Academic journal article Estonian Journal of Ecology

Substrate Utilization and Feeding Strategies of Mammals: Description and Classification/substraadi Kasutamise Ja Toitumise Strateegiad Imetajatel: Kirjeldamine Ning Klassifikatsioon

Academic journal article Estonian Journal of Ecology

Substrate Utilization and Feeding Strategies of Mammals: Description and Classification/substraadi Kasutamise Ja Toitumise Strateegiad Imetajatel: Kirjeldamine Ning Klassifikatsioon

Article excerpt

INTRODUCTION

It is sometimes the case that the more details of a species' natural history we accumulate, the harder it is to define the ecological essence of that particular species and how it differs from others. For example, the lists of plant species eaten by the common vole (Microtus arvalis) and the striped field mouse (Apodemus agrarius) show considerable overlap, and the more comprehensive these respective lists are, the more similar they become, with both eventually approaching the entire flora of the relevant area. In such a situation the differences between the feeding habits of the two species become unclear. In fact, the two rodents used in this example are very different in their feeding habits, with each tending to consume different parts (either leaf or seeds) of the same plant species. Rather than make a fruitless comparison of food plants, it is perhaps preferable to simply categorize the vole as a herbivore and the field mouse as a granivore. In this way we concisely indicate the feeding strategies of the species concerned. Determination of species' ecological strategies thus enables us to condense ecological information and to express it in evolutionary terms. Indeed, it is nonsense to study evolution from eating plant species A to eating plant species B, while the study of evolution from granivory to herbivory is a meaningful task.

By ecological strategy, a mode of species adaptations to environmental factors (e.g. climatic factors, circadian rhythm, substrate, food, and predators) is meant. The number of strategies used by one species corresponds to the number of environmental factors with which it interacts. The concept of an ecological strategy is largely equivalent to that of specialization, but has a broader meaning. Namely, specialization is the mode by which a species utilizes resources, whereas not all environmental factors that determine ecological strategies are resources; for example, climatic factors or predators.

The names of ecological strategies such as aquatic, terrestrial, arboreal, herbivorous, etc., have been widely used in the zoological literature for a long time (e.g. Osborn, 1902; Eisenberg, 1981; Samuels & Van Valkenburgh, 2008). The most comprehensive treatment of mammalian ecological strategies was provided by John F. Eisenberg (1981), and some further developments were proposed in my earlier works (Miljutin, 1997, 1998). Unfortunately, the process of determining species' ecological strategies is still hampered by methodological difficulties and insufficient development of appropriate typology and nomenclature.

Firstly, there is no stable terminology. Thus, different terms are used for one and the same ecological strategy; for example, 'arboreal' (Eisenberg, 1981) and 'dendrobiont' (Vepsalainen et al., 2008); 'animalivore' (Castro-Luna et al., 2007) and 'faunivore' (Heesy, 2008). Moreover, different meanings are provided to one and the same term. For example, a carnivore is considered as (1) a meat-eater (eating the meat of mammals and birds, e.g. Eisenberg, 1981) or (2) an animal-eater, whose food includes fishes, insects etc. (e.g. 'carnivorous plants' in Juniper et al., 1989). Secondly, the typology of ecological strategies used is frequently logically incorrect. Thus, sometimes a mixture of essentially different terms is used, like 'aquatic and fossorial' (Eisenberg, 1981), instead of 'aquatic and sub- terranean' (habitat) or 'notatorial and fossorial' (locomotion). Furthermore, the terms used are sometimes superfluous. For example, expressions like 'Frugivores/Omnivores, Frugivores/Granivores, Frugivores/Herbivores' (Eisenberg, 1981) indicate on concealed hierarchy: Frugivores (Omnivores, Granivores, Herbivores). Finally, there are no clear criteria for the determination of the ecological strategy of particular species. In other words, it is still unclear how to decide whether an animal is arboreal or not.

In this article I attempt to overcome difficulties described above. …

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