Unit 3 : Reproduction/Population Growth Flashcards
(27 cards)
What is homeostasis?
Homeostasis is a process of negative feedback mechanisms used to maintain a factor within a given optimal range. It is using physiological and behavioural processes to maintain a relatively stable internal factor in the presence of changing external ones.
Example of the thermostat, how does it regulate temperature? What are the three parts of the thermostat that allows it to do this?
As temperatures increase, the thermostat acts to decrease temperature and vice versa.
Sensor / receptor: As temperature changes (stimulus), the thermometer within the thermostat will notice this, and send a signal to the integrator.
Integrator: Compares the changing temperature to a given set point, and if it differs from this is will send a signal to the effector.
Effector: The effector will then respond by turning off the furnace and turning on the AC or vice versa, in order to counteract this change in temperature. This will get rid of the stimulus and shut the feedback loop off.
What is the ideal situation for production of a species? Is this the reality? What can be done if this is not the reality to survive?
What is the ultimate goal of an energy budget?
The ideal situation for the reproduction of a species is to have unlimited resources to support maximal growth and a long life and a continuous production of offspring, to grow that population to the maximum. But of course many other factors come into play that inhibit this, such as energy being used to find food, to reproduce and to survive, and energy is not limitless. Therefore, an energy budget must be used to balance this energy across the many different places it is needed, and hence survive.
If you survive but don’t reproduce, you are an evolutionary dead end, but if you reproduce a lot and then die, you can’t contribute to the population and help your offspring survive — both to the extreme is detrimental.
Ultimate goal of an energy budget is to have enough energy left over to allocate to reproduction.
What is a life history trait? Life history strategy? What led to the development of these strategies?
Life history trait: This is a characteristic that the organism has that affects the organisms fitness and relates to the timing and occurrence of various key life cycle stages. Specifically, their size and age at sexual maturity, age specific survival rates, growth rate and patterns of dispersal, and lifespan. These all determine its fitness and are individualized based on many factors.
Life history strategy: This is the set of strategies outlined above which define how an organism allocates its resources and experiences throughout its life — so how it utilizes the above traits to survive most efficiently. This was shaped by natural selection — based on what type of lifestyle kept that specific species alive the longest or producing the most offspring.
What in the past shapes what in the future?
What things may change these factors in the present?
Success in the past shapes the life history strategies of the future. This is because by trying out different patterns of growth, development and reproduction, natural selection was able to chose specific traits for each species, which allowed it to be the most “fit” in its environment. So whatever traits allowed previous generations to survive and reproduce were clearly effective and hence were passed onto the next generation and hence determine the life history strategies that are used to be fit.
The environment can change the life history traits due to changing resources available, and hence those organisms may need to shift their patterns in order to survive in the changing environment.
What are tradeoffs and why are they essential?
Tradeoffs are when the energy put into one trait is taken away to be put into another trait. These are essential because energy budgets are fixed due to competition in the environment, and hence each species much chose where they want to allocate their energy in order to be the most successful and “fit”. As well, selective pressures in the environment can shape how these tradeoffs occur, especially if an organism is being continuously hunted, it cannot spend energy on reproduction as the young will die. It must spend energy on survival until the predator population decreases and then it can go back to reproduction.
Overall, if you spend energy on one factor, you will lose the energy available to spend on another factor.
Spend more money on growth — you might be eaten because you are not protected.
Spend more money on defence — you wont grow as well and have as much energy saved to reproduce as much.
If 2 _______ ________ __________ compete for a share of _________ _______, then its is impossible to __________ __________ __________ simultaneously.
If 2 life history traits compete for a share of limited resources, then its is impossible to maximize both traits simultaneously. One has to give up some energy reservoir for another, and this is all based on natural selection and current selective pressures in the environment.
ANY GAINS BY ONE TRAIT WILL RESULT IN A LOSS BY THE OTHER.
THIS IS BECAUSE BOTH TRAITS CANNOT BE MAXIMIZED SIMULTANEOUSLY!!!
