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Describe the different types of species interactions in communities.
Describe the processes that allow some species to coexist in the same habitat by reducing competition.
Explain the positive or negative effect on each species involved in a symbiotic relationship.

A community includes all populations, representing multiple species, in the same region.
An ecosystem consists of the biotic (living community) and abiotic (nonliving environment) components.
Reference: Section 38.1, Figure 37.1

Species interact within communities in various ways, affecting their survival and reproductive success differently.
Types of species interactions include:
- Competition: Harms both participants.
- Mutualism: Benefits both species.
- Commensalism: Benefits one species, while the other is unaffected.
- Parasitism: Harms one species while benefiting the other.
- Herbivory and Predation: Harm one species while benefiting the other.
Refer to Table 38.1 for a summary of species interactions:

Competition occurs when two or more species attempt to obtain the same limited resource.
The consequences of competition are negative for both species since neither can completely satisfy its needs, leading to reduced growth, survival, and reproduction, particularly affecting weaker competitors.
It is theorized that two species cannot coexist indefinitely in the same niche due to this outcome.
Reference: Section 38.1, Figure 38.2

A niche encompasses all resources necessary for an organism's survival, growth, and reproduction.
Each organism has a unique niche, which includes:
- Interactions with other organisms
- Interaction with abiotic environmental factors (e.g., light, water, temperature, salinity, chemicals)
Due to the specificity of niches, two species cannot share the same niche indefinitely without competition.
Reference: Section 38.1, Figure 39.1

According to the competitive exclusion principle, the species that secures more resources will ultimately succeed, leading to the extinction of the less competitive species.
Reference: Section 38.1, Figure 38.3

The example of Balanus barnacles competing with Chthamalus barnacles illustrates competitive exclusion:
- In the absence of Balanus, Chthamalus occupies the entire intertidal zone.
- When Balanus is present, faster growth restricts Chthamalus to the high-tide zone.
Reference: Section 38.1, Figure 38.3

Resource partitioning can occur when multiple species with similar needs coexist in the same habitat by utilizing resources in different ways.
An example includes penguin species in the southern Indian Ocean feeding at different times or locations, thereby reducing competition.
Competitive scenarios can lead to resource partitioning instead of competitive exclusion.
Reference: Section 38.1, Figure 38.4

A graphic representation illustrates various warbler species feeding at different heights in trees, reflecting resource partitioning strategies.

Symbiotic relationships describe interactions where one species typically lives in or on another, often for an extended period.
Three basic types of symbiotic relationships:
- Mutualism: Both species benefit (+/+)
- Commensalism: One benefits and the other is unaffected (+/0)
- Parasitism: One benefits at the expense of the other (+/−)
Refer to Table 38.1 for a summary of species interactions.

In a mutualistic relationship, both partners experience improved fitness.
Example: The relationship between clownfish and anemones, where both species provide protection against predation to each other.
Reference: Section 38.1, Figure 38.5

In commensalism, one species benefits significantly, while the other is not greatly affected.
Example: Mosses growing on tree trunks gain increased sunlight without harming the tree itself.
Reference: Section 38.1, Figure 38.6

In a parasitic relationship, the parasite benefits at the host's expense.
The parasite often feeds on the host but typically does not kill it outright.
Terms:
- The organism that benefits is called a parasite.
- The organism that is harmed is referred to as a host.
Some parasites remain attached to their hosts for most of their lives, while others have complex lifecycles requiring multiple hosts.
Example: Roundworms inside humans, causing a disease called elephantiasis.
Reference: Section 38.1

Herbivores: Organisms that consume plants (e.g., nutria feeding on marshland plants).
Predators: Organisms that eat prey animals (e.g., wolves cooperating to capture elk).
Reference: Section 38.1, Figure 38.8

Coevolution refers to reciprocal evolutionary changes between interacting species due to natural selection.
Necessary conditions for coevolution:
1. Two or more interacting species must exist in the same geographic area at the same time.
2. The interactions of each species must affect the survival or reproduction of the other species, demonstrating reciprocal fitness effects.
Reference: Section 38.1

In the Rocky Mountains, crossbills (birds) eat lodgepole pine seeds.
The crossbills select pine cones with thick, protective scales.
In response, the pine trees that have cones with thicker scales are favored, prompting crossbills to evolve larger, stronger bills.
Reference: Section 38.1, Figure 38.9

In the study area around Grand Teton National Park, the relationship between lodgepole pine and crossbills persists across geographical regions such as Montana and Idaho, indicating interaction dynamics that could guide ecosystem balance.