How might unfavorable abiotic and biotic factors affect a species?

First, let's define an abiotic and a biotic factor before we involve them with species.

an abiotic factor is a non-living part of an ecosystem (temperature, atmospheric gases, etc.)

a biotic factor is a living thing in an ecosystem (animals, bacteria, etc.)

So how do these things affect a species negatively? Here are some listed examples with descriptions.

abiotic

One huge abiotic factor that is concerning is climate change. Changes in climate, resulting from increased greenhouse gases in the atmosphere, have a big effect on many species. One common example includes the polar ice caps, which are shrinking in size due to increased temperatures, posing a threat to the survival of polar bears.

Perhaps a lesser known concept, but still concerning, is acid rain. When gases like sulphur dioxide are released into the atmosphere react with water and oxygen, they make acid rain. Acid rain is harmful to plants and animals. A common example includes fish populations in lakes/rivers. Acid rain here causes a significant switch in pH levels in the water, a change which many species cannot tolerate.

Finally, natural disasters also contribute to unfavorable effects in various species. This broad idea includes earthquakes, volcanic eruption, wildfires, hurricanes, tsunamis, floods, and more. Since they cannot be foreseen, they are dangerous ranging from the smallest of populations to the largest of ecosystems. Effects are disastrous, the most detrimental being loss of habitat.

biotic

In living factors, a huge threat is, sadly, us. Humans have roamed the world and have brought new species to foreign places, either intentionally or not, and introduced the concept of invasive species. Invasive species may compete for resources and be free of predators, which can cause them to force out a previous species.

Since every living thing must compete for resources, some species may thrive while others suffer, and just the opposite may happen in the course of time. Species are always fighting for food and territory, harming each other in the process. This, however, is not a result of man's doing, and is part of nature.

Some more obvious examples include extreme levels of salinity, lack of water, undesirable pH levels, and more.

Unfavorable abiotic factors (e.g., climate, temperature) and biotic factors (e.g., predators, competition) can impact a species' survival, reproduction, and overall population dynamics.