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In this term paper we will discuss about the impact of micro and macro level climate changes on animal behaviour.
Climate, weather and environment are interconnected and interdependent. As concepts, they are multi-dimensional. Climate is a region’s long-term atmospheric condition typically over decades; while weather is an area’s short term atmospheric conditions, typically over hours or days. The term environment has somewhat different connotation especially from the perspective of animal behaviour.
It implies the kind of habitat in which an animal lives and responds. The animal experiences here the totality of all external factors, both biotic and physical In this sense it is logical to describe environment as the animal’s microhabitat or microclimate, since the environment per se is modified by the animal’s own behavioural choices, more so by its own presence.
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The behaviour of an animal depends upon climate (e.g. annual cycles like migration, hibernation etc.), weather (seeking shades or burrows depending upon high temperature and tide) and its microclimate (top canopy, liter layer etc. where it lives). Change in any component of these systems is bound to affect an animal’s behaviour.
Gross change is quite perceptible, while subtle change brought about by minor change of climate is difficult to notice, until it snow balls into a crisis. The near extinction of many species of birds caused by exposure to organochlorine (OC) insecticides causing shell thinning of eggs is a glaring example of such crisis. Humans have always been intrigued by animal behaviour and the interest has stemmed from both survival need and curiosity about natural world.
Behaviour is centrally important for any species. The survival of a species depends on its individual member’s ability to obtain food and shelter (foraging behaviour), to find appropriate mate and reproduce (reproductive and mating behaviour), to raise offspring and to protect themselves from predators (parental care and anti-predator behaviour).
All such behaviour and strategies ensure survival, and survival in turn ensures evolutionary success. An individual of a species must therefore adopt set of behaviour, some of which are programmed and others are learned.
When a behaviour pattern gets stabilized (through the process of evolution), it repeats itself in a kind of stereotyped pattern, independent of immediate control and learning (e.g. Fixed Action Pattern or FAP).
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The prevailing climate plays an important role in shaping such behaviour; therefore, any change in climatic conditions is bound to influence the behaviour adopted by an animal. An important evidence of evolution is the fossil remains of a species. Unfortunately, behaviour itself does not leave behind any fossil remains. However, many of the fossils of animals indicate kind or change in behaviour subsequent to climate change.
Take for example, the evolution of horse. The fossils of horse lineage in North America indicate that primitive horses were browsers, eating leaves and succulent plants. With climate in North America becoming drier during Miocene, grasslands replaced riparian forests forcing the horses to be fast running and to adopt ability to chew tough grasses.
These behavioural changes are quite evidenced in the change of their foot and tooth structures. The evolution of horse tribe involved progression through eight genera and took some last 60 million years. Indeed evolution is a slow process and so also the corresponding changes in behaviour. However, a strong selection pressure may sometimes act on a population and if generation time is short, there are opportunities to follow changes from one generation to the next.
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Consider for example, Kettlewell’s (1965) well known study on industrial melanism, a kind of mimicry, i.e. change in color in the peppered moth (Biston betularia) brought by local climate change due to industrial revolution in Britain. The preponderant natural population of these moths is light coloured. They are active during night and rest on the lichen infested bark of trees during day remaining camouflaged with lichens, thereby evading predation by the birds.
Pollution, as a fallout of industrial growth, killed the very sensitive lichens, exposing the light coloured moths to their predators; as a result the less predominant darker moths were more likely to survive and reproduce, therefore their frequency in the population increased. Interestingly, as air became cleaner later due to subsequent anti-pollution measures, lichens resurfaced and so also the light coloured moths!
Another example of recent local weather change affecting population and behaviour of animals may be cited from the well-coordinated study of Grant (1981, 1986) on two species of finches living in the Daphne island of Galapagos. Geospiza magnirostris is a bigger bird with relatively large and strong beak enabling it to crack open easily the large and tough fruits like caltrops.
The ground finch G. fortis on the other hand, is smaller with smaller beak and is a seedeater. In 1977-78, a drought prevailed, availability of small seeds become scare and the ground finches failed to breed, their population suffered almost 85 per cent decline. With hard seed and fruits remaining relatively common, G. magnirostris with larger and stronger beaks was favoured and the frequency of these birds increased substantially within a short time.
