Field assessment of morphological and behavioural features of vertebrates in relation to their ecology.
Khalil Betz-Heinemann – DI308
Organisms exhibit behaviour as a means of enabling themselves to adapt specifically to their environment at any point in time that they exist (Allen 2006: Chp 4).. Each organism acts in a certain way. The reasoning for these actions or behaviours can be explained within a framework laid out in 1963 by Tinbergen. Within this framework an individuals’ behaviour can be seen as influenced by four factors; its’ specific morphological adaptations, its’ evolutionary history, its’ development in reaction to its gene-environment interaction and its’ specific cause for action at that time (proximate mechanisms) (Tinbergen 1963).
As natural selection sees to it that those species which are best adapted to their environment are the ones that survive, a behaviour which a species or individual exhibits must be efficient in maintaining survival (Allen 2006: Chp 4). As behaviour is directed by the four factors outlined by Tinbergen, it is also limited by them. Therefore individual specific behaviour is a balance between the limitations imposed by certain adaptations and the benefits they can deliver in terms of survival. Optimization theory has thus been applied in behavioural ecology to provide an analytical tool for studying behaviour within a cost/benefit scenario, thus providing a better understanding of how and why specific behaviours exist in the first place and how they develop (Smith 1978).
In this assessment the first Tinbergen factor mentioned; specific morphological adaptations will be looked at in vertebrates, in relation to the behaviour exhibited by the individuals observed (see Table 1). The habitat where observational data was collected is deciduous woodland in the South-East of the U.K. The location is made up mainly of clutches of the indigenous Oak and Hornbeam inter-dispersed between large patches of coppiced non-indigenous sweet chestnut. Some Holly and Yew trees are also present occasionally, along with a few re-claimed ponds. The data was collected between 2-5pm on the 2nd and 3rd of November in 2009, when the weather was sunny with a light chilly breeze and no cloud. The equipment used was limited to binoculars and writing materials and the data collected were the first actions exhibited by individual species as they were come across by the observer.
Health and safety guidelines were also taken into account as warm water-proof clothing was worn to ensure the observer’s ability to stay in the field if it rained and not contract any cold related symptoms. Additionally caution was taken by the observer when traversing the woodland as many rabbit warrens and gullies exist, so that no adverse effects from stepping in one would happen. No foreign materials were left to cause pollution and no unnecessary damage was done in traversing the woodland.
When looking at the data (Table 1) we can see that the first mentioned Tinbergen factor, of morphology as defining behaviour, is implicit among all the observations. If we analyse each species observed in turn we can see that the behaviour is always defined by its morphology, whether it be benefiting it or constraining the specific aim it is trying to achieve. We can also see that the other three Tinbergen reasons for specific behaviour play a major part in limiting or benefiting the species observed. If we look at the data we can see that the aims of each species can be split into two main categories; foraging and predator escape. (Temperature maintenance and sexual success are also two other main aims required for the survival of any species, however behaviours reflecting these were not observed in any great detail here). Each of these aims is then coordinated by the species behaviour using its morphology.
The Siskin observed was feeding on seed kernels stuck in a cone (Image 1). The reason for this choice of food is that its morphological adaptation of a long thin beak makes it efficient at obtaining this food source. However its evolutionary history also affects its behaviour as it cannot now feed on larger seeds that require a stronger beak to crack them. However the behaviour of choosing the specific tree it was observed on, is not only dependent on its morphology but by proximate causes such as availability of kernels.
Additionally it is possible its development has influenced its behaviour as it will have followed other birds and learnt that that specific tree has available food resources. We can see from this example alone that through using Tinbergen’s four factors we can construct a picture of why that Siskin was exhibiting that behaviour at that time. A similar relationship between Tinbergen’s reasons for specific foraging behaviour can be seen in the Rabbit observed. It had two highly specialist front incisors that are perfect for cutting the grass it was eating, however its choice of food source is now limited by its morphological adaptation too.
Another behaviour that was common between the two species was foraging timing. The Siskin only spent a certain amount of time poking into cones. If it could not retrieve a kernel it did not carry on trying to extract it but moved on. In the short term it lost out on that specific kernel, however on average it would gain more energy. This is because each kernel is only a small food source so to expend too much energy on extracting it is defeating the purpose of obtaining it. We can see that the actual characteristics of the food source not only influence the morphology of the Siskin (e.g. its beak), but also the extent of the behaviour surrounding the acquirement of it.
