Lecture 3 Rarity Flashcards
(11 cards)
What are the different ways to be rare? (3)
population size
geographic range
Habitat range
if you are rare in one way you also tend to be rare in another
what drives differences in range size?
Evolutionary age
Relative dispersal ability
Niche breadth
Biogeographic accident
what is the correlation between older species and geographical range size?
positive, older species (older evolutionarily) = larger range size.
with younger species they haven’t had time to disperse into their full range, range is expected to increase with time.
Evolutionary age - species have their own ‘type’ of life cycle, what happens?
a species’ range tends to decrease over time as they break into daughter species (population subdivision). So initial decrease but there are more sub-species.
Relative dispersal ability
Species with better dispersal mechanisms have better geographical range e.g. wing loading - wing size relative to body weight
Give a case study regarding relative dispersal ability:
In indo-pacific reef fishes the longer the larval duration = further distance in range (km x 10^3). Also the number of species decreases the higher the mean larval duration in days increases. (Lester & Ruttenburg, 2005).
Larval duration is a convenient surrogate for dispersal potential in marine species that are sedentary as adults and that therefore only experience significant dispersal during their larval phase.
Niche Breadth
wider fundamental niches result in larger ranges (Brown, 1984 ) i.e. Specialists vs. generalists by utilising a greater array of resources and maintaining viable populations within a wider variety of conditions, a species should become more widespread – this would lead to a positive correlation between niche breadth and geographical range size. (Slatyer et al,. 2013) - reference good for niche breadth & geographical range.
what is the best indicator of niche breadth?
temperature, thermal range is the best indicator predictor of latitudinal range extent.
post glacial colonists were the species’ that had a larger temperature range.
who tabled rarity and its different forms?
(Rabinowitz, 1981) most species are rare with limted ranges
biogeographic accident
island endemics should have larger geographic ranges but are limited due to physical barriers in the location they evolved.
what is the difference between a generalist and specialist species?
A generalist species is able to thrive in a wide variety of environmental conditions and can make use of a variety of different resources (for example, a heterotroph with a varied diet). A specialist species can thrive only in a narrow range of environmental conditions or has a limited diet.
