A framework for the ecology of arid Australia

We compared characteristics of fish assemblages from Finland and northern Wisconsin on several scales to investigate community-level similarity in environmentally similar but faunistically different small lakes. Although Finland has only half as many fishes in its regional species pool, local species richness did not differ between the two regions. Variability in species composition among assemblages was lower in Finland, suggesting that a large proportion of the fauna could maintain populations across a broad range of environmental conditions, whereas the Wisconsin fauna was composed of more specialized species. Three types of fish assemblages were identified in Wisconsin based on species' presence or absence, whereas on the same scale, Finnish assemblages presented a hierarchical continuum based on species addition. These and other patterns suggest that habitat specialization and the exclusion of small prey species from lakes with piscivores contribute to the occurrence of presence-absence assemblage ty...

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Intercontinental comparison of small-lake fish assemblages: the balance between local and regional processes

Ecological patterns are not only a consequence of adaptive processes, but also influenced by phylogenetic constraints, historical effects, and sorting processes. In contrast to the attention paid to the influence of phylogeny on interspecific ecological patterns, historical effects and sorting processes have been considered less frequently. This article shows that, for the woody flora of western Andalusia, southwestern Spain, these factors may be of substantial importance for explaining covariation among life-history traits (and associated "character syndromes") in plant communities. Multivariate analysis of the covariation across genera of 10 qualitative characters (related to general habit and reproductive biology) revealed a dominant life history-reproductive gradient (called "dimension 1") defining two distinct groups of genera and associated syndromes. Syndromes may largely be explained by reference to historical effects and species sorting processes, without recourse to adaptive explanations. Lineag...

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Historical Effects and Sorting Processes as Explanations for Contemporary Ecological Patterns: Character Syndromes in Mediterranean Woody Plants

There are three major difficulties encountered by those dealing with the phenomenon of endemism: a semantic problem, the absence of a clear conceptual framework, and an analytical problem First, the terms endemic and endemism are used in the literature in unclear or contradictory ways Often neither the title nor the abstract of an article makes the meaning clear Following the usage that tends to prevail among Anglo-American zoogeographers, a species or other taxon is regarded here as endemic to an area if it occurs only in that area To speak of a taxon as endemic in this context without specifying an area is meaningless Since geographic ranges of taxa change with time, time must also be specified, or at least understood Second, a conceptual model is provided in which only changes in ranges (occuring frequently) and speciation (occuring relatively rarely) are seen to change the percentage of endemism in any given area At a subsidiary level, many complex factors influence areographic changes and spec

Area and Endemism

Nutrient-poor soils often support low-stature grasslands, savannas and shrublands where the climate is warm enough and wet enough for closed forests. Though this pattern has long been recognised, the causes are debated and poorly explored. I tested the hypothesis that forest fails to develop where the total nutrient pool is too small to construct both the foliage and the wood. I estimated potential woody biomass from the difference between soil nutrient stocks and forest foliage stocks. Nutrient stocks required for foliage were estimated from leaf tissue concentrations and foliage biomass typical of Amazon forests. Potential wood biomass was estimated from wood nutrient concentrations typical of Amazon forests. Data on soil nutrient stocks were assembled from studies from South American and African forests and savannas and from south-western Australian and south-west African heathlands. According to these calculations, estimated nutrient stocks (kg ha−1) to build a forest would need to be > = P: 20–30, K 200–350, Ca 300–600 and Mg 55–65. Many surface soil horizons from both savanna and heathland sites were below these thresholds. However when deeper soil layers were included, most soils had adequate nutrient stocks. The nutrients in shortest supply were Ca and K and not P. This study suggests that nutrient stocks are usually adequate for constructing the wood needed to build a forest, except where soils are highly leached and very shallow. The implication is that, at steady state, low nutrient stocks seldom constrain forest development. The apparent failure of low nutrient stocks to explain the missing forests on nutrient-poor soils emphasises the need for new ideas on how nutrients, alone or in combination with other factors such as fire, influence vegetation structure.

Do nutrient-poor soils inhibit development of forests? A nutrient stock analysis

No one doubts that ecosystems are strongly influenced by their present-day physical context. Changes along environmental gradients are to be seen all around us. But how important is the long evolutionary history that shaped the biology of component species and led to those components assembling at a particular place? To tackle this question we must compare parts of the world that have similar present-day environments but different histories. Australia is a key laboratory for this natural experiment because much of its biota has had an evolutionary history separate from most other continents, and because it provides a wide range of environments. A variety of aspects of ecosystems have been compared between Australia (Figure 1) and elsewhere. An overview of these comparisons can ask which aspects of ecosystems depend on evolutionary history and which aspects are converAustralia is a key laboratory for this natural experiment

Mark Westoby

Papers

Comparing Australian Ecosystems to Those ElsewhereWhat is the significance of evolutionary history