In what ways is biodiversity threatened?

Happens when the habitat becomes unusable for the species (e.g.: pollution - invasive human activities like mining, agriculture, industry, ... - Habitat fragmentation with the construction of roads).

Effect of habitat fragmentation :

1. Overexploitation

   Overexploitation (hunting, collecting, fishing, ...) already led to species extinction (eg: the dodo, Raphus cucullatus). A secondary effect od overexploitation is that, by decreasing a population size, it can alter the composition and functionality of the entire ecosystem (You can read this article for more information.

   1. Invasive species

      Invasive species can compromise the ecosystem they are introduced in by direct (predation, parasitism, ...) or indirect interactions (reduce habitat quality, changing dynamics of native species ...).
      However, the role of invasive species in species extinction is still discussed (See this article )

      1. Climate change

         Already 5 massive species extinctions occured at the geological time scale. Some of them are due to a sharp climate change.

         Local climate change can also lead to a biodiversity modification in some areas. The change of the environmental conditions will lead to a change in the abiotic factors of the ecosystem. This will have an impact on the whole ecosystem dynamic and can lead to species disparition or apparition.

         Source : M.J. Groom, 2006. Principles of Conservation Biology