Certain birds display a behavior called “broken-wing display” in order to divert the attention of a predator. Birds will display this behavior in order to protect their offspring. For example, consider a coyote is approaching a mother duck and her offspring. The mother duck is easily able to fly away from the coyote, but her ducklings cannot. In order to protect them, she will pretend as if she has a broken wing. She will act as if she is struggling to fly and lift off the ground, to get the attention of the coyote. Meanwhile, her baby ducklings will be walking away from the scene looking for a safe place to hide. The mother will continue this behavior, confusing the predator, to divert his attention away from her offspring until they are safely hidden. Once she sees her ducklings are safe, hidden where the coyote cannot get to them, she will quickly stop pretending her wing is broken and fly away. This is an example of how animals avoid predators, as well as an example of how a mother will risk her own life in order to save her offspring.
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The Beneski Museum of Natural History at Amherst College has an interesting display that shows the evolutionary history of the horse. The display has four skeletons that reveal how the horse has changed over the past 50 million years. The first case is of an ancient horse, about the size of a dog. The animal lived in a dense forest, where its diet consisted of leaves, berries, and parts of plants. As time passed, the environment began to change. The forests dried out and became grasslands, which also meant the horse’s diet had to change for its survival. Horses became grazers, eating mainly grass, and their teeth began to evolve to accommodate this diet. The crowns of their teeth became higher over time. Along with this change in dentition, was an increase in body size. One last significant change in the evolution of the horse is the development of the hooves. Bones fused, and the number of digits decreased, which optimized their ability to run. The four skeletons of this display show these changes in an ordered fashion, laying out just how the horse evolved over time.
In my mammalogy lab we went on a field trip to the Beneski Museum of Natural History at Amherst College. One wall of the museum showed skeletons of horses over the past 50 million years to display how horses evolved over time. 50 million years ago, horses were the size of dogs. They lived in forests and were omnivorous. As time passed, the environment started to change. The forests transformed into dry grasslands. With this change, the horses’ teeth began to evolve as they became grazers, who ate grass. The height of their tooth crowns got higher over time. Along with this change, they increased in body size. One of the most significant changes was the evolution of their toes. Horses eventually became unguligrade, walking on hooves to optimize running from predators. This happened by fusion of their bones and decreasing number of digits, until they only have one.
In my animal behavior class I am conducting an experiment about ant foraging behavior. I am testing how reliant ants are on social cues to obtain food. I hypothesize that ants are able to quickly and efficiently find a food source if other ants from their colony already accessed that source, and that they will follow this path even if it leads to a suboptimal food source. The first ants to access the source are called the “recruiters” and they will lay down a pheromone trail on their way back to the colony. I will observe the other ants to see how closely they follow this pheromone trail, scoring the number of times ants deviate from this path and exhibit “exploratory” behavior. Next, I will conduct a similar experiment, but I will wipe the surface clean to remove any pheromone trails laid out by recruiter ants. I will then allow the other ants to try to access the food source, again scoring the number of ants that show exploratory behavior rather than traveling directly to the food source. If the ants show a significantly higher amount of exploratory behavior after the surface is wiped clean than when it is left as is, this will indicate that the ants follow pheromone trails laid out by others to access food sources.
Once I have clearly shown that ants use social cues from others to access food sources, I will do a second half of my experiment to show how reliant they actually are on others. I will do this by first allowing the recruiters to access a safe food source, and go back to their colony, leaving their pheromone trail. I will then replace the food with a toxic food source. I will then score the number of ants that still follow the path even though the food at the end is suboptimal. If a significant number of ants still directly follow this path to the toxic source this will show ants are heavily reliant on others from their colony when it comes to foraging for food.
Fossils are direct evidence of the theory of evolution. They are a clear representation of what existed in the past. Fossils are found in layer of rock within the earth; the deepest layers contain the oldest fossils, and layers toward the surface contain more recent fossils. Furthermore, fossils found closest to earth’s surface resemble modern species, and as the layers get deeper, fossils show less and less resemblance to extant life. This is important evidence for evolution because it shows that life on earth has changed over time - the most fundamental definition of evolution.
Bipedalism is the ability to walk upright, on two feet, with eyes facing forward and not downward. This trait is a newly derived trait of hominins, which includes modern humans and our closest living relatives after the evolutionary split from chimpanzees. Before this, the ancestral trait was walking on all fours. Bipedalism evolved at least 3.2 million years ago, which is shown in the fossil record. Evidence of bipedalism in the fossil record includes a hole at the very base of the skull, where the spinal cord enters. Other evidence is the shape of the femur bone. Furthermore, the pelvis anchoring in leg muscles. Theories for the reason bipedalism evolved are to be able to see over tall grass, to get food from tall trees easily, and because being bipedal saves a lot of energy. These are all crucial to our survival. It is proven that gorillas expend about four times the amount of energy walk as humans do. A lot of energy is spent walking on all fours because they have to work harder against gravity. Walking upright may also lead to better thermoregulation.
