value of 0.1 ,then after one year, the population will grow to 0.1 x 900 x (1000-900)/1000 = 9 individuals per year. If there is no carrying capacity, the growth would simply be 0.1 x 900, which would be 900+90 after 1 year, leading to a net value of 990. When N= K, the carrying capacity has been hit theoretically. In an exponential growing population, the r value will maintain the same value over time, but in the case of a logistical curve, the r value will decrease as the system reaches the carrying capacity. When N is very small, the R value is extremely high. If there is a group of salmon that could have a maximum population size of 500 individuals, what population size at the time would have the most aggressive (greatest) growth rate? Logistical Model Misleading When N is 0.5K, the growth rate is maximized, as this is the derivative of the curve. In theory however, not everything that grows logistically will follow the pattern and rules 100%. The Allee effect will cause the population to die out if they fall below some minimal density in a location. There is also the potential of a time lag where the population may overshoot K and then dip below K. Density Dependant Factors - Starvation - Disease - Competition - Predation - Emigration - Parasitism - Accumulation of wastes Density Independent Factors - Act Regardless of the population size - Disasters - Server Weather - Fires - Floods There is the possibility for both density dependant and density independent factors can interact with each other at times which may drive the said population right into the ground. In Haiti, we saw the blending of both of these factors. The DIF was the earthquake that wiped out part of the population, while the DDF was the access to food and other sicknesses that occurred later. Human Population Growth Most K-selected species show logistic growth, but what about humans? Humans have been exhibiting exponential growth over the last thousands of years. Why is this the case though? Lecture 22 – Community Ecology 1 Why is it that humans do not follow the rules of logistic specific growth? Humans are still under their carrying capacity significantly, which allows for lots of expansion. We also have technology present, unlike most species, which allows for us to continually adapt to the situation. We also have access to resources that we can manipulate in any way we wish, unlike other animals. We also have no other predators at the time which reduces the competition for most consumer based goods. Why is the human population still growing? There is in fact, no specific reasoning, but we have utilized the equated based representation of the population to a point where we have been able to increase the carrying capacity overall. We have improved all aspects of the N value in our population. We have increased carrying capacity, reduced death rates, and increased birth rates. We have also made adjustments so that we can increase our performance. Variation in R. We have projected population sizes for future years, and we see very little trend. However, we see that Europe will most likely decrease while Asia increased. From the standpoint of North America, it appears as though we will make no significant change. Reflection R reflects the overall age structure of a geographical region. In the case of the USA, we see that there are many individuals that are pre-reproductive and reproductive. In the case of Mexico however, we see that there are just many pre-reproductive individuals. Increasing N, but Decreasing r Globally, we are increase at about 1.2% annually, per person per year. Our r value is overall decreasing, but our N value is still increase with great demand. In the last few years, we have been significantly increasing our value of N, which is shown by the 7 billionth person in existence. Remember that r represents the slope of the population. So although we are increasing overtime, the rate at which we are increasing is become lesser. Transitional Model Over time, human societies have become more advanced, and wealthier overall. Birthrates have been decreasing overall, while death rates are decreasing. In the case of some third world countries, the birth and death rates are extremely high, which leads to a balance, and an extremely low value of R. When these populations increase in success, they move towards cities, which allows for improvement in concepts that prevent as many death rates. As medical conditions improve worldwide, the numbers of death rates decrease greatly. At this point in time, there is a large change in r value positively. The post- industrial stage is when there is zero population group (when birth and death rates are equivalent, disregarding immigration and emigration). Modelling Most of these models apply strictly to first world countries that are extremely bias and advanced. This may suggest that the models will not accurately predict systems in third world countries. Population Size isn’t Everything These models explain that most populations will decrease in size, as they will mostly be entering the post-industrialized situations. In terms of population, size may not be everything. The resource use per person may be a much more important factor than that of the actual growth. North American resource use is approximately 50 times larger than that of thirds world countries. This lead sus to have a much great ecological and carbon based footprint. Community Ecology A community is a set of populations that interact with each other. Population ecology looks at one species at a time, and the said interactions, whereas the community involvement looks at multiple locations a
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