To solve this problem, we need to identify the causes of biodiversity loss. Let's analyze each cause mentioned in the question:$\newline \bullet$Habitat loss and fragmentation:$\newline$ - This occurs when natural habitats are destroyed or divided into smaller, isolated patches, leading to a decline in species populations.$\newline$ - It is a major cause of biodiversity loss as it reduces the available living space for species.$\newline \bullet$Over-exploitation:$\newline$ - This refers to the excessive use of natural resources, such as hunting, fishing, and logging, beyond sustainable levels.$\newline$ - Over-exploitation can lead to the depletion of species and is a significant factor in biodiversity loss.$\newline \bullet$Alien species invasion:$\newline$ - Alien species, also known as invasive species, are non-native organisms that spread rapidly in new environments.$\newline$ - They can outcompete, prey on, or bring diseases to native species, contributing to biodiversity loss.$\newline \bullet$Co-extinction:$\newline$ - Co-extinction occurs when the extinction of one species leads to the extinction of another species that depends on it.$\newline$ - This is a cascading effect that further contributes to biodiversity loss.$\newline$Based on the analysis, all the causes mentioned are directly related to biodiversity loss.$\newline$Therefore, the correct option is Option 3: Biodiversity loss.