Conservation of species can take place in their original environment (in-situ) or outside of it (ex-situ).
Examples of ex-situ conservation are zoos and seed banks. Zoos host animals outside of their original environment, under highly controlled conditions. Animals are no longer subject to predation, don’t have to provide for themselves, and have access to advanced healthcare.
Seed banks preserve the starting unit of many plants. Because seeds have evolved to disperse far and wide, either by wind or carried by insects, even excreted by mammals (hello fruit), they are some of the most resistant biological things in the world. They can stay dormant for very long periods of time, and be used to start a plant culture at a later point. Hence, they are a useful ex-situ plant conservation practice.
The main issue with ex-situ conservation is that it neglects the environment. Animals may be sheltered away from the natural environment they evolved in, but unfortunately this means they will no longer be able to survive and live in what would be their original environment.
Similarly, the environment is ever-changing, so unless the animals are there to experience it and adapt accordingly, their abilities would soon fail to match the pressures of a natural environment they might have otherwise been able to thrive in.
Ex-situ can never truly match the right environment, so the biotic-abiotic balance often remains broken once the animal has been detached from its original habitat.
In-situ conservation includes national parks, sanctuaries and reserves which together form protected areas. Other examples include sacred forests and lakes. The aim of in-situ conservation is to protect the original habitat of species with minimal interference and disturbance, so they may continue to thrive in their corresponding space.
Sometimes this includes preventing human expansion and activity such as shooting, or shielding species from predators at critical times to allow their numbers to recover.
Challenges of in-situ conservation include unreliability of various environmental aspects such as natural disasters and changes in environment which can adversely affect the species being protected. The issues are often the reverse of ex-situ conservation.
Ex-situ conservation provides complete control, but this removes the natural parameters that species require, while in-situ conservation provides complete natural parameters that species require, but this removes control.