An ecological numbers pyramid illustrates population sizes within an ecosystem.. based on the pyramid, which type of organism would be least abundant in most ecosystems? . a) tertiary consumers . b) secondary consumers . c) producers . d) primary consumers .

Based on the pyramid, the organisms that would be least abundant in most ecosystems are THE TERTIARY CONSUMERS.
An ecological pyramid of number refers to a graphical representation which is created to show the number of organisms at each tropic level in a particular ecosystem. The pyramid has the largest size at the bottom and get smaller as the pyramid goes up. The primary producers, which are plants are the ones that are usually found at the bottom of the pyramid and they are normally more than the consumers. Consumers are divided into primary, secondary and the tertiary consumers. The tertiary consumers are usually located at the top of the pyramid and they are often the smallest in number. 

Based on the pyramid, the type of organism that would be less abundant in most ecosystems is : A. Tertiary consumers

Tertiary consumers consist of the carnivores on top of the food pyramid and their number should be significantly  less than the herbivores

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