Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

The Theory of Island Biogeography

A heuristic framework for understanding and predicting the distribution and categorical abundance of species in stream communities is presented. The framework requires that species be described in terms of their functional relationships to habitat selective forces or their surrogates, which constitute "filters" occurring at hierarchical landscape scales (ranging from microhabitats to watersheds or basins). Large-scale filters are viewed as causative or mechanistic agents that constrain expression of local selective forces or biotic potential at lower scales. To join a local community, species in a regional pool must possess appropriate functional attributes (species traits) to "pass" through the nested filters. Biotic interactions are also a potential filter on local community composition, and they are invoked at the lower hierarchical levels, after species have passed through the physicochemical habitat filters. Potential landscape filters and their associated selective properties are identified, as are ...

Landscape filters and species traits: Towards mechanistic understanding and prediction in stream ecology

/pdf/playing-chutes-and-ladders-heterogeneity-and-the-relative-4z728lsnhk.pdf

Playing Chutes and Ladders: Heterogeneity and the Relative Roles of Bottom-Up and Top-Down Forces in Natural Communities

The dictionary definition of a law is: "Generalized formulation based on a series of events or processes observed to recur regularly under certain conditions; a widely observable tendency". I argue that ecology has numerous laws in this sense of the word, in the form of widespread, repeatable patterns in nature, but hardly any laws that are universally true. Typically, in other words, ecological patterns and the laws, rules and mechanisms that underpin them are contingent on the organisms involved, and their environment. This contingency is manageable at a relatively simple level of ecological organisation (for example the population dynamics of single and small numbers of species), and re-emerges also in a manageable form in large sets of species, over large spatial scales, or over long time periods, in the form of detail-free statistical patterns - recently called 'macroecology'. The contingency becomes overwhelmingly complicated at intermediate scales, characteristic of community ecology, where there are a large number of case histories, and very little other than weak, fuzzy generalisations. These arguments are illustrated by focusing on examples of typical studies in community ecology, and by way of contrast, on the macroecological relationship that emerges between local species richness and the size of the regional pool of species. The emergent pattern illustrated by local vs regional richness plots is extremely simple, despite the vast number of contingent processes and interactions involved in its generation. To discover general patterns, laws and rules in nature, ecology may need to pay less attention to the 'middle ground' of community ecology, relying less on reductionism and experimental manipulation, but increasing research efforts into macroecology.

/pdf/are-there-general-laws-in-ecology-1230na4894.pdf

Are there general laws in ecology

Stream fish assmemblage data for 34 sites in Wisconsin and Minnesota were obtained from archived sources and were used in conjunction with long—term hydrological data to test the hypothesis that functional organization of fish communities is related to hydrological variability. For each of the 106 species present in the data set, six categories of species traits were derived to describe habitat, trophic, morphologica, and tolerance characteristics. A hierarchical clustering routine was used to identify two functionally similar groups of assemblages defined in terms of species presence/absence. Hydrological factors describing streamflow variability and predictability, as well as frequency and predictability of high flow and low flow extremes, were derived for each of the 34 sites and employed to explain differences among the functionally defined groups. Canonical discriminant analysis revealed that the hydrological data could clearly separate the two ecologically defined groups of assemblages, which were associated with either hydrologically variable streams (high coefficient of variation of daily flows, moderate frequency of spates) or hydrologically stable streams (high predictability of daily flows, stable baseflow conditions). Discriminant functions based on hydrological information classified the 34 fish assemblages into the correct ecological group with 85% accuracy. Assemblages from hydrologically variable sites had generalized feeding strategies, were associated with silt and general substrata, were characterized by slow—velocity species with headwater affinities, and were tolerant to silt. Proportions of species traits present at the 34 sites were regressed against an index of hydrological stability derived from a principal components analysis to test the hypothesis that functional organization of assemblages varied across a gradient of hydrological stability. Results were complementary with the discriminant analysis. Findings were in general agreement with theoretical predictions that variable should support resource generalists while stable habitats should be characterized by a higher proportion of specialist species. Several species of fish were identified as indicative of the variable—stable hydrological gradient among stream sites. A taxonomic analysis showed strong geographic patterns in species composition of the 34 assemblages. However, zoogeographic constraints did not explain the observed relationship between stream hydrology and functional organization of fish assemblages. The strong hydrological—assemblage relations found in the 34 midwestern sites suggest that hydrological factors are significant environmental variables influencing fish assemblage structure, and that hydrological alterations induced by climate change (or other anthropogenic disturbances) could modify stream fish assemblages structure in this region.

https://www.jstor.org/stable/pdfplus/1941217.pdf

Functional Organization of Stream Fish Assemblages in Relation to Hydrological Variability

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...

/pdf/intercontinental-comparison-of-small-lake-fish-assemblages-19coqz9xvi.pdf

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

5 Finnish Game and Fisheries Research Institute, Evo State Fisheries and Aquaculture Research Station, Evo, Finland, SF-16970 Abstract. To evaluate the roles of extinction and isolation in predicting richness and composition of fish assemblages in small forest lakes of Finland and Wisconsin, we analyzed data from 114 Finnish and 55 Wisconsin lakes 0.2-86.9 ha in area. Six isolation variables characterized properties of stream corridors, land barriers, and source pools of invading species; four extinction variables were related to habitat severity, lake area, and productivity. Two types of multivariate analyses were used: the nonparametric classification and re- gression trees (CART) and the parametric linear discriminant analysis (LDA). Both types of analyses showed that extinction variables were collectively more important than isolation variables in predicting richness and composition both in Finland and Wis- consin. We interpret that the greater importance of extinction vs. isolation results, not because isolation is unimportant, but because the probability of an arrival of a new species is much less than that of an extinction. Thus, the time after an extinction event before a subsequent invasion is long relative to the time after an invasion event before a subsequent extinction; consequently, fish assemblages sampled at a given point in time more likely represent the stamp of the extinctions than of the invasions. This conclusion was robust to the differences in the geomorphic settings and fish faunas of Finland and Wisconsin. However, the importance of individual isolation and extinction variables in determining richness and composition differed between the two regions, apparently more from differ- ences in geomorphic settings than from differences in fish faunas. Influences of horizontal rather than vertical barriers over land and water were more apparent in Wisconsin, with its lower relief and higher incidence of lakes without stream connections; influences of the area of the nearest lake (representing the size of the available species pool) and stream gradient were more important in Finland, with its higher relief and higher incidence of lakes with stream connections. The importance of individual extinction variables also dif- fered between the two regions, again reflecting differences in the geomorphic settings of the two lake districts and the strong influence that lake position in the landscape has in determining limnological features of the lake.

/pdf/isolation-vs-extinction-in-the-assembly-of-fishes-in-small-19vo7mq6e3.pdf

Jorma Toivonen

Papers

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

Isolation vs. extinction in the assembly of fishes in small northern lakes

How to consider the effects of time of day, beam strength, and snow cover in ICESat-2 based estimation of boreal forest biomass?