To solve this problem, we need to identify the process by which detritivores break down detritus into smaller particles. Let's analyze the options:$\newline \bullet$Option 1: Catabolism - This refers to the breakdown of complex molecules into simpler ones within living organisms, releasing energy. It is not specific to detritus breakdown.$\newline \bullet$Option 2: Fragmentation - This is the process of breaking down detritus into smaller particles, which is exactly what detritivores do.$\newline \bullet$Option 3: Humification - This involves the formation of humus from organic matter, a process that occurs after fragmentation.$\newline \bullet$Option 4: Decomposition - This is a broader term that includes the breakdown of organic matter by microorganisms, including both fragmentation and humification.$\newline$Based on the analysis, the correct process by which detritivores break down detritus into smaller particles is Fragmentation.$\newline$Therefore, the correct option is Option 2: Fragmentation.