Towards a Biogeography of North American Charophytes

Abstract

The great bulk of the world’s charophyte literature of the past 100 years or more suffers from several major limitations. Much is entirely descriptive with but few attempts to ascribe any functionality to the features under consideration, or how they adapt such species to their respective ecological niches. Charophyte distributions have been attributed almost entirely to physical parameters with virtually no consideration given to the role of aquatic herbivores or other biotic environmental factors. Furthermore, most workers have focused on relatively restricted areas with little or no reference to others either near or far removed. That there is much to be gained from a wider focus (both spatially and conceptually) that incorporates greater conjecture as well as enhanced collaboration is here suggested. How are the charophyte floras of one region similar to, or different from, those of another, and, of particular significance, ‘Why?’ The authors, being North American, focus on that continent but with the firm conviction that most generalities applicable there hold equally true for other landmasses, and have done so for the previous 10, if not 100, million years. This account focuses first, if somewhat superficially, on 14 widely distinct North American charophyte communities (plus South American Lake Titicaca) and then in greater detail on four of those. Among other issues considered are how species richness relates to latitude; why some geographical entities support more charophyte species than do others; the extent to which charophyte floras reflect the availability of different habitats; the contributions of herbivory to the preceding; the stability of the North American charophyte flora; the ecological considerations most often reflected by charophyte zonation and how–or to what extent–range extensions reflect niche preferences or requirements. While the authors well appreciate just how minimal their efforts may appear a century hence, at least they hope to have placed on the table some considerations with which colleagues from other landmasses may agree, disagree or suggest modifications.

Latitudinal Gradients of Biodiversity: Pattern, Process, Scale, and Synthesis

“…More specifically, higher levels of angiosperm richness existed at warm temperate sites than at tropical sites. Similarly, a tropical peak in richness was absent for North American charophytes (Mann et al 1999). Latitude is also unimportant in determining the number of aquatic macrophytes in Fennoscandia (Virola et al 2001).…”

“…In a small proportion of cases (Figure 3), the relationship between species richness and latitude was nonsignificant (10%; e.g., Bolton 1994, Clarke & Lidgard 2000, Dexter 1992, Dingle et al 2000, Ellingsen & Gray 2002, Mann et al 1999, Oliva 1999, Reid 1994, Poulin 1995, Poulsen & Krabbe 1997, Pysek 1998, Rohde 1999, modal (9%; e.g., Chown et al 1998, Davidowitz & Rosenzweig 1998, France 1992, Janzen 1981, Krystufek & Griffiths 2002, Price et al 1998, Skillen et al 2000, or positive (10%; e.g., Blaylock et al 1998, Hawkins & Compton 1992, Heip et al 1992, Heip & Craeymeersch 1995, Lambshead et al 2000, Rabenold 1979, Santelices & Meneses 2000. Exceptions primarily were associated with (a) narrow latitudinal extents (i.e., a form of scale dependence), (b) species with parasitic life histories, or (c) aquatic floras.…”

Ecosystem services provided by waterbirds

“…This defence effect may also carry over to the community level; in some Swedish archipelagoes species richness of nesting birds is higher on islets with nesting Canada geese than on neighbouring islets without (Fabricius & Norgren, 1987). Mann, Proctor & Taylor (1999) suggested that predation of herbivorous Sveinsson (2013) invertebrates in shallow ponds by shorebirds allows the persistence of charophyte species (e.g. Tolypella glomerata) that lack resistance to herbivory.…”

Charophytes of Insular Newfoundland II: <em>Chara evoluta</em> and <em>Chara canescens</em>

“…On the other hand, the charophyte flora compares favorably numerically with many other parts of northern North America (Mann et al 1999). It is well known that charophytes are rapid early colonizers of disturbed habitats (Olsen 1944) suggesting that dispersal is not a significant limiting factor for this group, especially within a single land mass.…”

“…in Lois. and these were added to the list for Insular Newfoundland (Mann 1998(Mann , 2000Mann et al 1999). A search of saline coastal lagoons and estuaries on the southwest coast of Newfoundland identified several more sites for C. evoluta, but no more for C. canescens.…”