Biologists have tested the hypotheses that communities are...

Name: Problem 9, Chapter 55: Biological Science
Uploaded: 2020-06-19T23:58:00-08:00
Duration: 4 min 13 s
Channel: John Barone
Description: Biologists have tested the hypotheses that communities are highly predictable versus highly unpredictable. State the predictions that these hypotheses make with respect to (a) changes in the distribution of the species in a particular community over time, and (b) the communities that should develop at sites where abiotic conditions are identical. Which hypothesis appears to be more accurate?

Biologists have tested the hypotheses that communities are highly predictable versus highly unpredictable. State the predictions that these hypotheses make with respect to (a) changes in the distribution of the species in a particular community over time, and (b) the communities that should develop at sites where abiotic conditions are identical. Which hypothesis appears to be more accurate?

Key Concepts

Deterministic Community Assembly

This concept posits that species interactions and environmental filters drive community development in a predictable manner. Under deterministic assembly, given stable abiotic conditions, similar communities follow similar successional pathways over time, leading to convergent species distributions regardless of small initial differences.

Stochastic Community Assembly

In contrast, stochastic community assembly emphasizes the role of random events and historical contingencies in shaping community composition. According to this view, chance colonization, extinction events, and unpredictable interactions result in variation in species distribution over time and divergence among communities even in identical abiotic settings.

Ecological Succession

Ecological succession describes the process of change in species composition within an ecosystem through time. It is a key concept for understanding community dynamics because it addresses how patterns of species replacement, influenced by both deterministic and stochastic factors, manifest as predictable or unpredictable trajectories.

Alternative Stable States

This concept explains that ecosystems may settle into different, stable species assemblies under the same environmental conditions. It underscores that, due to historical events or chance differences in initial colonization and interactions, similar sites may develop distinct communities, reflecting a mix of predictable processes and the impact of randomness.

Transcript

00:01 Here we're being asked to evaluate whether or not communities are either highly predictable or at least predictable or whether they are the opposite of this, highly unpredictable.

00:19 So, all right, highly predictable versus highly unpredictable.

00:40 All right.

00:41 And before i forget, let me just note that the answer, although it gets complicated, is highly unpredictable.

00:48 So highly unpredictable is more accurate here.

00:52 And then this question is broken down into two pieces, a and then a b.

00:57 And what we're asked in a is whether or not, in a highly predictable, if species were highly predictable, what their distributions would be like.

01:07 So imagine that we have a mountain side.

01:10 Okay, that's going to be my mountain.

01:12 I will write mountain here.

01:15 And imagine that we census the species of whatever, plants, animals, anything you want, going up the side of the mountain.

01:23 If species are highly predictable, then we'd expect species that live in communities to have similar distributions.

01:30 So each one of these lines represents the distribution of a species along the mountain.

01:35 So if we hiked up the mountain starting here and walked up to here, we'd say, oh, look, these three species all have similar distributions.

01:43 They start the same place in lower elevation, and they go up to this place at a middle elevation.

01:48 And we would see that would be true with other communities along the side of the mountain as well.

01:54 So if you had a highly predictable distribution of species, you'd have clusters of species that had similar ranges or distributions along the mountain.

02:05 If species are highly unpredictable, then those lines would not match up.

02:11 Each species would be, to use the vernacular, doing its own thing...

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