The situation changed in 1982 when a spate of torrential rain and storm following El Nino, swept Galapagos, the weather eventually leading to a huge excess of small seeded plants. Over next few generations, frequency of smaller bird population increased.
Such effects do not only show the population dynamics pattern as affected by weather conditions, but also the underlying adaptive mechanisms that include behavioural strategies under duress. Indeed studies in behavioural ecology show both the ecological realm of the species under study and the way natural selection might shape the observed behaviour even during periodic climate change.
Behaviour can be divided either into broad descriptive categories (e.g. courtship, nesting, sleeping, feeding, etc.) or into more restricted units e.g. specific patterns shown during various phases of courtship. A chain of events spans these aspects, triggering one action after another.
The physiological and developmental state of the animal is very important in stimulating a specific behavioural action. If any of the physiological or development step is affected by some unwarranted agent or event, the normal physiological or developmental cycles ‘become disturbed, upsetting the chain of expected behaviour pattern.
In recent past many abnormalities or aberrations in behaviour have been noticed, generally caused by change in animal’s microclimate. The episode of eggshell thinning and related problems in birds and other animals caused by tile exposure to organo chlorine insecticides.
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It should be mentioned here that Rachel Carson (1962) in her famous book, ‘Silent Spring’ first described how wide spread use of DDT had caused unusual behaviour like silencing of “robins, catbirds, doves, jays, wrens and scores of bird voices”. Ultimately, DDT and other organo chlorines were banned for agricultural practices in USA and other countries.
An important aspect of physiology directing animal behaviour is its precise regulation by endocrine system. Over years, a finely tuned system of complex interaction between behaviour, hormones and external cues have developed in many animals. Of these, special mention must be made about gonadal hormones viz., androgen, progesterone and estrogen.
Interestingly over species barrier the structure of these steroid hormones remain largely conserved unlike many peptide hormones. Therefore, if the functions of these hormones become affected by some xenobiotics or other chemicals that mimic such hormone action, their effects do not remain restricted to a particular species. Besides controlling aggressive, territorial or mating behaviour, steroid hormones have marked organizational effects during critical period in behavioural development.
Therefore, such effects produce relatively permanent change in the organism’s nervous and other tissues. Thyroid and adrenal hormones also have organizational effects on behaviour. Hypothyroid animal exhibit characteristics of cretinism, slower growth, delayed sexual maturation and retarded development of nervous system.
As a result their actions are slower and occur with great difficulty. Non availability of iodine in the microclimate strongly affects metamorphosis, and/or retention of larval characters in many amphibians (e.g. Axolotol larva). Environmental disruption that may affect iodine content of the soil is bound to affect such susceptible animals.
Since hormones are molecular messengers, precise functioning of the endocrine system via modification of rates and directions of various cellular activities is of fundamental importance to behaviour. A number of endocrine disrupting chemicals (EDCs) like dioxins, polychlorinated biphenyl (PCB), phenolics, pthalates and of course DDT, lindane and other chlorinated insecticides affect microclimate of animals.
Exposure of animals to such xenobiotics early in life may lead to profound and irreversible damage to behaviourally relevant neural circuits, gender development and morphology. The well-known effect of Tributyl tin (TBT) used as anti-fouling paint for oil containers on dog whelk (Nucella sp.) populations in Britain may be cited here. TBT induced development of penis-like organ in the females causing phenotypic sex reversal in these barnacles (“imposex”); as a result the population sex ratio became highly upset.
Similar effects have also been found in fish, alligator and bird exposed to such chemicals. How unsuspecting chemicals might affect key physiological functions like sex differentiation reflected in the behaviour effect, is sometimes beyond imagination! The normal nesting behaviour in birds has been adversely affected by DDT and other organochlorines. Similarly migratory behaviour in Atlantic salmons having high residues of pesticides is adversely affected.
