Question

Discuss how historical factors can influence the distribution of a species (include at least two

distinct ways that are not human caused).

Answer 1

Biogeography can be modified by various historical factors Latitude, Segregation elevation, Sea Level, Migration and Continental Driftetc in which the man has no responsibility.the above phenomenans can be illustrated by various examples like-minded

1.the Roya Valley and in the mountains behind Menton . These locations were defined as foci of endemism, because they harbour a higher number of endemic taxa belonging to the hotspot. The centres of endemism measure (weighted endemism) are also sensitive to the rarity of species in an area, and many widespread species might yield a higher value than a small number of narrowly range‐restricted species (Linder, 2001). For this reason, the Finalese and the upper Var Valley . where some narrowly endemic species (Campanula isophylla and Centaurea jordaniana) are present have to be added to the two previously mentioned areas.

2.While a focus of endemism is defined according to richness only, centres of endemism are characterized by both richness and uniqueness; hence, the centres of endemism partly overlap with both these types of biogeographical entities.

The four areas of endemism identified in this study are mainly located in the Maritime Alps, a portion of the SW Alps that was affected by various palaeogeographical and historical events (Malaroda, 2000; Rosenbaum & Lister, 2005). A glacial sheet covered the area throughout the Quaternary, as geologically demonstrated by the glacial circles found in the Argentera massif area (Federici & Spagnolo, 2004) and by glacial moraine deposits (Malaroda et al., 1970). The patchy ice cover created many potential refugia (Ponel et al., 2001; Ehlers & Gibbard, 2004) mainly in the peripheral zone on the edge of the glacial sheet. The same phenomenon probably took place in the Argentera massif as well, where some relicts of the Tertiary flora like Saxifraga florulenta (Conti & Rutschmann, 2004), Potentilla valderia, and Viola argenteria survived. This is further confirmed by the INDVAL value, showing that these species characterize this area of endemism.

3.The Roya Valley is an area of endemism located in the calcareous bedrocks of the Col de Tende, which separates the Maritime from the Ligurian Alps. It is characterized by calcicole plants, but other taxa are also present and show their distributional limits in this area (e.g. Campanula sabatia, Cytisus ardoinoi, and Campanula fritschii). The variability in substrate and the diversity in habitats and climatic conditions might explain the coexistence of alpine and more thermophilous plant species within a small geographical area. Moreover, being on the edge of the ice sheet, the Roya Valley was a major peripheral refugium where dynamic processes on plant population occurred: divergence (ultimately leading to speciation), migration, or extinction (Hewitt, 1999; Hampe & Petit, 2005). The first event is demonstrated by polyploidy of Primula marginata in south‐eastern populations (Pignatti, 1982) or by the genetic diversity of Gentiana ligustica (Diadema et al., 2005) and Moehringia sedoides (Minuto et al., 2006). Migration and extinction processes might be seen in the fragmented distribution area of some species, such as Primula allionii (Martini et al., 1992). Some species, such as Moehringia lebrunii, probably are relict plants that survived several dramatic historical events (Martini, 1994).

4.The high mountains bordering the Roya Valley in the north and east may have acted as a physical barrier causing the discontinuities and making this the most important suture zone of the Maritime Alps (Kropf et al., 2002; Grassi et al., 2006).

According to INDVAL values, the Finalese area of endemism is mostly characterized by Campanula isophylla. This plant was not influenced by glacial events but its speciation probably dates back to the Cenozoic (Martini, 1982), when an adaptation to the specific substrate present in the area was developed.