Download - Biogerographyand ecology of ferns
Biogeography
factors to be considered:
a) size of geographical ranges, and their
spatial placement; b) the way individual
species attain their distribution ranges
(dispersal, extinction and vicariance);
c) the distribution of species numbers
(alpha diversity);
But according to Barrington (1993) that there were three prominent factors relevant to fern biogeography:
a) habitat preferences and distribution;
b) the unique reproductive biology of ferns and
c) long distance dispersal
Ferns are suitable organisms for biogeographic studies because of the following reasons:
a) its worldwide distribution;
b) moderately high but manageable species richness;
and the occurrence of independent gametophytic and
c.) sporophyte generations of ferns, allow direct
comparison of moss-like and angiosperm-like.
Which make them a great model how land plants evolved.
Habitat preferences and Distribution
minute filmy plants whose height might range from 2 mm to 3mm (0.08 to 0.12 inch)
Azolla filiculoides
tree fern in class Polypodiopsida
with an average height of 10 to 25 m.
Geographically ferns are usually found in the tropics, there are only few species could be found in the Arctic and Antarctic regions
A number of families that are exclusive to tropical areas like the:
Marattiaceae , Cyatheaceae,
Blechnaceae Davalliaceae.
Gleicheniaceae,
Schizaeaceae,
Certain genera of ferns could be found in temperate and Arctic regions like the:
Athyrium,
Cystopteris,
Dryopteris and
Polystichum.
Dispersal and Vicariance
Dispersal of ferns species takes place primarily via dust-like spores, but there are species produces gametophytic gemmae for medium dispersal.
Grandstein and van Zanten (2001) had an
experiment on spore dispersal in extreme
environmental condition exposing the spores on
low temperatures and high UV radiation exposure.
Long-distance dispersal of ferns is effective because most ferns have small, lightweight spores that will develop into a gametophyte capable of producing both egg and sperm.
Factors influencing the potential for long distance
dispersal would be the :
- size,
- shape and
- ornamentation of the spores, and
- spores with or without chlorophyll.
Families with Green spores
Some families of ferns which are chlorophyllus such as:
Equisataceae,
Hymenophyllaceae,
Onocleaceae and
Osmundaeceae
Vicariance
Latin word vicaries
derived from vicis means for change,
alternation
vicariance may happen due to continental drift
long time ago that resulted to biogeographic
patterns
Range size: Variability and Spatial Distribution
A. Range size and its correlates
Ferns and lycophytes were geographically widespread in
distribution than the flowering plants due to their efficient spore
dispersal.
But other interpretations have also suggest other factors like :
= age,
= ecological requirements,
= availability of suitable habitats and
= the ability of the species to reach these habitats and survive
Cystopteris fragilis
and that occur almost
throughout temperate
regions and tropical
montane ecosystem.
Lycopodium clavatum
Range size may be also correlated with other reproductive and morphological traits.
Japanese ferns =
ranges are larger in species with multiple
reproductive modes (sexual and vegetative
propagation)
Endemism
FACTORS OF ENDEMISM:
= Geographical isolation – separated by barriers like
mountain, or water
= Abiotic factors (nutrient, temperature, humidity,
elevation)
= Species of different life forms and habitat show
distinct patterns. eg. Epipetric ferns
Alpha Diversity
Alpha diversity refers to the diversity within a particular area or ecosystem and is usually expressed by the number of species in that ecosystem.
A. Pattern of species richness
Marsilea crenata
aquatic fern
B. Mountains as hot spots of biodiversity
Fern diversity among mountain ranges would vary depending on its elevation, because not all mountain ranges had the same elevation.
It has been observed that fern species have been
dependent on humid microhabitats, mild temperatures, in
ravines , streams rather than slopes.
Beta Diversity
Beta diversity is the change of plant or animal communities along ecological gradients.
While these gradients can cover a wide range of
spatial , temporal and ecological aspects, studies on
the beta diversity of ferns have mostly focused on
change in geological substrates and soils as well as
elevation.