Introduction to fungal ecological strategiesAll fungi are heterotrophic, which means that they get the energy they need to live from other organisms. Like animals, fungi extract the energy stored in the bonds of organic compounds such as sugar and protein from living or dead organisms. Many of these compounds can also be recycled for further use. Fungi have evolved diverse strategies for obtaining organic (carbon-based) compounds, however. Broadly, fungi are either saprotrophs (saprobes), which decay dead organic matter, or symbionts, which obtain carbon from living organisms. A polypore mushroom is attacked by a parasitic fungus. A few fungi attack small living organisms so aggressively that they have been called carnivorous. Many fungi defy easy categorization, acting as saprotrophs, symbionts, or carnivores at various stages of their life cycles, or in interactions with different organisms. Necrotrophic fungi act both as symbionts and saprotrophs. These fungi infect a living host, which they kill over time, then continue to consume of the dead tissues of the host.