种内竞争，亦称种内斗争，指同种生物个体之间的生存竞争，达尔文认为同种生物由于要求相同的生活条件，竞争是最激烈的，提出种内竟争是自然选择的重要基础。

例如争取食物来源、争取地盘或是交配机会。如蚱蜢，一群蚱蜢中的各个个体取食同样的食物，虽然互不干扰，但每一个个体都对其他个体的取食造成负面影响。

种内竞争对群体的数量也有很大影响，如果群体密度过大，种内竞争会变得非常激烈，有限的食物只能允许最能适应的个体存活，雄性间的竞争使得只有最强壮的才能生育后代。

Intraspecific competition is an interaction in population ecology, whereby members of the same species compete for limited resources. This leads to a reduction in fitness for both individuals. By contrast, interspecific competition occurs when members of different species compete for a shared resource. Members of the same species have very similar resources requirements whereas different species have a smaller contested resource overlap, resulting in intraspecific competition generally being a stronger force than interspecific competition.