Below is an account of some altered development and reproductive effects caused by hormone-disrupting chemicals (EDCs) invertebrates:
i. Sex reversal – Imposex, female phallus development, abnormal steroid genesis, spermatogenesis and behaviour (salmon, red-eared slider turtle); ovotestis, hermaphrodites (frogs, toads).
ii. Sex reversal – Abnormal penis development, steroid genesis and gene expression (alligator).
iii. Abnormal gonadal differentiation and altered reproductive behaviour (egrets and other birds).
iv. Abnormal genital development, steroid genesis and gene expression (grizzly bear and other mammals).
v. Even humans are not spared from adverse effects of EDCs.
While the above effects generally indicate microclimate alteration affecting fine tuning of precise physiological processes in a particular habitat, projected effects of global climate change on animals is far wide and obviously of much larger scale. There is no doubt that climate change is real and happening now. The average global surface temperature has increased by 0.8°C in the past century and 0.6°C in past three decades largely because of human activities.
If this trend continues, the change could result in an increase in the number of days falling outside of temperature thresholds set by basic physiological tolerance for each species and especially for sensitive species. Amphibians are very sensitive to climate change.
Their populations are declining at an alarming rate even in protected wildlife reserves and parks. The eggs of amphibians have no protective shells to block ultra violet radiation or pollution. Increase in UV caused by reduction of stratospheric ozone can harm young embryos in shallow ponds.
In three of five major reptilian lineages, sex is determined by nest and ambient temperature, since they lack heteromorphic sex chromosome. However, it is just not temperature perse at any particular moment, but cumulative effects of temperature through a critical phase that matter. In the field, the sex ratio of hatchlings is largely affected by location of nests and the thermal microclimate of the nest interior, which in turn depends on the ambient temperature condition.
A two degree overall rise in ambient temperature will affect temperature dependent sex determination (TSD) in reptiles. Similarly old world leaf eating monkeys like colobine will be harder hit by a moderate 2°C rise in global temperature. Already there are signs of subtle behavioral change indicating stress effects in the colobine monkeys.
Some of the observed behavioural changes believed to be induced by global warming are indicated below:
1. Marmots ending their hibernation about three weeks earlier now, compared to thirty years ago.
2. Many fish species are moving northward in search of cooler water.
3. A fruit fly gene normally associated with hot, dry conditions has spread through populations living in traditionally cooler southern regions.
4. Grizzly bears are increasingly moving into areas long been considered as polar bear habitat. The latter are already imperiled by ice loss in the arctic.
Such alteration of behaviour is quite indicative of subtle climate change. It seems that the climate change effect is no more remaining restricted to a particular habitat of an animal, rather it is becoming far wide and on global scale. It is time to wake up. It also needs a knee-jerk reaction for immediate preventive action!
Remarks:
Climate, weather and environment are interconnected. Together and individually they affect animal behaviour. An animal remains fine-tuned to its environment, more so to its microhabitat or microclimate. On daily or seasonal basis the animal responds appropriately to environmental cues for foraging, predation, anti-predation, reproduction, migration, etc.
The survival strategies reflected in their behaviour are product of selection and therefore evolution. Failure in adaptive behaviour during cataclysmic climate change (e.g. glaciation) in the past has resulted in extinction of many species. In recent times a different kind of climate change caused due to anthropogenic activities has become a matter of grave concern. The animals are not adapted to the abruptness or kind of climate change in action and therefore they are not programmed to respond appropriately.
This is leading to mismatching of behaviour, which is quite detrimental for the animal’s well-being and survival Studies of wildlife indicate associations between hormone-disrupting chemicals in the environment and declining population, thinning eggshells, morphologic abnormalities, impaired viability of offspring and neurological disorders including cognitive and neuro-behavioural effects.
An area of grave concern is the EDC-induced sex ratio skew, which has adversely affected behaviour and breeding patterns in wildlife. The projected behavioural effects of global climate change as sequels of global warming are of wide significance – the red alert area include migration, hibernation, reproduction and foraging.
Behaviour is a sentinel of well-being of an animal and of its immediate surroundings. Behaviour also becomes the first casualty of induced weather or climate change. Since climate change is happening, it is high time to recognize the threat of climate change at both macro and microhabitat level and seek preventive measures for survival and well-being of animals.