What does a graph of fitness V.S. Number of seeds produced look like? Why? What about fitness V.S. Size of seeds produced? Why? What about seed size v.s. Number of seeds produced? Why?
Graph of fitness V.S. Number of seeds is a linear upwards line, where as the number of seeds increases, the fitness of the plant will greatly increase, as it is increasing the probability of one of those seeds planting in the ground and growing a new plant.
Graph of fitness v.s. Seed size will also be a linear upwards line, because as seed size increases, they will have more energy in each seed and hence will be able to more easily burrow into harder ground. So each seed has a higher chance of growing into a new plant.
Lastly, number of seeds vs seed size: As the seed size increases, number of seeds produced has to decrease, because the plant is putting energy into producing more seeds, and hence there is not enough energy to increase their size. The same happens in the opposite direction. Therefore, this graph is a linear downwards line, so that as one trait is maximized, the other is minimized, and only if both traits are at a medium amount will they both be able to be optimized.
Plants will exists on a continuum along this line, and where they place on this continuum all depends on the environment they live in.
What is indeterminate growth? What about determinate growth?
Indeterminate growth: Growth of an organism continues throughout its lifespan, so never reaches an “adult size/ maturatity”. Therefore, it spends a little energy throughout its entire lifespan on growth.
Ex: Ectotherm — reptiles, fish, plants, etc.
Determinate growth: Growth stops once an adult size is reached, and so it spends a lot of energy on growth at the beginning, but then spends none later on in its life to focus on reproduction and other strategies.
Ex: Endotherms such as birds and mammals and humans (only spend energy on maintenance growth).
What is asexual reduction? Sexual reproduction? Advantages and disadvantages of each?
Asexual reproduction: When they produce clones (exact copies) of themselves by only reproducing within that organism. So this involves budding, mitosis, binary fission, vegetative propagation (grows roots underground which sprout into a new plant) and fragmentation (parent plant breaks into fragments and each fragment turns into a new organism).
Advantages: doesn’t rely on finding a mate and so can replicate at any time, population can increase rapidly in favourable conditions, more time and energy efficient because don’t have to spend energy on finding a mate, and it is much faster.
Disadvantages: Limited genetic diversity, so if something changes in the environment it will wipe out the entire species. Harmful mutations in the parent are ALWAYS passed onto he offspring and this can accumulate over generations rather then being phased out (due to natural selection in sexual reproduction when different traits can be chosen from). Inability to adapt due to lack of variance in traits, short lifespans, and disease is easier to transfer between parent and offspring. Evolution cannot have as much of an effect.
Sexual reproduction: When they produce recombinant of the two parents, and hence requires two mates whose traits are mixed and chosen for by natural selection, hence evolving to produce the most efficient offspring over time. In this case, replicated genomes are halved into gametes and then these are shared between the two parents to produce a zygote.
Advantages: There is genetic variation which allows for different genes to be shown and hence the best traits to be selected for. Disease will not affect the entire species as it is not necessarily one of the genes passed down, and so natural selection will also phase out organisms with that gene so it is not passed down. It can also combine mutations into beneficial ones that can increase the organism’s fitness. Also allows for selective breeding, so based on traits that will help an organisms fitness, various mates will be chosen. Allows for evolution to chose certain traits and create more fit individuals!
What is the main tradeoff that is very important to all organisms? Why can’t both be maximized?
The main tradeoff that is very important to all organisms is the energy put into growth of that organism VS the energy put into reproduction. As one increases, the other must decrease because there is a total amount of energy present and you can’t have a lot of both. Therefore depending on the environment, different species will maximize different things. Therefore, growth rate and reproduction are inversely proportional.
How does parental investment in offspring and amount of offspring produced relate? Is there a tradeoff here?
Here, as parental investment in each offspring increases, the number of offspring produced total will increase, because you can not have so much energy that both can be maximized. If you put a lot of energy into taking care of offspring once they are born, then you can only have a few offspring that are larger, as that energy cannot be both concentrated and dispersed at the same time.
Then if you put a lot of energy into producing a bunch of offspring, you won’t have enough energy left to take care of your offspring once they are born. SO in this case you put a lot of energy into making many, to increase the chances of more offspring surviving.
