Theme 3 Flashcards
Define the terms community, assemblage, and guild from an ecological perspective.
A community is all the biota within a particular geographic environment, interacting with each other and the environment itself.
An assemblage is a group of phylogeneticaly related biota within a particular geographic environment (e.g. all the various seaweeds in the north sea).
A guild is a group of organisms that use the same resources or method of obtaining a resource (e.g. filter feeders).
Explain the fundamental and realised niches of organisms, and the total niche of ecosystems.
The fundamental niche of an organism is the full range of environmental conditions and resources that it can occupy and use. The realised niche of a species is the set of biotic and abiotic resources that they actually utilise after competing with other species.
The total niche is the sum of all the biotic and abiotic resources within a particular environment which are there to be exploited, and it is partitioned among species, whose relative abundance reflects the proportion of the niche they occupy.
Discuss the 4 main theories as to why bats are the sources of so many zoonoses. Refer to findings of some recent studies to evaluate these theories.
1) Bats have a “special” relationship with viruses due to their evolution of powered flight, which results in inflammation and immunity. Particularly high metabolic stress on bat cells, which would normally lead to high degrees of inflammation, do not - their inflammatory response has adapted to cope with the metabolic stress of flight, and as such, they may resist over-inflammation when infected with diseases.
2) Flight may create a nightly artificial fever due to its metabolic cost, and this may decrease viral loads. Since bats usually torpor during the day, the body temperature is subject to massive changes between day and night, and this may be unsuitable for the viruses to be dangerous to them (however, this theory is not widely accepted).
3) Bats tend to live in huge colonial aggregations (which can contain several species), they fly (unlike other mammals), which connects populations which otherwise may be isolated, they defecate over populations of other mammals, and they regularly capitalise on human resources - these ecological traits may provide optimal conditions for viruses to spread via bats, especially to humans.
4) Bats are the second most species rich mammalian order with >1400 species. This may simply be a numbers game, where the number of bat viruses can be explained simply by their abundance and variation, without invoking any immune or behavioural traits.
Explain some potential future approaches for managing viruses emerging from bats.
There are 3 stages to disease emergence, which must all be addressed - the virus must be maintained within its natural host, have the opportunity to jump between species, and be able to infect a new host.
1) Culling or vaccinations present a solution to the first stage - vampire bats are commonly culled using poisonous gel which is rubbed on them. They then ingest this when grooming each other.
2) Preventing infectious contacts by educating people can solve the second stage.
3) We can’t prevent a virus from mutating to infect us or domesticated animals, but once it has done, we can develop vaccines and post-exposure treatments to deal with these zoonoses.
Many management regimes regarding zoonoses are reactive, meaning that we only tend to deal with them after they have already occurred. By shifting our focus to be preventative, we may be able to reduce the frequency of zoonoses from wild animals.
An oral vaccine has been suggested in order to vaccinate vampire bats from diseases such as rabies, which they spill over to domestic animal populations. Similar to the poison gel, this would be administered on the fur of several individuals and would then spread through the colonies when grooming occurred - a mock of this has been conducted already using a fluorescent dye called Rhodamine B.
Describe and explain the 3 types of survivorship curve, and give examples of each.
Species which exhibit type I survivorship begin life with a very low chance of death, which increases gradually as the individual ages. Death usually comes from senescence and wear-and-tear. Examples of this include humans and elephants.
In type II survivorship curves, individuals have a roughly equal probability of death throughout life. This includes most small mammals and birds.
Type III survivorship curves have huge mortality rates following birth, which gradually reduce as individuals mature into adults. Examples include arthropods and cephalopods.
Explain how the principle of allocation leads to adaptations of different life-history trade-offs. With reference to this, explain the terms r- and K-selected species.
The principle of allocation states that there is a finite amount of resources (time and energy), and different activities compete for the same resources. As such, optimal reproduction strategies of fast sexual maturing, many offspring, and high investment into offspring cannot be found in nature. This results in trade-offs of organisms in their reproductive strategies, which are known as life history trade-offs. There are two common combinations of life history traits which are observed in nature, and most species can be defined somewhere along a continuum between these two extremes:
r-selected species are small, short-lived, early maturing organisms which produce many small offspring (e.g. annual plants), whereas K-selected species are large, long-lived, late maturing organisms which produce few, large offspring (e.g. African elephants).
Outline some of the techniques which can be used by researchers to understand population dynamics.
