Tropical species sensitivity

Tropical species sensitivity

1. Morphological traits

   • Inherently vulnerable to habitat perturbations owing to relatively low population sizes, patchy distributions, poor dispersal abilities, and high habitat specificity
     • Behaviours
       • habitat flexibility seems to aid surviva in fragmented areas (Stouffer & Bierregaard 1995a)
       • nectivorous understory hummingbirds suffered few negative effects from fragmentation because of their abilities to use forest edges and gaps
       • studies show that either frugivores or insectivores or both are more extinction prone than other guilds
       • Species forming mixed-species flocks disappeared more frequently from smaller fragment
         • In addition to mixed-species flocking and army-ant following birds, colonial nesting Icterids may also be vulnerable because they cannot form viable colonies in small fragments (Renjifo 1999).
       • Dispersal
         • A majority of tropical forest bird species have poor dispersal abilities (Terborgh 1974, Bierregaard et al. 1992, but see Terborgh et al. 1997)
         • may depend on morphology (e.g., wing loading) and physiology (e.g., intolerance to sunlight) (Johns 1992).
         • Habitat loss may also disrupt some behaviors of bird species (e.g., mating), thus making them particularly vulnerable to extinction (Reed 1999), but such data are lacking for tropical forest birds.
     • Body size
       • body size is inversely correlated with population size (Pimm et al. 1988), making large-bodied animals particularly vulnerable to environmental perturbation (e.g. Leck 1979, Karr 1982a, Diamond et al. 1987, Christiansen & Pitter 1997, Renjifo 1999, Castelletta et al. 2000)
         • other correlated traits such as large area requirements, greater food intake, high habitat specificity, and low reproductive rates
         • Large bird species are generally more vulnerable to human persecution, whereas small species are generally more vulnerable to habitat loss (Owens & Bennett 2000)
         • body size may be important in early extirpations, but other factors may become more critical as the extinction process proceed
   • lag in time in avian extinctions due to low reproductive effort and high environmental stability

2. Landscape traits

   • DIRECT
     • Existence of refuges can probably dampen the effects of deforestation
     • loss of preferred habitats
       • suitable nesting trees (Van Balen 1999)
     • Whether populations at the edges of their ranges are more vulnerable to deforestation remains unclear (Brooks 2000)
       • because of low densities, populations at the edges of their ranges could be particularly vulnerable to genetic (e.g., inbreeding depression) and/or environmental stresses (e.g., pesticides)
       • Populations may be at their physiological and ecological limits at their distributional edge
         • Nineteen of 29 species at the upper or lower limit of their elevational distributions were extirpated from the western Andes (Kattan et al. 1994)
           • BUT in the Colombian Andes, Renjifo (1999) found that species beyond their usual elevational limits were not disproportionately likely to become extinct, suggesting, in some cases, resilience even at distributionalimits.
         • (Christiansen & Pitter 1997, Gillespie 2001)
     • Extinction proneness can also be affected by the size of a species' range (Ribon et al. 2003)
       • Small ranges may make species more vulnerable to stochastic perturbations
   • INDIRECT
     • Habitat loss may facilitate colonization by invasive species and infiltration by disease vectors and parasites, and it opens up habitats for hunter

3. Introduction stuff

   • Speed of tropical deforestation
   • Globally, one in eight bird species may become extinct over the next 100 years- 99% of the extinctions owing to human activities such as deforestation and hunting (BirdLife International 2000)
   • Ninety-three percent of 902 threatened forest birds are found in the tropics (Birdlife International 2000)

4. Conclusion ideas

   • Extirpation of large predators, superior competitors, pollinators, and seed dispersers may have repercussions for tropical ecosystem functionin

5. Other

   • nest predation by domestic dogs, and death due to pesticides