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Ecology 7.docx

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Biology 2483A
Mark Moscicki

Ecology-Lecture 7 Oct 3 2013 Life History  Sequence of live events in an organism. (growth/development/reproduction/death) We are interested in all of these factors. For a human, you go through a period of growth and then you reproduce. On average, you live to 80. Our perception of life history is biased based on our experiences. However, many organisms experience very different life histories.  Life history characteristics include: age and size at sexual maturity, amount and timing of reproduction, survival and mortality rates Clown Fish Case Study-FINDING NEMO  Clown Fish hang in sea anemones for protection. Anemones sting the predators of clownfish, but not the clownfish themselves. The fish also benefit the anemone by eating its parasites or driving its predators away.  Usually 2-6 will hang out in one sea anemone for their entire adult lives. However, it is unlikely that they are related.  Largest clownfish is female. Next largest is the breeding male. All other fish are immature non breeders. They are simply biting their time waiting for the others to die off so that they can take their place. (based on body size) In finding Nemo, his mom died. If this actually happened, his dad would have turned into a female. If female died, breeding male would take her place and the next fish in line will become the breeding male.  Hatchlings move out of the anemone, and Figure 7.23 Clownfish Size Hierarchies juveniles must find a new anemone to inhabit. The reef is dangerous for them. They grow in open water and then come back to the reef to find open spots in anemones. When a juvenile enters an anemone, they are only able to stay if there is room. Why do the Clownfish Maintain the Heirarchy?  Clown fish are dependent on survival of being around anemone. (colorful and slow) They are easy prey outside of the anemone. If you are small and you try to change things, you get pushed out of the anemone and get eaten. You see through natural selection that aggressive clownfish do not end up reproducing.  Therefore, there is strong selection pressure to avoid conflict. Sea anemones are a scarce resource for clownfish.  Clown fish have growth regulation. They are able to avoid conflict by making sure they do not grow too big at any one time. (allows them to ensure they live to an age in which they can reproduce) Life History Diversity  Within a species there is a lot of diversity. There are genetic differences, differences in their environment and differences in their life history. Life history is a record of major events related to its growth, development, reproduction, and survival.  Individuals within a species show variation in life history traits due to genetic variation or environmental conditions.  The life history strategy of a species is the overall pattern in average timing and nature of life history events. Life decisions are made but these are genetically decided. (How many offspring and how big are they going to be? Are you going to care for offspring? How long to live? )  Natural selection favours individuals whose life history traits result in their having a better chance of surviving and reproducing. An organism predisposed to do certain things may or may not be selected for. Optimal Life History  Most organisms you would think would converge on a certain optimal life history to maximize their fitness (genetic contribution to future generations). However, it is not perfect. This comes down to ecological tradeoffs. Phenotypic Plasticity  A certain life strategy may be favoured under some conditions and not favoured under other conditions. You can only allocate resources in one direction at any one time.  This is why there is environmental plasticity. There is a certain amount of plasticity in any organism where they optimize how they grow/reproduce in respond to the environment  Environmental conditions can produce different phenotypes from the same genotype. One example is growth and development. You tend to grow faster at higher temperatures.  Individuals of a pine tree species are separated into 2 populations based on the environments in which they grow. (Ones that grow in cool moist and ones that grow in desert.) For any given height, you have a thinner diameter trunk for cool areas and a larger diameter trunk for desert trees. This is due to species physiology. Dry environment trees need to conduct water so the wide trunks allow them to have a lot of root/vessel elements so they can draw up water. Changes in life history traits can cause change in adult morphology. Morphs  Phenotypic plasticity may result in a continuous range of sizes; or discrete types called morphs (ALL OR NOTHING) There is nothing in between. Depending on the environment, you assume one of two phenotypes (another form of environmental plasticity)  You can call it a polyphenism in this case because you have one genotype that can produce several distinct morphs.  