Fossils are important evidence for the theory of evolution. Fossils are direct evidence of what species existed in the past. Fossils are found in layers of rock, the deepest layers of rock contain the oldest fossils, and the layers at the top contain the most recent fossils. Radiometric dating is used to determine the age of fossils, and confirm that the deeper layers of fossil are the oldest. Furthermore, the fossils close to the top resemble modern species of animals, and as you go deeper and deeper, fossils resemble modern species less and less. This is important evidence for evolution because it shows that life on earth has changed over time - the most fundamental definition of evolution.
However, as important as fossils are, it is important to note that the fossil record is biased. More recent fossils may be more likely to be found, because some may be too old for discovery. Species that lived in habitats that were more abundant are also more likely to be found. Also, the fossil record is biased because groups of animals with hard structures such as bones or shells are much more likely to fossilize. This means that there may be many forms of life that existed that did not fossilize, so we do not know about them.
It’s also important to know fossilization is rare. It only happens if decomposition is slow, and burial is fast. It also only happens if the structure being fossilized is resistant to decomposition, such as bones, pollen, and shells. Lastly, the more abundant the animal, the more likely you are to find a fossil of it.
Evolution is often constrained by functional requirements of structures. What this means is that if a structure must carry out a certain function, there is a limit on how much that structure can diverge from its original form. One example that illustrates this idea is the evolution of the marsupial forelimb. When marsupials are first born, they must complete a crawl to their mother’s teat. This functional requirement must be retained by the forelimb, which limits how much the forelimb can diversify, and specialize through evolution. This is proven when comparing the marsupial forelimb with the marsupial hind limb, and the eutherian forelimb. The marsupial forelimb is less diverse in each case, due to the functional constraint limiting its ability to evolve.
This paper’s methods included doing an extensive literature search on plant species composition, and richness, as well as composition of nutrients in plants to study how nutrient availability affects plant diversity and richness in temperate wetlands of North America. The data found was then put into spreadsheets and statistically analyzed to draw conclusions. A similar activity may be done in class by doing a literature search on abundant mosses of different areas and comparing them to the environmental conditions in each area.
Bedford BL, Walbridge MR, Aldous A. 1999. Patterns in nutrient availability and plant diversity of temperate North American wetlands. Ecology. 80:2151 – 2169. <http://onlinelibrary.wiley.com/doi/10.1890/0012-9658(1999)080%5b2151:PINAAP%5d2.0.CO%3b2/full>. Accessed 2017 Feb 28.
Evolution is often constrained by functional requirements that must be retained, which limits how much a structure can diverge from its original form. One example that illustrates this is the evolution of the marsupial forelimb. When marsupials are first born, they must complete a crawl to their mother’s teat. This functional requirement must be retained by the forelimb, which limits how much the forelimb can diverse, and specialize through evolution.
This idea was investigated by E. McKenna Kelly, and Karen E. Sears (2011), who tested two hypotheses to verify the argument that the evolution of the marsupial forelimb is constrained by the functional requirement of the newborn crawl to the teat. The first hypothesis formed by the two is that marsupial forelimbs are less specialized than eutherian forelimbs. The second hypothesis is that marsupials tend to specialize their hind limbs rather than their forelimbs, and that eutherians tend to specialize their forelimbs rather than their hind limbs. Testing this will prove whether or not the functional requirement of the newborn’s crawl to the teat has limited the diversification and specialization of the marsupial forelimb.
These hypotheses were tested using three functional groups, grouped by different modes of locomotion. The groups were analyzed using different statistical tests, and the results were in favor of both of the hypotheses. Marsupials showed more diversity in hind limbs than in their forelimbs, while eutherians showed more diversity in their forelimbs than in their hind limbs, which supports the second hypothesis. It was also found that eutherian forelimbs have diverged further from the average mammalian state than marsupial forelimbs. This means that eutherian forelimbs have become more specialized through evolution, because they do not have to retain the functional requirement of crawling to the teat at birth like marsupial forelimbs do.
Overall, Kelly and Sears experiment supports the argument that the evolution of the marsupial forelimb complex is constrained by the functional requirement of the newborn crawl to the mother’s teat. The experiment shows how functional requirements can have large effects on how much a structure can diversify through evolution. It is clear that some structures are free to specialize and evolve much more so than others, which is apparent when looking at how much more the eutherian limbs and marsupial hind limbs have diversified compared to the marsupial forelimb.