The zürich-montpellier school of phytosociology

In many field investigations some method of sampling vegetation must be employed to procure data from which can be made computations of the abundance and importance of species. The method should be both accurate and easy to use. The methods generally used in the past have been lacking in one or the other of these characteristics. The easiest and least accurate method of ascertaining the relative importance of the several species in a plant community is by ocular estimation, which is merely making the best guess possible. The quantitative relations among the species are sometimes expressed by assigning them to abundance classes described by such terms as: very rare, rare, infrequent, locally frequent, scarce, sparse, occasional, scattered, common, copious, locally abundant, moderately abundant, abundant, moderately dense, dense and dominant. When these terms are not standardized, the assigning of species to such classes is highly subjective and the method often lacks the exactness necessary for scientific analysis. There are various methods of determining the quantitative relations among the species of a community. Most of these are based on the examination of samples, located either at random or along definite lines through the area studied. The measurements of the vegetation in these samples are tabulated and abundance or other

The Statistical Analysis of Chaparral and Other Plant Communities by Means of Transect Samples

Eggs and three different stages of premetamorphic tadpoles of moor frog Rana arvalis and common toad Bufo bufo were offered to the following potential predators in acidified lakes: newt Triturus vulgaris, water beetles Rhantus exoletus and Dytiscus lapponicus, dragonfly larvae Leucorrhinia dubia and Aeshna spp., water boatman Notonecta glauca and water bugs, Cymatia bonsdorffi, Glaenocorisa p. propinqua, and Corixa dentipes.

The predation pressure on eggs of R. arvalis was low due to thick jelly. The eggs of B. bufo were not attractive to predators with chewing mouth parts due to unpalatability but predators with sucking mouth parts were not repulsed. Tadpoles of R. arvalis were eaten by all predators but tadpoles of B. bufo were unpalatable to most predators. The predators used in the experiments are the new top predators in acidified fishless lakes. They may contribute to the reduction of populations of R. arvalis in acidified areas.

https://www.jstor.org/stable/info/3682503

Predation on amphibian eggs and tadpoles by common predators in acidified lakes

1. When assessing the cause of population absence or decline, it is important to understand the relative effect of local, regional and global factors. In this study we evaluated the first of these factors for two frog populations. 2. Amphibians are often absent from intensively farmed areas. There could be several reasons for this, one of them being the quality of the aquatic habitat available for reproduction. 3. In order to test why common frogs Rana temporaria and moor frogs Rana arvalis are absent from most ponds in the intensively agricultural areas of southern Sweden, we performed a field experiment. Spawn of both species were introduced into 18 ponds surrounded by intensively cropped fields. 4. Tadpole performance generally did not differ from that in a set of reference ponds in various other habitat types where one or both of these frog species occurs naturally. 5. In the same experimental ponds and in a number of reference ponds, we also introduced tadpoles of the two species into enclosures that protected them from predation and thus increased recapture rate. This experiment revealed that the water quality of farmland ponds is rarely unsuitable for successful frog reproduction. 6. Having measured abiotic and biotic variables in the experimental and reference ponds, we assessed the importance of different parameters to tadpole performance. While farmland ponds generally had higher pH, higher conductivity and higher nitrate and nitrite concentrations than our reference ponds, these factors had no discernible effects on tadpole performance under the ranges found across all pond types. None of the other parameters differed between the two groups of ponds, nor did they have any strong or obvious effects on tadpole performance or survival. 7. Synthesis and applications. The results indicate that water quality alone is not responsible for the scarcity of amphibians in farmland areas of southern Sweden. To understand better the cause of their rarity, future studies should also focus on the quality of the terrestrial habitat surrounding the ponds and the metapopulation structure. (Less)

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Does pond quality limit frogs Rana arvalis and Rana temporaria in agricultural landscapes? A field experiment

This paper has been limited chiefly to a discussion of the nature of the characteristics that are classified under the category of floristics and structure of the community. Methods of studying these characteristics and applications of the methods in grassland research have been described and evaluated. The four other categories of community characteristics, namely, environmental relations, geographic distribution, plant succession and processes involved, and classification are not considered in detail. The choice of characteristics to measure and the methods to employ depend primarily upon the purpose of the study and secondarily upon the time, equipment, assistance,etc., that can be made available. For a full understanding of a community all the characteristics must be studied. Grassland ecology will be advanced by careful consideration of all basic principles and characteristics of vegetation and by the use of methods that have yielded results or by the development of new methods.

Ecology of the Grassland

Plant ecology is the study of plants in their relation to environment. It embodies, on the one hand, the determination of certain facts; on the other, the interpretation of these facts in the light of certain natural laws and principles. The plants supply one set of facts; the environment another. The completeness with which we may hope to coordinate the two depends (I) upon the completeness with which we are able to determine the facts; (2) upon the extent of our knowledge concerning the laws and principles involved; and (3) upon our ability to correctly evaluate the facts in relation to the laws and principles. To a very considerable degree the characteristics of vegetation, as it exists today, are a product of environmental conditions which no longer exist. From this point of view, they must be studied in the light of facts which no longer are susceptible to direct observation. On the other hand, the very presence of these characteristics, as we see them today, is dependent upon the presence of environmental conditions which favor or at any rate permit their existence. It would seem a logical deduction, therefore, that in studying any particular piece of vegetation, from an ecological point of view, our first step must be to determine the facts as they exist on the ground: facts regarding the vegetation, on the one hand; facts regarding the habitat, on the other. And if there is any one set of facts which is more susceptible to direct study and exact characterization than any other, it is the floristic composition of the vegetation.

G. E. Nichols

Papers

Methods in the Floristic Study of Vegetation