Tuesday, 14 July 2020

A GRASS MENAGERIE: II - The Inhabitants of the Grasslands



In essence, the smaller denizens of the grasslands (including the myriad of insects inhabiting this biome) live in a forest-like environment – not under a canopy of leaves and between tree trunks, but rather between the culms and the inflorescences of the taller grasses. Their environment is dense and provides for ample opportunities either to shelter or to escape from predators. 


This image is Copyrighted © Berndt Weissenbacher/BeKaHaWe. If you like it, you may share this image as presented here under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License (CC BY-NC-ND 3.0). NO OTHER USE OF THIS IMAGE is permitted without the express consent of the photographer.


Moreover, these smaller organisms, experience subtle stratification of the environmental factors (such as light intensity, temperature and humidity) from ground level upwards to the top layer of the grasses. These littlies can move up and down in their environment to modify, albeit very slightly, the influence on their tiny bodies of a few environmental factors. For example, any small motile animals living in the grasslands can escape the heat of a summer’s day by moving down to the shaded ground level; they can escape desiccating winds, again by sheltering at the bases of the grasses. Despite these advantages, the differences between day and night are significant and can prove to be challenging to the small inhabitants; at night the grasslands become much colder, as a lot of heat is re-radiated to outer space, while far less heat is trapped in the sparse biomass of the vegetation. Of course, for the larger animals the grasslands are essentially two-dimensional environments, with the subtle changes in environmental conditions proving insignificant (apart from changes from day to night).


This image is Copyrighted © Berndt Weissenbacher/BeKaHaWe. If you like it, you may share this image as presented here under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License (CC BY-NC-ND 3.0). NO OTHER USE OF THIS IMAGE is permitted without the express consent of the photographer.


For many animal species, the grasslands become uninhabitable during the winter seasons. In general, two responses have evolved to this challenge. Those motile organisms that can not cope with the prolonged dry, cold times will migrate to areas that are more amenable in environmental conditions. The larger herbivores often partake in long-distance migrations, following the patchy and intermittent rainfall. Many bird species are trans-equatorial migrants, using long-distance flight to inhabit grasslands only during the wetter summer months in both hemispheres.


This image is Copyrighted © Berndt Weissenbacher/BeKaHaWe. If you like it, you may share this image as presented here under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License (CC BY-NC-ND 3.0). NO OTHER USE OF THIS IMAGE is permitted without the express consent of the photographer.


Many of the smaller organisms that are not able to escape from the rigours of the winter season by migration over large distances enter a period of dormancy, often for significant stretches of time. In regions of the planet with warmer climates, many insects living exclusively in grasslands aestivate during the most arid months. Populations of active insects will fluctuate in number seasonally; moreover, the occurrence of large, stable populations of insects in local areas of grasslands tends to be less predictable than in other biomes. A number of insect taxa do cope well with the environmental conditions in grasslands. These include orders of insects such as the Orthoptera (including grasshoppers and locusts) and the Hymenoptera (including ants). The very successful insects consume the leaves of grasses themselves, or they harvest, store and consume the grass seeds.


This image is Copyrighted © Berndt Weissenbacher/BeKaHaWe. If you like it, you may share this image as presented here under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License (CC BY-NC-ND 3.0). NO OTHER USE OF THIS IMAGE is permitted without the express consent of the photographer.


For the much larger vertebrate herbivores that inhabit the grasslands, food is present in abundance, provided the animals can graze the grasses themselves, feed on the grass seeds or select the herbs nestling deeper down between the grasses. Although the biodiversity of grassland plants is generally very high, the vegetation types available for herbivores is limited to grasses and smaller, usually non-woody flowering plants that grow here. Consequently, the diversity of animal life that is supported by grasslands is impoverished (in general) when compared to other biomes like the woodlands and forests, at least in terms of the number of species that inhabit the grasslands. This is not necessarily the case in terms of the number of individuals that live in the grasslands, since adaptation to this periodic environment has occurred in many groups of organisms (such as the grasses themselves, and the flock-forming seed-eating birds and the herd-forming grazing antelopes).


This image is Copyrighted © Berndt Weissenbacher/BeKaHaWe. If you like it, you may share this image as presented here under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License (CC BY-NC-ND 3.0). NO OTHER USE OF THIS IMAGE is permitted without the express consent of the photographer.


Amongst the numerous antelope species living in grasslands and open savannas, an interesting correlation exists between the size of individuals of a species and the social behaviour that has evolved in that species. The smaller browsers and grazers require vegetable food sources of high nutritional quality. Their bodies have a small volume compared to their surface area. To keep fuelling the high rate of cellular respiration required to maintain a constant and high core body temperature, these small antelope must be highly selective in the food that they consume. Therefore, small antelope species are solitary or live in small family groups.


This image is Copyrighted © Berndt Weissenbacher/BeKaHaWe. If you like it, you may share this image as presented here under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License (CC BY-NC-ND 3.0). NO OTHER USE OF THIS IMAGE is permitted without the express consent of the photographer.