An example of this is toad tadpoles. We have omnivore morphs and carnivore morphs. (both from same genotype)What they develop into depends on the food they consume in early development. Depending on the pond they are in, they can become omnivore morphs and feed on detritus and junk at the bottom of the ponds, or they can become carnivores (large jaws) that feed on fairy shrimp in the water column. Carnivore tadpoles tend to grow very fast and they morph early. This is because they live in semi permanent ponds (ephemeral ponds). It is to your advantage to get out of the pond as quickly as you can so you do not dry up and die before you gain enough energy to turn to frogs and get out. Omnivores grow slowly because they dwell in long lasting ponds. When they eventually turn into toads, they are much better conditioned that toads from carnivore tadpoles (better survival)  Different body morphs result from different growth rates of body parts in both the Ponderosa pines and spadefoot toads. This is known as allometric growth. Allometric growth is when growth of certain body parts is favoured over others. Allometry is when different body parts grow at different rates, resulting in differences in shape and proportion. Modes of Reproduction  Asexual Reproduction: Simple cell division (binary fission) All prokaryotes and many protists do this.  Some multicellular organisms reproduce sexually and asexuallly (coral) Life Cycle of a Coral  Coral starts with larvae that forms pollup. Then it forms asexual units on top. This is why coral takes so long to develop (laying down carbonate for asexual growth from a single pollup) There comes a time when they undergo sexual reproduction. They give off a sperm and an egg producing larvae sexually which then forms pollups. (life cycle) Benefits  High genetic variation so you can respond to environmental changes. Asexual reproduction gives you many identical units. If the environment changes, you are not well adapted, everything dies Disadvantage  You are only passing on half of your genetic information to your offspring. You get lower population growth rates. Half of the offspring produced by the sexual females are male and must pair with a female to produce offspring. Therefore, asexual individuals increase in number more rapidly, and after 7-8 generations almost 100% will be asexual. The Cost of Sex Sexual Reproduction  Gametes of different sizes is common. Eggs are large due to their nutritional value. Most multicellular organisms have gametes of different size. This is known as anisogamy.  We can also have identical gametes (isogamy)Green algae does this! Complex Life Cycles  We see a relatively simple life cycle for most organisms (no major body changes or abrupt transitions) However, for many organisms like amphibians and insects/plants/algae/protists/fishes and marine invertebrates we get complex life cycles.  The small early stages of many animal life cycles look and behave completely differently from adult stages. They frequently eat different foods and prefer different habitats.  Complex Life Cycles: There are at least 2 different stages with 2 different body forms that often live in 2 very different habitats. They often go through metamorphism which is an abrupt transition in between the larval and juvenile stages. Many organisms in the ocean like plankton float around in larvae change and then after metamorphosis they attach somewhere and become a much larger/different organism.  Complex life cycles and metamorphosis result when offspring and parents are subjected to very different selection pressures.  In terms of our cells, we have direct development. Fertilizing develops into a juvenile without passing through a larval stage. Juvenile is mini version of an adult. (laying eggs which directly hatch into a juvenile) Classifying Life History Strategies  How many reproductive events will happen within a lifetime?  Semelparous: Species reproduce only once. These species include annual plants (complete life cycle within one year or less-After they germinate from a seed, they reproduce once and die) and Agave. Agave grows a vegetative leaf for 25 years, then they flower and die. However, at the same time Agave is reproducing sexually it also reproduces asexual clones on the ground. (same genetic info as plant-flowers produce clumps of seeds that drop off and root around the parent plant) The tree lives on through these clones. In this sense, they are not semelparous at all!  Iteroparous: Species reproduce multiple times. These species include pine trees and spruces which must put seeds out every year. Large mammals also typically have multiple reproduction events throughout their life. R Selection and K Selection  These strategies describe the two ends of a reproductive system continuum  R: Intrinsic rate of increase of a population  R Selected: For high population growth rates; an advantage in newly disturbed habitats and uncrowded conditions. You start out with a population, there is a lot of open space and very few individuals. There is a premium on reproducing quickly so the population can grow. R selected species can be considered "live fast die young" They have short life spans, rapid development, early maturation, low parental investment, and high reproductive rates. Most insects and small invertebrates (mice & weedy plants) are R selected  K: Carrying capacity of a population  K Selected: For slower growth rates in populations that are at or near K; this is an advantage in crowded conditions; efficient reproduction is favoured. When population is in growth (r phase) You will actually reach a point when all of the space is taken up and the population stabilizes ( k- carrying capacity) At K the population has reached stable equilibrium value and no more expansion can occur. K species must be able to
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