Locusts (grasshoppers in the family Acrididae) undergo...

Locusts (grasshoppers in the family Acrididae) undergo cyclic population outbreaks. Of the mechanisms of density-dependent regulation shown in Figure $53.18,$ choose the two that you think most apply to locust swarms, and explain why.

Key Concepts

Disease Transmission

In population ecology, disease transmission is a key density?dependent mechanism whereby individuals in a dense population are more likely to come into close contact with one another, facilitating the spread of pathogens. As infectious diseases spread more rapidly in crowded populations, there is an increase in mortality rates which in turn helps regulate the overall population size, contributing to cyclic fluctuations in population outbreaks.

Competition for Limited Resources

Competition for limited resources is another density?dependent factor that becomes more intense as population density increases. In a high-density setting, individuals must compete more fiercely for essential resources such as food and shelter. This intraspecific competition can lead to reduced growth, lower reproductive rates, and increased mortality, thereby limiting population growth and contributing to the regulation of cyclic population outbreaks.

Transcript

00:02 Okay, so we are talking about density dependent regulation and locusts.

00:15 Okay.

00:17 So first let's talk about locusts.

00:19 They are taxonomically the same as grasshoppers.

00:23 So the thing that distinguishes between grasshoppers and locust is the swarming behavior.

00:32 So we have grasshoppers.

00:37 So they're taxonomically the same.

00:46 But we see swarming in locusts and we see solitary behavior in grasshoppers.

00:58 So there's a morphological and a behavioral change from the grasshopper.

01:05 Again, it's normally solitary to the grouping and swarming behavior.

01:09 And that's when they're called locusts.

01:12 So we see a behavioral and morphological change.

01:24 And that leads us to the swarming behavior of the locusts.

01:28 And the changes that we see in the morphology and physiology are attributed to shifts in environmental condition.

01:36 And this could be from rain or some other change in the environment that causes a physical and behavioral change so that the grasshoppers become more abundant.

01:51 So the reproductive output increases and they become more attractive.

01:54 To being in groups.

01:56 And the swarming behavior is actually a response to increased abundance in these groups.

02:03 So we see morphological and physiological changes because of this increased physical contact that they have with each other in these large groups.

02:13 And that causes them to release more serotonin, which promotes the swarming behavior.

02:18 So we see increased touching in the groups, increases serotonin.

02:26 And that increases swarming.

02:32 And that's when we get these locusts that swarm in these large groups and in very concentrated areas...

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