17. Competition and Predation Flashcards
What is the importance of competition?2
- Underpins evolution 2. more offspring than parents, but competition balances out numbers
What is competitive exclusion? 3
- Two species cannot coexist if they occupy too similar a niche - one WILL go extinct. 2• Resource partitioning describes the differentiation of niches that allows species to coexist ie .parts of niche overlap but parts don’t. 3• We can investigate how sympatric species can coexist by looking at their niche overlap, as there are always subtle differences
What are some of the things that can be different to avoid two species having the same niche? 5
- habitat 2. size 3. feeding habits 4. geography 5. (seasonal) range
What is resource separation? 7
- Southwood (1978) defined a value d/w as the resource separation ratio. (distance and width between midpoints) •2. d/w 3: harmonious coexistence 5. However the picture is clearly more complicated than that because of multiple niche dimesions 6. niches may overlap in one measure but not another 7. calculations must include all niche dimensions
How can morphology allow two species to coexist? 6
1• To coexist species need to exploit non-overlapping niches. 2• This may push species to exploit resources at the edges of their niches. 3• Adaptation under natural selection may therefore favour morphology that can exploit these resources and generate character displacement. 4. genes for competition are selected against 5. better to be on niche edges away from competitors than in midpoint vs competitors 6. eg. different finches with same beak size can evolve different sizes and coexist.
What is the significance of predation? 4
1• One particularly extreme example of competition is predation. 2• Animals show many adaptations to avoid predation. 3• However it is still governed by similar population level rules. 4• The population numbers of predators and prey are tightly linked, therefore influencing ecosystem.
How might prey defend themselves from predators? 7
How do we find the prey growth rate with predators of a population? 3
This assumes that predators define carrying capacity
How do we find the growth rate of predators with prey?
How do the predator and prey populations influence each other? 5
- limit each other’s numbers
- if you being with low predator numbers, prey numbers increase, so predators increase
- this decreases prey
- leads to an oscillating equilibrium - no fixed numbers but coupled
- can plot as predator vs prey or predator and prey number and time
- pvp can be limited as does not account for other factors and oscillations can appear dampened
Why does the zebra have stripes (Egri et al, 2012)? 8
- Apparent size increase. The stripes may create a visual illusion that increases the apparent size of the zebra.
2• Visibility in poor light. In low light conditions (near dusk and dawn, or in moonlight), the stripes might be difficult to make out even from a close distance.
3• Moving stripes may dazzle predators. The moving stripes of fleeing zebras might make it difficult for predators to single out an individual zebra from the herd.
4• Camouflage. The stripes may allow zebras to blend in with their background (e.g. tall grass or savannah vegetation) by dissolution of their contour.
5• Social benefits. Since the stripe pattern is individual, as a fingerprint, zebras may recognize each other on the basis of their stripes. •
- Fitness indication. Irregularities in the stripe pattern due to disease, injuries or any kind of acute dysfunction might be a visual signal about the poor physical condition (fitness) of the individual for mate-seeking zebras.
7• Thermoregulation. The fat pattern in the skin may correlate with the pattern of black stripes, which might function as heat absorbers, and thus may play a role in the thermoregulation of the body..
8• Protection from tsetse flies. Zebras seem to be unfavoured hosts for tsetse flies.
How do striped protect zebras from tetse flies? 5
- Tested the pattern preference of flies
- looked at sebra skin, stripe orientation and thickness, and visual differences between humans and flies were considered
- Used fake zebra on farm in Hungary and tested horseflies
- The flies showed a strong preference for black, then brown horses
- stripes seemed to act as deterrent
How do extinction and conservation relate to ecology? 7
1• Extinction is a natural phenomenon but current rates are fairly high.
2• Ultimately extinction is explainable through ecological processes: competition, resources, climate.
3• Certain features of certain species make extinction more likely eg. rare species.
4• Identifying causes can help with conservation (prevention of extinction).
- Over time, extinction has not been uniform over taxa
- mammals and molluscs are especially susceptible to habitat destruction
- mammals aslo susceptible to invasive species and hunting
What are some factors that alter a species’ susceptibility to extinction? 4
What are some factors that alter an individual’s susceptibility to extinction? Part 2. 4
Strong specialisation of upper trophic levels makes them more vulnerable if something changes below