What is another tradeoff that relates just to the parent alone?
Well the more energy you put into offspring, the less energy you put into yourself. Therefore, more of the food you collect goes into your babies development, and less into your own. plus when you are out collecting food and are powered by less food, then you will be weaker and less likely to survive yourself.
So it is a balance between living long enough to help your offspring grow up, and also giving your offspring enough energy to grow up. So the longer you live, the less energy that is going into your offspring, but the shorter you live, the more energy initially going into offspring, it’s just they may not survive as long.
Of course we want to live as long as possible, but this would result in us being an evolutionary dead end which is not desirable.
Semelparity is…
Iteroparity is…
“Parity” means…
Semelparity are individuals of the same species that can breed only once in their lifetime, and hence they spend a LOT of energy into that breeding. A lot of the time this leads to death of that organism once they reproduce. For example, salmon that do one long migration, give birth, and then die.
Iteroparity is when individuals of the same species can breed many times in its lifespan (has nothing to do with how many times they ACTUALLY BREED). So they may not spend as much energy in each birth but they can have more births overall.
So this does include humans, even if that human has only had one offspring, because they could have had more if they wanted. For example also, salmon that make a short trip to have offspring and then come back — they don’t expend all there energy into getting somewhere far away to breed.
Does evolution favour larger organisms with respect to offspring production?
Yes it does, because larger organisms can take in more energy total, and they don’t need as much energy per gram body weight and therefore they have more energy to allocate to each egg or offspring.
therefore, organisms that wait to a later age when they are larger to produce offspring will produce the most eggs, and this will increase those egg’s chances of survival.
Tradeoff between mating and lifespan…
So as mating goes up, a lot more energy has to be spent on finding the mate, doing the mating, and then actually giving birth. Therefore, those who mated lived A LOT shorter then those who did not mate, however they would have been more fit as they were passing on themselves to the next generation.
How does predation affect life history traits?
Well if there is more predation, then the organism can’t spend as much energy on reproduction or other traits, they have to focus on defence to survive.
For example, with guppies, the lower the elevation of the pond, the more predation there is and hence guppy size at birth must be smaller because those mother guppies are spending more energy on defence and less on reproduction. This then means that the fitness of those guppies decreases because the offspring are smaller and cannot survive as well in these high predation environments. More energy spent on current generation = less spent on future generation.
But for guppies at higher elevation, there is less predation and so they don’t spend as much energy on defense and hence can spend more energy on offspring size, giving those offspring a better chance to survive on their own. Or they can make more eggs total, increasing the probability that some eggs will survive.
What is a survivorship curve?
For Daf-2 mutation in C. Elegans, they lived 2x as long as the normal C. Elegans. So why wouldn’t this occur for all C. Elegans?
This is a curve that plots the percent of organisms alive x days after hatching. Therefore it shows how that species survives throughout time and what ages it declines in population most rapidly.
Now why don’t all C. Elegans live that long? Well this is because the longer you live, the more energy you are putting into your own survival and the less into offspring. Because you don’t produce many offspring, only a few will survive in comparison to the shorter life C. Elegans, and so they will have more offspring that will outcompete the offspring of the longer life ones. This results in a quick outcompete on of that mutation until there is none left.
What is the continuum that life history strategies reside on, and what are the two extremes?
This continuum contains the various traits that different organisms use to survive based on their environment and what traits they favour. Specifically, the two ends are r-selected and k-selected species.
What are the features of r-selected species?
R-selection:
-Produce ALOT of offspring at once, increasing the number of offspring that will survive (ratio for those surviving to those dying is constant, but the number of those surviving will be larger since both sides increase).
-Small offspring and adult size because so much energy is put into reproducing many, which comes with a tradeoff of how much energy goes into each species.
-Early sexual maturation and short lifespan, so they don’t grow to be very larger and hence can’t put as much energy into their offspring.
-Semelparous — one big birth at one time in life
-High fecundity (capacity of an organisms or population to reproduce), because they produce so many this value is HIGH.
