Final answer:
In a logistic growth curve, the strongest intraspecific competition occurs at the flat part of the curve, reflecting the carrying capacity where resources are limited and population growth stabilizes.
Step-by-step explanation:
The part of the logistic growth curve that indicates where intraspecific competition is strongest is the flat part of the curve where the population size levels off and is not changing size over time. This flat upper line on a growth curve represents the carrying capacity of the environment, which is the maximum population size that can be supported without degrading the habitat. When a population reaches this point, resources such as food, water, and space become limited, leading to increased competition among members of the same species.