In the much bigger herbivores, the quality of the food is not that vital. Inherent in the large size is a decreased ratio between the surface area of the organism and its volume that allows for a slower basal metabolic rate than that found in smaller species. With a small surface area compared to volume, large organisms are not faced with excessive heat loss through their skin. At the same time, the larger volume allows for the digestion of the food to proceed at a slower pace. Large antelope can graze grasses and allow the digestion to take place over time; hence the evolution of multi-chambered stomachs and the behaviour of chewing the cud in the antelope species. The alternative strategy, seen in horses and zebras, for example, involves the evolution of a large caecum; in essence, this is a spacious storage vat in the hindgut in which vegetation can be decomposed by bacterial action. Whatever the anatomy of these larger herbivores, they can survive easily in vast herds since the food they consume is more easily available, albeit of low nutritional value.


This image is Copyrighted © Berndt Weissenbacher/BeKaHaWe. If you like it, you may share this image as presented here under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License (CC BY-NC-ND 3.0). NO OTHER USE OF THIS IMAGE is permitted without the express consent of the photographer.


Add to this another benefit: the relatively low height of the grassland vegetation allows for vigilance against predators for the larger animal species. Living in a large group means more eyes and ears, as well as a smaller chance that a particular attack by predators will result in the death of any one of the members of the group. (Of course, one of us will die, but the chance of it being I is lessened in a large group.) The ability to live in larger herds has necessitated some form of herd co-operation and control that is complex enough to promote social cohesion, especially during courtship and mating. So vast herds of large grazers occupy the grassland environment, tracking the intermittent rainfall in spectacular long-distance migrations. Their predators, too, follow the migrations, but to a lesser extent – territoriality between carnivores well-equipped with the weapons of their trade can be intense and will limit the movement of groups of predators.


This image is Copyrighted © Berndt Weissenbacher/BeKaHaWe. If you like it, you may share this image as presented here under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License (CC BY-NC-ND 3.0). NO OTHER USE OF THIS IMAGE is permitted without the express consent of the photographer.


Another feature vital for the survival of mammalian herbivores in grasslands is the production of precocial young, that is, babies that are fully functional very soon after birth. The gestation periods of grassland herbivores is lengthened, in general, and the newborn is able to be on its feet and run with the herd within minutes after birth. In the smaller herbivores, where no herd behaviour is found, the young are precocial nevertheless, although they will often hide in denser vegetation or denser patches of grassland near where the mother is feeding.


This image is Copyrighted © Berndt Weissenbacher/BeKaHaWe. If you like it, you may share this image as presented here under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License (CC BY-NC-ND 3.0). NO OTHER USE OF THIS IMAGE is permitted without the express consent of the photographer.


The lack of tall vegetation in which predators can conceal themselves has necessitated the evolution of larger carnivores that can run down their prey, rather than relying on concealment and a pounce at close quarters. Three strategies in hunting prey among the larger carnivores prevail in grasslands: sheer speed of pursuit, endurance of long-distance chasers or the use of elaborate hunting strategies in larger social units of predators. Predators that rely only on speed still live either as solitary individuals or in small family groups, usually a female and her offspring only. This is often not the case with the two other groups – the long-distance chasers and the strategic hunters both require the co-operation of several members of the group in order to kill prey. This interdependence of members of a group for effective hunting goes hand in hand with more complex and elaborate social behaviour. Maintaining co-operation in a pack or pride requires social interactions that promote group cohesion, such as appeasement behaviours and social ranking of individuals within the group. Invariably, a hierarchical social system develops in these predatory species.


This image is Copyrighted © Berndt Weissenbacher/BeKaHaWe. If you like it, you may share this image as presented here under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License (CC BY-NC-ND 3.0). NO OTHER USE OF THIS IMAGE is permitted without the express consent of the photographer.


For the rodents, the omnivores and the smaller carnivores of the grasslands, shelter from the harsh environment, concealment from predators, or safety during reproduction is often found in burrows. The grassland environment, with its relatively deep soils and the top layer of the soil knitted together by the adventitious root systems of the grasses allows deep tunnel systems to be excavated by many animals that have the strength and the equipment (such as large claws) to do so. Subsequent occupation of the burrows by a host of other species – comprising individuals that themselves can not dig effectively – means that these tunnel systems often stay in use for long periods.


This image is Copyrighted © Berndt Weissenbacher/BeKaHaWe. If you like it, you may share this image as presented here under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License (CC BY-NC-ND 3.0). NO OTHER USE OF THIS IMAGE is permitted without the express consent of the photographer.


Photographing wildlife in grasslands is challenging. The larger species (mammals and birds) will flee readily and they can not be approached without difficulty. The unpredictability of the occurrence in any specific area of larger animal species can be taxing too. For me, portraying the grasslands has remained a test that I accept with glee. To display the magnificence of this biome and its menagerie of inhabitants will remain a special privilege always – particularly so since I too am an original inhabitant of the Highveld’s grasslands.

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