Types of adaptations
As previously seen with plants adapted to wet or dry conditions, different species employ a variety of adaptations to match their environment. The sum of all adaptations comprises behavioural, physiological and morphological adaptations.
The kangaroo rat lives in a dry environment
This lil’ fella is an adorbsssss little mammal that lives in North America in very dry/desert-type areas. It is a master at preserving its water, and can live without ever actually drinking water at all. Some of its adaptations are behavioural such as being inactive during the day and being active at night when it’s colder, as well as burrowing into sand, and bathing in sand to keep its hairs free of too much oil which would decrease their ability to insulate the body.
Other adaptations regard the kidney itself and are morphological, specifically very long loops of Henle. They allow longer filtration processes to take place, which allows as much water as possible, to the extreme, to be reabsorbed. Their urine is very small in volume and extremely concentrated in urea (physiological adaptation), up to 10 times more concentrated than a human’s.
They also obtain water from their metabolic oxidation reactions in cells, up to 90% of all their water. The remainder comes from food such as seeds. Oh, and by the way, if they weren’t adorable enough already – they’re called kangaroo rats because they jump like a kangaroo, can you imagine??
Herbivores adapted to a high cellulose diet such as ruminants have specialised teeth. They do not have incisors which are used to tear flesh in carnivores. Instead, they have a dental pad that helps chew plants, constituting a morphological adaptation. Looks so weird, took me a while to understand what was going on.
To help with the constant grinding, their teeth also grow continuously. This s a physiological adaptation.
Investigating organisms in the field is a way of exploring their adaptations without removing them from their habitat.
Sampling of organisms must be like those annoying, attention-seeking Snapchat friends. It must be random. Random sampling can be carried out using quadrats. If you’re wondering what they are, look no further – they’re squares.
How would you make sure that your sampling is random? In a field, you could lay two long tapes perpendicularly to define the limits of the area where the samples will be taken from.
As you can see above, a tape is laid on one side of the sampling area. As you can’t see above, another tape is laid from one end of the first tape, across on the adjacent side of the sampling area (like a giant L). Then two random numbers are generated using a random numbers table. These numbers are used to determine the coordinates of the first quadrat placed on the field, by matching them on the two tapes. And voila! You have yourself a system for random sampling using quadrats.
Transects are tapes (like above) placed across an area which has some form of gradient caused by abiotic factors which directly determines the distribution and abundance of the organisms present. For example, a beach is not suited for random sampling because there are clear zones ranging from the low population zone near the sea, to the more densely inhabited areas further up the shore. In this case the best way of obtaining useful data is by systematic sampling.
After placing the tape across the shore, place quadrats at set intervals such as every 5 metres, then take your data down.
Monitoring indicator species is central to classifying vegetation as well as assessing the health of a community. Indicator species can communicate through their absence, presence or abundance whether certain environmental factors are playing certain roles in the habitat at a given time. For example, pollutants can impact indicator species, so how the species is doing can be used to determine what the level of pollutant is currently in their environment.
Eutrophication is a good example of a factor that could alter vegetation type, and give rise to indicator species. This information could be used to assess unknown habitats. Vegetation types, such as different types of woodland, can also be established through indicator species e.g. Carex rostrata (bottle sedge) woodland.
Mobile species such as shrimps can’t be counted by the quadrat method. Instead, they are investigated using the mark-release-recapture method. This is something I personally did on my field trip for A level:
1. Capture shrimps using nets and count them.
2. Mark them by nipping half their tail diagonally (not proud :D)
3. Repeat, ensuring to account for the marked shrimps.
The more marked individuals you get, the smaller the total population is likely to be.
In order to calculate this, we can call the number of initially captured individuals M, and the number of those captured the second time C. The recaptured ones (with the mark) in the second sample C can be termed R.
This gives the equation N = (MC) / R where N is the total number of individuals in the population.
For example, if we caught 45 shrimps, marked and released them; then caught another 45 of which 31 were marked, then the total population would be:
N = (MC) / R
N = (45 x 45) / 31
N = 65.32 [shrimps are whole numbers so round down] N = 65 shrimps
The total population obtained this way is an estimate that depends on an equal probability for all individuals to be recaptured, and no migration into and out of the population to occur. Juvenile individuals might not be captured, ill individuals might not be captured, or the population might be connected to others, skewing the data from the mark-release-recapture method.
Methods of marking different species include banding, tagging, surgical implantation, painting, hair clipping, etc. Any marking method must minimise impact on the species, both during the marking process but also during subsequent observation through the mark.
In the case of elusive species that can’t be handled directly, camera traps are used to monitor them. Another method is scat sampling which involves taking a sample of faeces left behind on the ground. This is used for cheetahs. Something to bear in mind is to not take all the scat available, as it is used by the animals as a territory mark.
Trained dogs can be used to assists with scat finding. The sample can be analysed genetically to establish how many different individuals are present in the area.
Depending on the size and type of organism, data can be collected in the form of numbers by counting the present organisms in each quadrat (frequency), or working out the percentage of area within a quadrat that a species occupies (percentage cover), then scale it up to the whole area investigated by multiplying.
For percentage area, you’d count the smaller squares within the quadrat that your target species covers, and convert that number to a percentage (there are 100 smaller squares in the quadrat). So for example, our green plant would cover approximately 25 squares, giving us a 25% coverage. Both these methods are quantitative, giving us 11 plants per quadrat and 25% quadrat coverage, but there is another less quantitative, more descriptive method called ACFOR.
ACFOR is a somewhat subjective system for describing the abundance of species within a quadrat. It follows:
A = abundant
C = common
F = frequent
O = occasional
R = rare
Based on this, we might describe the above scenario for the green plants as perhaps, frequent. Are they common instead? Maybe just occasional? Hard to tell, and dependent on what the overall area looks like, and what other species there are.
This is why it is important to select the appropriate ecological technique for the ecosystem and organism to be studied. For example, if our area contains many different species with scattered distributions, we are likely to get many different numbers for each, which might take a very long time, and might not be that necessary for our analysis. Perhaps we are only intending to compare whether two species are equally abundant or not.
In that case, we wouldn’t be spending time counting small squares to get a percentage cover, but rather using the ACFOR scale. Another scenario is looking at very small species that we cannot count individuals for! Think grass. We would use a percentage cover or ACFOR in this case.
In another case, we might have a scarce area with very few individuals for each whole quadrat, nevermind little square within. In this case we might prefer to simply count them rather than try ACFOR which wouldn’t work because it’s too generic and we might end up with all “R”s, or percentage cover which would also mostly be totally empty and give 0% for no individuals present, or 10% if one quite large individual is present that covers many squares. In this case, counting would give the most useful data as we would get a few whole numbers, e.g. 1 for the first quadrat, 0 for the next, 2, then 5, then 1.
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