This type of behaviour is also exhibited by the Rabbit and can be explained by the Optimal Foraging Theory (Stephens 1986). The Rabbit kept on moving a small distance quite regularly when eating grass, even though it hadn’t eaten all the grass in the near vicinity. The top part of grass shoots contain the most nutrients and require the least amount of energy to digest. So for the rabbit to gain the optimum amount of energy it has struck a balance between expending a small amount of energy moving and getting the most nutritious grass.
Statistical analysis and Optimal Foraging theory suggest that animals such as Rabbits behave in such a way as to benefit from this balanced of behaviour as efficiently as possible (Krebs 1978).
Upon being spotted by the observer, the Green Woodpecker was observed crawling around the tree trunk to the other side where it could not be seen. This behaviour suggests that the observer was perceived as a possible threat to it, i.e. a predator. However it did not take flight like the Crow or most birds that use flight as a means to avoid predators.
The morphology of the Green Woodpecker can throw some light on this behaviour. It has a very large heavy beak which is designed for excavating trees for nests or looking for grubs/insects as food. So that it can grip onto a tree when performing this, it has very large feet and claws so it can grip onto a tree when hammering away at it (Image 2). Overall both of these morphological features mean that flight for the woodpecker is extraordinarily energy consuming in comparison to the Crow of a similar size. As a possible ground predator the observer is not an immediate threat as they must first scale the tree, therefore the woodpecker need not make an instant escape but merely conceal itself.
This behaviour by the Woodpecker represents a perfect example of Optimization Theory in action and the display of a behavioural adaptive mechanism that overrides the constraints of its morphology in this case (Smith 1978). The woodpecker makes use of its morphological adaptation to cling securely to a vertical surface for finding food and shelter. By using a behaviour that overcomes the limitations its evolutionary history has bestowed, it can be suggested that the gene-environment interaction of ancestors (who reacted most efficiently) has been passed to the observed Woodpecker as predisposition to this behaviour. It is also possible that a proximate mechanism is the reason for the behaviour observed, where the Woodpecker in question has learnt itself that it need not immediately escape by flight from a predator and so preserve energy.
An additional suggestion could be that flying away opened up the woodpecker to a greater likelihood of being shot and so only those that assumed an alternative behaviour, when hunting existed, survived. Overall, evolution again displays an optimal behavioural strategy in the Woodpecker, where energy expenditure is pitted against predator threat, leaving the most successful at this balancing act to survive (Krebs 1978).
The Magpie also displays an interesting behaviour that is a consequence of its morphology being adapted for another purpose. Its eyes are on either side of its head giving it almost 360 degree vision at body level. This means it can spot ground predators which ever way it is facing. However predatory birds attack from above, so where the Magpies vision would usually allow it to exert no extra effort in being alert to ground predators, it has developed a regular behaviour of checking above by tilting one eye to the sky, between searching for food on the ground. Thus the Magpie does lose energy and time foraging however this balance is necessary for maintaining its existence, thus making the predisposition for this behaviour selected for, as its participants will be more likely to survive (Krebs 1978). Optimal foraging theory might additionally suggest that the time lapse between checks could be related to how long it might take for a predatory bird to appear and become a threat.
Overall we can see that these species behaviour can be seen as a way of ensuring efficient means of achieving the basic aims and necessities of living. This has been observed here by species adapting the way a specialised morphological feature can be used in multiple scenarios, using behaviour. Additionally it has also been observed that species use behaviour to direct the use of their morphology as energy efficiently as possible across multiple scenarios. Thus behaviour is a way of maintaining an efficient and adaptive lifestyle that can be improved or lost by natural selection.
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Tinbergen, N. (1963). On aims and methods of ethology. Zeitschrift für Tierpsychologie, 20:410-433.
Smith, J. M. (1978). Optimization Theory in Evolution. Annual Reviews: Ecological Systems 9: 31-56.
Stephens, D. W. & Krebs, J. R. (1986) Foraging Theory: Monographs in Behaviour and Ecology. Princeton University Press: U.S.A.
Krebs, J.R. & Davies, N.B. (1978) Behavioural Ecology: An Evolutionary Approach. Blackwell Publishing Ltd: U.S.A.