-Low parental investment in each offspring, just a lot in the birth as a whole but after that it is all based on natural selection which ones survive.
-Low juvenile survivorship, but those who do survive have been selected because they have specific traits that allow them to survive for a long time.
What are features of K-selected species?
K-selection:
-These are super competitors, because so much energy is put into each organism that they have the tools to help them survive for a long time.
-large offspring and adult size, because the tradeoff favours size of each offspring rather then number of offspring
-Late sexual maturity, allowing them to grow to be very larger and hence put more energy into offspring (as they are taking in more energy) and hence produce larger offspring.
-Iteroparous: Can reproduce many times in lifespan, but each time only produces a few offspring (energy distributed over time not all at once, allowing them to focus on keeping the offspring they do make alive).
-Low fecundity (don’t produce many offspring)
-high parental investment (means that they ones that are born survive longer, and this increases the probability of their survival, not the total number of offspring that will survive as in r-selection).
-high juvenile survivorship due to lots of parental investment
-Long lifespan
-evolved to compete
What is a life history table and what is it used for?
A life history table summarizes information on age structure within a cohort, size, life-history (reproductive) traits, and the survivorship of a population.
It is used to manage crops and livestock, to see what is killing off animals and at what point in their lifespan this is happening, and also what can be mitigated to prevent this. It is used to predict how population will change over time.
What does each row of a life history table mean? (Don’t explain how to calculate them yet)
X
Nx
Sx
Ix
Mx
Ix x Mx
Ro
Each part of the table affects other parts of the table.
X is just the years that the specific cohort has been followed (starts at year zero for initial conditions). This is the factor that each other dependent factor changes based on. It is the manipulated variable.
Nx = #females at each age (x). This will not increase because we aren’t looking at any new things produced. We are just following a specific cohort through time, and seeing how they change. It doesn’t matter if they produce any one new, because this would just make up a new cohort. We are only looking at the original, and therefore this number MUST ALWAYS DECREASE.
Sx: Survival rate from one age to the next. So what ratio of those alive in the current generation will still be present in the next generation? So this ratio changes based on how many are alive from the current generation, and how many are alive in the next.
Ix: This is the survivorship, or how much of the original cohort are still alive. So not based on the current generation and the next one, but instead based on the original (time zero) population, and then the current generation, and what fraction of the original this is.
Mx: This is the fecundity (how well/fast they reproduce). Therefore, this is the average number of FEMALE offspring that each female produces in the cohort. We are only looking at the females because they are easier to track and they are the ones that reproduce, so the men that are produced are really dependent on the females for mating. So only the females being produced can truly indicate how many females are produced next generation. So whatever this value is, this is how many (female) offspring each (female) individual produces.
Ix x Mx: This is the ratio of individuals left compared to how many there was at the first generation, multiplied by the number of offspring being produced per individual. This is because lx is the probability of living to that age, and then multiplying this probability by the average number of individuals produced at that age, gives how many individuals are likely to be produced total. This value is equal to Ro, which the net reproductive rate, or the average number of female offspring produced per female in the cohort over the cohort’s lifespan. So it takes into account normal mortality within the cohort as well as what age is the most common reproductive age.
What does Ro indicate, and what does an Ro value =1, >1, or <1 indicate? How is Ro calculated?
Ro indicates the growth rate of the population based on the net reproductive rate of that cohort being studied. So if the Ro value is equal to 1, that means that on average each individual is replicating themselves and therefore the population would stay stable, not increasing or decreasing. If Ro <1, then each individual is not quite replicating themselves, and so the population will be shrinking. If Ro>1, then each individual is producing themselves and more, and so the population grows.
Ro is calculated by finding Ix times mx in each row, and adding all these values up to get the average. If you do this all the way until Nx=0, that means that entire generation is gone and you can see how the generation produces over their entire lifespan and essentially how they replace themselves. In other words, this is the measure of population growth rate per generation., or the number of female offspring that each female will replace over her lifetime on average.
We add them all up because we want to know the total number being replaced over the whole generation not just Ix times Mx for one row. We want to know how many are replaced over the lifetime based on how many are alive in each age group.
