Ecology Exam 2 Chapters 11,12, 22 Flashcards
Compare and contrast the geometric growth model and the exponential growth model.
Blot: A model of population growth that compares population sizes at regular time intervals: geometric growth model. Example california quails only reproducing thru out one breeding period and no new babies after that. Exponential we know intrinsic growth rate (The highest possible per capita growth rate for a population) and based on that can tell how a population will grow over time under ideal conditions. Humans exponential growth.
Exponential growth model is used when we know the intrinsic growth rate for a population and we want to estimate how a population will grow over time under ideal conditions. Populations with higher intrinsic growth rates or a larger number of reproductive individuals will experience a greater rate of increase in population size. The exponential growth model applies to species, such as humans, that reproduce throughout the year. However, the geometric growth model is used for species like quail that have a distinct breeding period. This is because it compares population sizes at regular time intervals. In the case of the California quail, for instance, the geometric growth model allows us to compare population sizes at yearly intervals. They are both models of population growth.
Given the relationship between λ and r in the geometric and exponential growth equations, can you demonstrate mathematically why λ must be 1 when r is 0? Explain.
Blot: if lamda bigger than 1 that means population increased from one population to the next. MORE BIRTHS than deaths. IF less than 1, more deaths than births. Constant population lamda equals 1 and r is 0.
When population is constant, λ is equal to 1 and r is 0. This is because a λ larger than 1 would mean population has increased from 1 year to the next due to more birthdays than deaths. When λ is less than 1, population size has decreased and because off more deaths than births.
Given that white-tailed deer give birth to fawns each spring, which population growth model would be the most appropriate and why?
A geometric growth model would be most appropriate because it would able to assess the population size of white-tailed deer during the spring, its distinct breeding period. This is because the deer population experiences a large boost in its population size in the spring due to reproduction, but then the population slowly declines over the summer, fall, and winter due to deaths and no reproduction.
Contrast the concepts of a stable population versus a stable age distribution.
Blot: When the proportion of individuals in each age class does not change over time, we say it has a stable age distribution. If same # of species from like 0 to 50 years, stable population.
When the proportion of individuals in each class stay constant over time, the proportion λ in each age class does not change over time, it has a stable age distribution. If same # of species from like 0 to50 years, stable population.
In a life table, what is the fundamental difference between survival rate and survivorship in words and in terms of calculations?
Survivorship refers to the fraction of individuals that lives up to a certain age (versus survival rate, which is the probability of an individual surviving a given unit of time. While Survivorship is the observed survival, the survival rate is the expected survival. You could be talking about the survival rate from years 2-7, or the rate from years 3-4, but when you’re talking about survivorship you’re always talking about a survival rate starting at year 0 and ending at the year in question.Survivorship is not measured at the beginning of the organism’s life. Survivorship is a measure of how much of the initial population from time 0 has survived to time X.
Survival rate is how many offspring have survived each year. The probability of surviving from birth to any later age class, which we call survivorship. Survivorship in the first age class is always set at 1 because all individuals in the population are initially alive. Survivorship at any given age class is the product of the prior year’s survivorship and the prior year’s survival rate.
What is the relationship between generation time and the rate of population growth?
Blot: shorter generation time = quicker population growth. Ex Ecoli has 20 min gen time so 3 gen in one hour, sterptococcus has 30 min gen time so 2 gen in one hour
The generation time (T) of a population is the average time between the birth of an individual and the birth of its offspring. The shorter the generation time, the higher the intrinsic rate of population growth. The rate at which a population can change increases with shorter generation time, so indirect relationship. For example, E.coli has a generation time of 20 minutes. That means in one hour(that is 60 minutes) 3 generations of bacteria can grow. While in case of Streptococcus lactis(present in milk) generation time is 30 minutes that means it will complete only two generations in one hour.
Therefore, in the similar time period(that is one hour) , E.coli is growing faster with less generation time(that is 20 minutes) and S.lactis is growing slower with more generation time(that is 30 minutes).
When using the logistic population growth model, what are the different causes of slow population growth at low population sizes versus high population sizes?
Blot: The low population will initally increase quick til it reaches half the carrying capacity when rate of increase begins to slow because the reproductive individuals are each obtaining fewer resources. For high population sizes, it is reaching the carrying capacity so less survival cuz per capita resources become limited. Example 1000 wolves and 900 food pieces, only the best of the best can go on to spread offspring.
As the population increases from a very small size, the rate of increase grows because the number of reproductive individuals increases. After reaching one-half of the carrying capacity, which corresponds to the inflection point of the S-shaped curve, the rate of increase begins to slow because the reproductive individuals are each obtaining fewer resources. As it reaches carrying capacity at high population sizes, the population growth slows down because per capita resources become limited.
Imagine that you examined a large number of similar species that differed in how much each species stored energy. What would be the likely relationship between the amount of stored energy and the likelihood of the species’ population growth to exhibit delayed density dependence?
Blot: MORE STORE ENERGY REDUCES LIKELIHOOD OF POPULATION EXHIBITING DELAY DENSITY DEPENDANCE. when stored energy increases, population can survive above carrying capacity. they can migrate better, find more food, reproduce more so it reduces the likelihood of exhibiting delayed density dependance.