1) Quadrants and line transects involve counting small sections of populations and extrapolating this to estimate the whole population count. These counts are repeated several times and in different locations in the interest of reliable, representative results.
2) Mark-recapture involves catching and marking individuals, then releasing them for a while and capturing more individuals at random. The ratio between marked and unmarked individuals allows us to estimate the total number in the populations, but this relies on assumptions that the population must be constant, that each individual in the population is equally easy to capture, that the mark does not harm the organism, and is not lost. Some organisms are naturally marked - this means that no external markings are required for this technique (e.g. humpback whales).
3) Abundance indices such as hunting statistics, droppings, tracks, and nests, tell us relative densities of populations but the relationship to the total population count is often difficult to estimate this way. Genotyping droppings can allow us to determine the exact individual in the population who left them. An accumulation curve can then be used, where the sampled faeces (x-axis) is plotted against the number of discovered individuals (y-axis). Using this, we can predict at that point the curve will level off, giving an estimation of the population size.
Using the example of culling red deer, explain how horizontal and vertical life tables can be compared to inform us of population dynamics and help make robust management decisions.
Life tables are essentially age pyramids translated into tables - they are age-specific summaries of birth and death rates.
Horizontal life tables are created by following individuals throughout time and recording their birth rates and deaths, whereas vertical life tables are created through longitudinal counts of the population (at one point in time), then the tables are constructed based on the individual’s ages.
Using life tables, we can calculate the basic growth rate of a population. If the two life tables, horizontal and vertical, do not yield the same results, then we can assume that the birth and mortality rates are not constant. For example, hunters suggest that culling red deer in compensatory to their mortality (i.e. the animals would die anyway of natural causes, so they are not affecting the overall mortality through their hunting regime). This theory can be tested by comparing the horizontal and vertical life tables of the red deer. When we do this analysis, we see that the horizontal life table estimates the expected distribution with mortality gradually increasing with age, whereas the vertical life table diverges from this, showing that there are very few older individuals - this suggests that hunting red deer is not compensatory to their mortality, but changed the age structure of the population.
Explain the phenomenon of logistic population growth.
Any environment will provide limited resources which the population needs to survive and reproduce - every ecosystem has a maximum carrying capacity which is determined by the amount of resources which must be shared across a population of organisms. This results in a logistic population growth (S-shaped). The maximum carrying capacity is known as K, and is the maximum number of organisms which can be sustained within the environment - the limiting factors are density-dependent processes.
Discuss the huge variety of migrations which many organisms take, and describe some of the key trade-offs of each.
Birds typically migrate north during Spring when the snow retreats, and then back south when the snow returns in Autumn, following the “green wave” of vegetation for feeding. Mammals also migrate - for example, Wildebeest in the Serengeti move to the wooded savanna during the dry season to exploit the humidity near the trees, and then move south to the short-grass savanna for fresh vegetation during the rainy season. These annual migrations require extreme trade-offs, as it is a challenge to travel such long distances with the excess fuel stores (fat) which is required for energy. Many routes therefore contain several refeulling stops.
Certain migrations occur just once per lifetime - for example, Eels lay their eggs at the coast of central American, and the plancktonic hatchlings are carried by the gulf stream for 1-2 years until they reach the Mediterranean, when they use magnetic and moonlight receptors to find fresh water in north-west Africa or western Europe. They then develop into yellow Eels then silver eels (around 30 years later), which are then ready to migrate back to central America via lower-down water currents, where they produce their eggs and die.
Some individuals don’t do the whole journey, but the migration occurs over several generations - for example, Monarch butterflies have several breeding ranges throughout the year. At the start of the year, the first generation adults move north from central America, lay their eggs and die in Spring, then the next generation eat, metamorphosise, and continue the migration north until they reach summer breeding grounds, and this repeats. Then, the third generation of adults moves southward in late Summer back towards central America, and the process starts again.
Some migrations are daily - for example, zooplankton eat phytoplankton during the night (0-100m depth), and then migrate to deeper waters during the day to escape predation (100-500m).
Explain the idea of dispersal, and outline some of the key modes in which organisms do this.
Dispersal is the spreading of individuals away from the main population, in any direction.
Passive dispersal involves the use of environmental factors to randomly carry seeds or planktonic larvae (e.g. ocean currents/winds). The vast majority of individuals will be carried somewhere which is not suitable, and will perish (generally associated with type III survivorship curves). Sometimes, passive dispersal relies on vector organisms (e.g. seeds dispersed through consumption and droppings).
