(i) Preamble:

This section will introduce you to some of the major kinds of patterns of animal distributions. Our subsequent lectures will discuss the processes that have generated these patterns.

Endemism describes the distribution of a taxon that occurs in one place and one place only, i.e. taxon X is endemic to location Y. Endemism can be variable in scale from a small area (e.g., a species of fish that is endemic to a specific lake) to whole continents.

Provincialism describes the situation where there is congruence among taxa in the degree of endemism in specific areas, i.e. faunal "provinces" (as one manifestation of provincialism) are defined as areas that have high degrees of endemism for a variety of taxa (e.g. fish, birds, insects).

Disjunction describes situations almost the direct opposite of provincialism, i.e., two or more related taxa occurring in widely separated areas (and absent from the intervening area).

While we discuss each separately, you should recognize that each kind of distribution is not necessarily mutually exclusive of the others. For instance, a species can be part of a disjunct distribution within its family, be endemic to a specific area and, along with other taxa endemic to the same area, help characterize provincialism for that area!

(ii) Endemism

Endemism was one of the first patterns described in zoogeography and stems from the fact that islands (the focus of much fascination in zoogeography) typical have high levels of endemism. Australia, for instance, as an island continent has 91% of its mammal fauna as endemic compared to about 19% for the Nearctic and Palearctic together. High endemism on islands is though to result from the high degree of isolation of island habitats from mainland habitats, and hence a high potential for "in situ" evolutionary divergence within island faunas.

Endemism can occur in many forms. First, it is often hierarchical (or nested). A classic example of nested endemism involves the kangaroo rats and pocket mice (Heteromyidae). The figure below shows the distribution of the family as a whole being endemic to southwestern North America, Central America, and extreme northwestern South America. Nested within this broad range, however, the genus Dipodomys is endemic to the western US and NW Mexico. Nested further within the distribution of the family is the distribution of Microsipodops which is found only in the Great Basin Area (Great Salt Lake and nearby areas of Nevada, CA, Arizona).

Endemics can also be classified by their place of origin. Autoendemics evolved in an area within their current distribution. Alloendemics originated somewhere else, dispersed to their current locality, and then subsequently have gone extinct elsewhere. The figure below shows the distribution of the Olympic mudminnow, Novumbra hubbsi, a small fish that is endemic to the Chehalis River valley in western Washington State. This fish is found nowhere else in the world, yet other members of the family occur in Alaska, the eastern USA, and even the Danube River valley in central Europe. The ancestor of this fish probably became isolated in the Chehalis valley and it eventually gave rise to the N. hubbsi.

A good example of alloendemics are generally termed as "relicts", i.e., they are remnants of at at one time much more widely distributed taxon.

Taxonomic relicts are remnants of at one time much more diverse taxa (e.g., more species). A good example is the coelacanth, Latimaria chalumnae, the "living fossil" that was discovered in the 1930's. This is a taxonomic relict of a lineage of early bony fish that were though to have died out over 65 million years ago where 13 genera have been described from fossils (see figure below).

Geographic relicts are taxa that at one time had much wider geographic distributions. Again, fish provide a good example. The figure below shows the distribution of fossils lungfishes (order Lepidosireniformes) as small dots. The larger patches show the extant distribution of the three living families (the South American, African, and Australian lungfishes). Clearly, the current lungfish distribution is only a small remnant of a much wider historical one.

Finally, endemics can be classified as either paleoendemics (those that originated long ago) and neoendemics (endemics of more recent origin). Lungfishes are a good example of paleoendemics as their endemic distribution originated millions of years ago (probably soon after the continents reached their current distribution). Species pairs of threespine sticklebacks (we'll hear lots about these later) are found in only 5 lakes in the central Strait of Georgia region of southwestern BC, despite the fact that the presumed ancestor of these species has a circumboral distribution in the Northern Hemisphere (Japan, Russia, northern Europe, North America). The BC species are thought to have evolved in these lakes after the retreat of glaciers at the end of the most recent glaciation (i.e., no more than 10-15,000 years ago) and are an example of neoendemics.

(iii) Provincialism

The major observation that suggested provincialism to early zoogeographers was that endemic taxa in different groups of organisms tend not to be randomly distributed, but rather tend to co-occur in specific areas. This suggested to people like Sclater and Wallace that different areas acted as distinct "centres of origin" of various taxa and that this explained the co-occurrence of endemic taxa. These different areas of endemism are organized in terms of size from largest to smallest:

Realms (terrestrial versus marine) -----> Regions -----> Subregions -----> Provinces -----> Districts

The best known of these divisions are the six major zoogeographic regions developed by Sclater and Wallace:

Australian, Oriental, African (or Ethiopian), Neotropical, Nearctic, and Palearctic as shown in the figure below.

The development of these regions implies that within a particular group of taxa (say birds or fish), the biotas within each region tend to be more closely related to each other than to similiar taxa in other regions. This is, of course, quite a different concept than the occurrence of similar "life forms" that are not closely related in different biomes that stem from selection in similar environments (i.e., biomes) in different areas of the world.