As stored energy in a species increase, it allows the population to survive above the carrying capacity. More energy stored, more ability to succeed adverse conditions by either migrating, finding alternate shelter or reproducing more, so this reduces likelihood of exhibiting delayed density dependence. This is because even if food is abundant in the fall and the carrying capacity is high, but by the time the offspring are born in the spring, the carrying capacity of the habitat may be much lower, the extra stored energy will help the population overcome lower carrying capacity.
Using your knowledge of small island populations and the importance of the rescue effect, explain the likelihood of extinction of the wolves on Isle Royale?
Blot: wolves will become extinct because isle is surrounded by water so no way new wolves can come. Rescue effect will allow introduction of more wolves to the Isle to save population.
If we let nature take its cause then the wolves will become extinct. This is because the Isle is surrounded by water so disperses cannot supplement the wolf population unless the water freezes over which is less likely to happen because of global warming. The island is too isolated so the wolves will become extinct in a matter of time. However if humans introduce wolves into the isle then we are introducing disperses ourselves and supplementing the population so we could save them from extinction that way
When predator and prey populations cycle, what are the likely causes of the cycling for the prey versus the predator?
Blot: there is cyclic population fluctuations and this is because if the prey species rapidly multiplies, the number of predators increases – until the predators eventually eat so many prey that the prey population dwindles again. Lack of food resources in turn decrease predator abundance, and the lack of predation pressure allows prey populations to rebound.
Cyclic population fluctuations in prey and predator are dependent on each other’s availability. When the size of the prey population decreases due to predation, the prey population responds by growing. If growth is rapid, prey populations can grow beyond carrying capacity. When prey population is high, predator population increases due to more food availability and can reproduce more. As the predator population grows, there suddenly becomes less prey available for everyone, so they reproduce less next season and their population decreases. Thus, predator and prey populations cycle through time, as predators decrease numbers of prey. Lack of food resources in turn decrease predator abundance, and the lack of predation pressure allows prey populations to rebound.
What are the differences between demographic stochasticity and environmental stochasticity?
Blot: both monitor population. Demographic has to do with when random variation in birth rates and death rates is due to differences among individuals and not due to environmental changes. Environmental has to do with environment changes that effect growth rate. Example of demographic stochasticity is due to fertility level, while example of environmental stochasticity is due to changes in weather ex too cold to breed.
Demographic stochasticity is when random variation in birth rates and death rates is due to differences among individuals and not due to environmental changes. This alteration of birth and death rates during sampling occurs independent of mortality and reproduction of individuals causing small random fluctuations. However, when random variation in birth rates and death rates is due to changes in environmental conditions its environmental stochasticity. It alters mortality and reproduction rates of all the individuals in the population similarly, causing severe random fluctuations in populations of all sizes. Example of demographic stochasticity is due to fertility level, while example of environmental stochasticity is due to changes in weather.
In a metapopulation of the collared lizards discussed in Chapter 10, how would decreasing the distance between habitat patches affect the synchrony of fluctuations among subpopulations?
Blot: decreasing distance will make dispersal more frequent. The individuals can travel from plot to plot so higher chance of colonization. When individual collared lizards frequently disperse among subpopulations, the whole population functions as a single structure and they all increase and decrease in abundance
Unoccupied patches that are close to occupied patches have a better chance of being colonized, and so dispersal is more frequent between nearby patches. When individual collared lizards frequently disperse among subpopulations, the whole population functions as a single structure and they all increase and decrease in abundance synchronously (sub populations fluctuate synchronously).
If you were trying to save an endangered species that lives in a metapopulation, how might you attempt to increase the proportion of occupied patches?
blot: Provide corridors so easier access to travel between patches, minimize deforestation in that area to protect habitat, make patches closer together.
Since the unoccupied patches can be colonised by dispersers from occupied patches, you can increase # of occupied patches by providing corridors (passageways) between neighboring populations, increasing the rate of colonization (like in collared lizards). A second way would be to decrease the rates of extinction by reducing the major causes of population decline in subpopulations (such as minizing deforestation). A third way would be lowering patch isolation and decreasing distance between the patches, since the closer the patches, less likely that endangered species will become extinct than between far patches.
In the basic model of metapopulation dynamics, how might the rescue effect alter both the probability of colonization and the probability of extinction?
Blot: Rescue effect is when individuals for another area arrive in a new area that was heading towards extinction. the rescue effect will increase the probability of colonization but decrease the probability of extinction. Extinction reduced cuz more individuals fill up patches. Colonization occurs to help declining population because species will go to zones they dont normally go
for me: The collection of subpopulations that live in isolated patches and are linked by dispersal is called a metapopulation
Migration of individuals to subpopulations to save the subpopulations with endangered species is the rescue effect. The rescue effect would increase the probability of colonization and lower probability of extinction. This is because rescue effect would increase # of disperser arrivals that supplement a declining subpopulation with endangered species. It would also increase probability that less small and isolated patches are occupied, reducing chances of extinction.
Why might different people or groups favor different criteria when prioritizing biodiversity hotspots?
Areas with low species richness can still have high conservation value. Just focusing on most species saved does not make it better, low species richness can have high conservation value. Saving ONE species may in fact have a positive effect on many.
By focusing efforts on the total number of species, they allow conservationists to avoid the hard science required to decide which species matter most to ecosystems and the hard choices required to decide which species matter most to us.
