This is because toxins are ingested by organisms and accumulate in the fatty tissues. Theses toxins then become more concentrated in successive trophic levels of a food web biological magnification. Magnification occurs because the biomass at any given trophic level is produced from a much larger biomass ingested from the level below and therefore, top-level carnivores tend to be the organisms most severely affected by toxic compounds.
Gizzard
Birds such as chicken, doves and others, and earthworms have gizzard which are responsible for storing and softening the consumed food in their digestive tract. The gizzard serves as the grinder of these food in preparation of the absorptive phase of the G.I tract.
Answer:
Species separated by a physical barrier for a long time, suffer allopatric speciation, so they can not interbreed anymore.
Explanation:
Allopatric speciation consists of the geographic separation of a continuous genetic background giving place to two or more new geographically isolated populations. These separations might be due to migration, extinction of geographically intermediate populations, or geological events. In this speciation, some barriers impede genetic interchange, or genetic flow, as the two new populations that are separated can not get together and mate anymore. These barriers might be geographical or ecological.
Vicariance is the geographical separation of an original population into two or more new groups. Discontinuities in the physical environment like rivers, mountains, water, etc., are physical barriers that impede genetic flow between the separated groups.
The process of allopatric speciation involves different steps:
- The emergence of the barrier.
- Interruption in the genetic interchange
- The occurrence of new mutations and their accumulation in time in each population. Slow and gradual differentiation.
- Genetic divergence by natural selection and reproductive isolation makes it impossible for the two groups to mate even if the barrier disappears.
- Prezigotic isolation mechanisms favored by selection once occurs a secondary contact between the new species in formation.
That is when extinction occurs. Hope I helped!