species that often exhibit only few individuals is scarce. And in consequence, the
mechanisms that are responsible for hyperendemism are not well understood.
We here introduce the term hyperendemism which is related to taxa with an
extremely restricted biogeographical range or a very small population size.
Today, the term hyperendemism is used in the context of medicine and diseases
(cf. e.g. Leach 2008). We here advocate using this term also in the context of
biogeography, ecology and nature conservation. With increasing knowledge in
phylogenies, taxa and species distribution and with increasing pressures on natural
populations, there is a growing demand to label species that are likely to be
threatened due to their low abundance and strongly limited area of distribution.
Hyperendemic taxa exhibit an extremely restricted and narrow distribution. It
would be appropriate to define a specific range size for hyperendemics such as one
square kilometre. Dependent on the size of organisms, their life cycle and dispersal
capability, distribution areas of hyperendemics may differ in size. In the case of
mobile animals such as birds, the home range or breeding ground may serve as an
appropriate scale.
For many groups of animals, it is simply impossible to determine exactly their
distribution range as they migrate and the range is more or less flexible. If population
size is small, it may become feasible to record or calculate its number of individuals.
Such small populations may also be spatially restricted, but this is not necessarily the
case. The Javan Rhinoceros (Rhinoceros sondaicus) has been widely distributed in
forests across the island of Java and also in Vietnam but today the population size is
40–60 on Java and maybe 5 in Vietnam (IUCN 2019c).
Thus, we also take species with small populations into account. Since the IUCN
has categorized taxa as critically endangered if the population is smaller than
50 individuals (category CR, criterium D) we adopt this categorization and call the
relating species hyperendemics as well.
The concept of the micro hotspot was most probably introduced by Fenu et al.
(2010). This study focused on vascular plants on the island of Sardinia. Fenu et al.
labelled a mountainous part of the island with a high concentration of endemics as
micro hotspot. Grant and Samways (2011) used the term micro-hotspot for important
subareas in protected areas. They analysed distribution patterns of insects (Odonata)
within a biosphere reserve and distinguished buffer zones, transition zones and
micro-hotspots.
Isolated environments such as springs that are substantially different from their
surrounding habitats serve as habitat islands for endemic species. Hershler et al.
(2015) analysed the assembly of the gastropod fauna of an isolated spring in
southern Nevada. They identified endemism patterns and described a new species
and labelled this spring a micro-hotspot, too. However, in one case there is a gradual
increase of endemism with elevation and in the other case there is a clear limit
between the extraordinary habitat and its surrounding. Nevertheless, in both cases,
those species that share a spatially limited distribution in a micro-hotspot are
restricted to this due to ecological constraints.
The sensitivity of such populations to eradication explains the need of species
conservation management. For this reason, the term micro-hotspot is an adequate
Distribution and Habitat Affinity of Endemic and Threatened Species: Global and. . .
237
mechanisms that are responsible for hyperendemism are not well understood.
We here introduce the term hyperendemism which is related to taxa with an
extremely restricted biogeographical range or a very small population size.
Today, the term hyperendemism is used in the context of medicine and diseases
(cf. e.g. Leach 2008). We here advocate using this term also in the context of
biogeography, ecology and nature conservation. With increasing knowledge in
phylogenies, taxa and species distribution and with increasing pressures on natural
populations, there is a growing demand to label species that are likely to be
threatened due to their low abundance and strongly limited area of distribution.
Hyperendemic taxa exhibit an extremely restricted and narrow distribution. It
would be appropriate to define a specific range size for hyperendemics such as one
square kilometre. Dependent on the size of organisms, their life cycle and dispersal
capability, distribution areas of hyperendemics may differ in size. In the case of
mobile animals such as birds, the home range or breeding ground may serve as an
appropriate scale.
For many groups of animals, it is simply impossible to determine exactly their
distribution range as they migrate and the range is more or less flexible. If population
size is small, it may become feasible to record or calculate its number of individuals.
Such small populations may also be spatially restricted, but this is not necessarily the
case. The Javan Rhinoceros (Rhinoceros sondaicus) has been widely distributed in
forests across the island of Java and also in Vietnam but today the population size is
40–60 on Java and maybe 5 in Vietnam (IUCN 2019c).
Thus, we also take species with small populations into account. Since the IUCN
has categorized taxa as critically endangered if the population is smaller than
50 individuals (category CR, criterium D) we adopt this categorization and call the
relating species hyperendemics as well.
The concept of the micro hotspot was most probably introduced by Fenu et al.
(2010). This study focused on vascular plants on the island of Sardinia. Fenu et al.
labelled a mountainous part of the island with a high concentration of endemics as
micro hotspot. Grant and Samways (2011) used the term micro-hotspot for important
subareas in protected areas. They analysed distribution patterns of insects (Odonata)
within a biosphere reserve and distinguished buffer zones, transition zones and
micro-hotspots.
Isolated environments such as springs that are substantially different from their
surrounding habitats serve as habitat islands for endemic species. Hershler et al.
(2015) analysed the assembly of the gastropod fauna of an isolated spring in
southern Nevada. They identified endemism patterns and described a new species
and labelled this spring a micro-hotspot, too. However, in one case there is a gradual
increase of endemism with elevation and in the other case there is a clear limit
between the extraordinary habitat and its surrounding. Nevertheless, in both cases,
those species that share a spatially limited distribution in a micro-hotspot are
restricted to this due to ecological constraints.
The sensitivity of such populations to eradication explains the need of species
conservation management. For this reason, the term micro-hotspot is an adequate
Distribution and Habitat Affinity of Endemic and Threatened Species: Global and. . .
237