Active dispersal involves organisms actively moving across land, air, or water through locomotion. This is normally intentionally done, but sometimes inadvertently to follow resources.
Breeding dispersal is active dispersal where breeding adults (typically females) move around males’ territories to breed.
Natal dispersal is a common type of active dispersal where juveniles disperse between a natal site and a site of first breeding.
Typically, dispersal does not go great distances, just to the nearest available and suitable site. Philopatry is the strategy of staying at home in stead of dispersing, and can be advantageous as organisms don’t take on additional risk of their journey into unknown territory, nor expend energy in doing so. Additionally, the familiarity of home, as well as locally adapted genes may make an organism more suited to its home environment, and this may also let them maintain kin selection. However, local competition will not be avoided, and inbreeding depression may occur.
Explain the concept of metapopulations, how dispersal can stabilise them, and how anthropogenic activity can affect their connectivity.
Dispersal can allow distinct populations of animals to emigrate and immigrate, such that they are constantly interacting with one another. Networks of populations which interact in this way are known as metapopulations. Unlike a continuous population, a metapopulation has spatially discrete local populations, in which migration between them is restricted.
‘Islands’ of suitable habitat are surrounded by a matrix of unsuitable habitat, within which mortality risk is high, limiting movement between patches. These ‘islands’ or ‘patches’ can be divided into source and sink populations. Source populations live in very high quality habitats which produce an excess of organisms which then go on to disperse into the sink populations, where organisms survive in a sub-optimal habitat. Sink populations receive more organisms that they donate, and source populations donate more than they receive, and so are only sustained as long as the source population remains successful and the corridors between the two (through the matrix) are unobstructed.
Anthropogenic activities can cause a large degree of disturbance in this matrix, and the advent of infrastructure and man-made habitat can prevent obstruct the corridors between sub-populations within metapopulations. The compromised connectivity therefore causes sink populations to die out, reducing the realised niche of the metapopulation, and potentially causing high competition and inbreeding depression within source populations.
Explain the effects of competition on relative species abundances and the main outcomes which take place in nature.
If many organisms are competing for a finite resource, they will exhibit a logistic population curve which tends towards a maximum carrying capacity for all organisms which interact with that limited resource (as well as their own maximum carrying capacities).
The competitive exclusion principle states that two species with the exact same needs as each other will not co-exist - one will always be a more successful competitor and will oust the other. As a result of this, species have evolved in a way which allows them to exploit resources differently (competitive exclusion of one species has forced it to evolve to occupy a slightly different niche in order to survive). This can include resource partitioning, where species specialise in specific elements of a resource, or at different times; or character displacement, where species evolve different morphologies in order to exploit different niches.
Explain the effects of predation on population dynamics, with reference to the orange universe experiment.
Over time, predators and prey are able to co-exist at equilibrium. This is due to the fact that predators will usually select the easiest individuals to prey on (old, young, weak, etc), meaning that the loss of these individuals has only a small effect on the reproductive value of the population as a whole. However, invasive species often result in extermination of prey as opposed to co-existence.
An example of this is seen in the orange universe experiment, where oranges were laid on a tray, some covered with petroleum jelly and other not, and each with a toothpick stuck into the top. A fan blows over the oranges, which are essentially islands for organisms to live on - mites climb the toothpicks and can be blown by the fan to reach other orange islands. Predatory mites and prey mites are released onto the tray, and their populations are tracked. Over time, the prey mites won out, because they were better dispersers than the predatory mites.
However, normally prey abundance will remain constant with proportion to the abundance of predators and vice versa, but with a slight delay, as reduced prey abundance when predators win out will result in more limited prey, which will then cause the predators to starve, the prey will then win out and their abundance will increase, and when there is plentiful food then the predators will become more abundant again and the cycle restarts. This is known as coupled oscillation, and is also exhibited by parasites and hosts, as well as herbivores and plants.
Explain the effects of commensalism and mutualism on population dynamics.
The species which benefits in commensalism has an abundance which is tied with the abundance of the species which is not affected - if there are not enough of the unaffected species for all beneficiaries, there will be competition for access to them, and those who are ousted will perish.
In mutualism, both species benefit from each others’ presence, and so rely on each others’ abundance for their own - this is a positive reciprocal relationship.