An important inference from the observation of regional faunas is that they imply that common historical events have shaped the biotas within each area such as common geological, climatological or oceanographic events. Concordance among taxa in endemism is one observation that suggests such commonality. For instance, high degrees of endemism in birds, mammals, etc in Australia suggest a common set of factors have shaped its biota and we know that the long term isolation of Australia from other landmasses has probably driven such endemism in multiple groups.

In addition, nested distributions (genus distributions smaller than family distribution) suggests unique events in specific areas. Clearly, the nested endemism of the rodents discussed in (ii) above suggests a specific set of isolation events to generate a nested pattern of distribution (with each event resulting in the diversification of an even more restricted taxon).

Another manifestation of provincialism is the concept of zoogeographic lines, i.e., "sharp" boundaries marking the transition from one faunal region to another where there is a rapid turnover of biotas.

Of course, "Wallace's Line" is the most famous zoogeographic line and separates the Oriental Region from the Australian Region (see below). On the Oriental side of Wallace's line, there are 28 families of primary freshwater fish. On the Australian side, however, there are only two families. Clearly, the saltwater between the two regions is a powerful dispersal barrier for freshwater fish.

While such lines can vary in their positioning depending on the taxon in question, their broad concordance, again, suggests a common set of historical or contemporary factors regulate species distributions between regions.

Below is an example of such variation. Note how the southern limit of different families of northern (Nearctic) mammals varies (i.e., the positioning of the solid lines). Ditto for the northern distributional limits of different southern families (Neotropical, dashed lines).

The figure below depicts faunal (ichthyofaunal) Provinces and the lines between them for freshwater fish in North America. The values within each province represent the total numbers of families (right) and species (left) and degree of species endemism (below) in each province. Note also how each province tends to follow a major drainage pattern, in fact most are named after the dominating river drainage. "Cascadia" is composed of large rivers draining to the Pacific west of the continental divide - Columbia, Fraser, Skeena rivers. The "Mississippi" Province is dominated by the Mississippi River. Note also that the different provinces differ markedly in their degrees of endemism. The Mississippi Province has 34% endemics, Cascadia 25%, Great Basin 58% compared to the Great Lakes (0.03%), and northern provinces such as Hudson Bay (0%).

Such variation is a classic illustration of the balance between isolation and dispersal between provinces. The provinces north of about 46 N latitude where covered by Pleistocene glaciers and received their current faunas by postglacial dispersal from more southern provinces (e.g. dispersal of Mississippi fauna into the Great Lakes). By contrast, areas like Cascadia contained glacial refugia (the Chehalis and lower Columbia river valleys) and have experienced lots of geomorphologically-based isolation events (e.g., mountain building) that have promoted evolutionary diversification within each province, i.e. endemism.

Click HERE to see a proposed scheme for freshwater provinces (ecoregions) for Canada.

A new scheme proposed by the World Wildlife Federation defines > 400 freshwater ecoregions around the globe (Abell et al. 2008). It permits some nice comparative analyses of global patterns of endemism for fishes.

(iv) Marine provincialism

Provincialism also occurs in the marine realm, although it is usually less well developed owing to the greater interconnectedness of marine habitats and the fact that many marine organisms have life stages that are particularly effective for dispersal (e.g. planktonic larvae in many fish and invertebrates).

Marine provinces for continental shelf areas are shown in the figure below. Such provinces for benthic or epibenthic organisms tend to be generated by the isolating effect of large areas of open ocean that separate continental shelf areas (e.g. between the North American Atlantic Region and Mediterranean Atlantic Region).

Below is a depiction of zoogeographic regions for pelagic fishes. Note that these tend to follow the major temperature zones that we outlined when discussing marine biomes. This is a major difference between provincialism in marine versus terrestrial habitats. The former tend to be associated with abiotic characteristics as opposed to physical isolation and faunas tend to be associated by overriding abiotic constraints on distribution. An example is the amphitropical distributions shown for two cetaceans below. The warmer waters of the subtropical and tropical regions are powerful dispersal barriers for these whales and results in their absence from the tropics. Such temperature-based dispersal limitation may explain why certain taxa, such as some marine fishes, marine birds, and marine mammals, often show high levels of endemism in temperate and Arctic areas.

As a final example of marine provincialism, consider the example of distinct lineages of mitochondrial DNA that were identified in a marine coral. The distinct "northern" and "southern" lineages meet at an apparently sharp boundary in the Java Sea in the southwest Pacific/southeast Indian Ocean (see panel C in the figure below). The meeting area between these distinct lineages may represent an analog of Wallace's Line for a marine species with high dispersal larvae (see Barber et al. 2000). Again, this line may mark the meeting zone of distinct faunas driven by their isolation and diversification in ocean basis that became fragmented when sea levels dropped during the Pleistocene glacial advances.