Geographic Impact on Communities: Videos & Practice Problems

Species diversity in communities is influenced by latitude and area. Generally, species diversity decreases with increasing latitude, particularly away from the equator, due to factors like climate and historical glaciation. Conversely, larger areas support more species due to greater resources and habitats. The island equilibrium model illustrates that species numbers stabilize when immigration equals extinction, influenced by island size and distance from the mainland. Larger, closer islands have higher species richness, while smaller, distant islands experience lower immigration rates and higher extinction rates.

Geographic Impact on Communities

Understanding the geographic impact on communities is essential for grasping how species diversity is influenced by biogeographical factors, particularly latitude and area. Latitude has an inverse relationship with species diversity, meaning that as one moves away from the equator, species diversity typically decreases. This phenomenon can be attributed to several factors. The equatorial region benefits from a climate that promotes biological productivity, supporting a wider range of species. This is largely due to the equator receiving more direct sunlight and higher annual precipitation compared to other latitudes. Additionally, tropical communities are generally older than those at higher latitudes, as glaciation events during ice ages have reset many northern communities, while equatorial regions have had more time for speciation to occur, leading to greater species diversity.

In contrast, area has a directly proportional relationship with species diversity. As the area increases, so does the species diversity. Larger areas provide more resources, habitats, and microhabitats, which can accommodate a broader range of species. Furthermore, larger areas are more likely to be discovered by migrating species, enhancing the potential for greater biodiversity.

Visual representations of these concepts further illustrate the relationships. For instance, a graph depicting species richness for mammals shows that species richness peaks at the equator and declines as one moves toward higher latitudes. Similarly, another graph demonstrates that smaller islands exhibit lower species richness, while larger islands correspond with increased species richness and diversity.

These insights into the effects of latitude and area on species diversity are crucial for understanding ecological dynamics and will be applicable in future discussions on biodiversity and conservation.

Geographic Impact on Communities Example 1

Understanding why tropical communities exhibit greater species diversity compared to those at higher latitudes involves examining several ecological factors. One significant reason is the historical stability of tropical regions, which have experienced fewer glaciation events. This stability has allowed tropical communities to persist longer, providing ample time for evolution and speciation to occur. As a result, these regions have developed a rich variety of species over time.

Additionally, tropical regions benefit from higher levels of precipitation and sunlight, which contribute to increased biological productivity. This enhanced productivity supports a wider array of species, as more resources are available for various organisms to thrive. The combination of these factors—historical stability and favorable climatic conditions—plays a crucial role in fostering the high species diversity observed in tropical communities.

In contrast, misconceptions about tropical ecosystems often arise, such as the belief that they have fewer predators and parasites or that they experience fewer disturbances. In reality, tropical regions are home to a diverse array of predators and parasites, and they can be subject to significant disturbances, including hurricanes and flooding. The intermediate disturbance hypothesis suggests that moderate levels of disturbance can actually promote greater species diversity, further complicating the narrative around stability and diversity in these ecosystems.

In summary, the greater species diversity in tropical communities can be attributed to their longer evolutionary history and favorable environmental conditions, rather than misconceptions about predator presence or disturbance levels.

Which of the following communities would likely have the highest species diversity?

• A. A large island in the tropics.
• B. A small island in the tropics.
• C. A large island in a temperate region.
• D. A small island in a temperate region.

Answer: (A)

What is the Island Equilibrium Model?

The island equilibrium model is a fundamental concept in ecology that describes how the number of species on an island stabilizes over time. This model posits that the equilibrium number of species is reached when the immigration rates of new species arriving on the island equal the local extinction rates of species already present. If a disturbance alters the species count, the ecosystem will gradually return to this equilibrium state.

Two primary factors influence the equilibrium number of species: the size of the island and its distance from the mainland, which serves as the source of species. Larger islands tend to support more species due to their greater availability of resources and diverse habitats, which can accommodate a wider variety of organisms. Additionally, larger islands are more likely to be discovered by migrating species.

Conversely, the distance from the mainland plays a crucial role; islands that are closer to the mainland typically have higher species diversity at equilibrium. This is because proximity increases the likelihood of species migration from the mainland to the island.

Visual representations of the model illustrate these concepts effectively. For instance, as island size decreases or distance from the mainland increases, three significant trends emerge: immigration rates decline, species diversity diminishes, and local extinction rates rise. These trends are depicted through decreasing immigration arrows, fewer species icons, and increasing extinction symbols, respectively.

Importantly, the island equilibrium model is not limited to oceanic islands; it can be applied to any isolated habitat, such as lakes, mountain peaks, or caves. Understanding this model allows ecologists to predict species diversity and extinction patterns in various ecosystems, enhancing our comprehension of biodiversity and conservation efforts.

Geographic Impact on Communities Example 2

In ecological studies, understanding the dynamics of species richness, immigration rates, and extinction rates is crucial for assessing biodiversity on islands. Species richness, represented on the x-axis of the graphs, refers to the total number of species present in a community. The y-axis displays both immigration rates (in blue) and extinction rates (in red), which are essential for determining the equilibrium number of species in a given habitat.

The first graph illustrates that the equilibrium number of species is found at the intersection of the immigration and extinction curves. This concept is further explored in the second graph, which compares large and small islands. It is evident that larger islands support a higher number of species at equilibrium due to their greater availability of resources and habitats, making them more attractive to migrating species from the mainland.

The third graph emphasizes the impact of distance from the mainland on species richness. Islands that are closer to the mainland tend to have a higher equilibrium number of species compared to remote islands. This is because nearshore islands are more accessible to migrating species, which increases their species richness.

When evaluating extinction rates, it is important to note that smaller islands generally experience higher extinction rates than larger ones. Additionally, remote islands, being farther from the mainland, also face increased extinction rates compared to those that are nearshore. Therefore, to identify the scenario with the highest extinction rates, one should look for a small island that is also far from the mainland.

In this context, the correct answer to the posed question is an island that is small and far from the mainland, as indicated by option b. This option aligns with the understanding that both small size and distance from the mainland contribute to elevated extinction rates. Conversely, options that describe small islands near the mainland, large islands near the mainland, or large islands far from the mainland do not maximize extinction rates, making them incorrect choices.

Which of the following graphs best corresponds with a small island that is distant from the mainland?

• A. Graph #1
• B. Graph #2
• C. Graph #3

Answer: (A)

Which of the following statements correctly describes the graph below?

• A. Point A represents a large island close to the mainland.
• B. Point D represents a large island close to the mainland.
• C. Point B represents an island with higher species diversity than point C.
• D. Point D represents an island with higher extinction rate than point A.

Answer: (B)

Here’s what students ask on this topic:

How does latitude affect species diversity in communities?

Latitude has an inverse relationship with species diversity, meaning that species diversity typically decreases as latitude increases, moving away from the equator. This is due to several factors, including climate and historical glaciation events. The equator receives more direct sunlight and higher annual precipitation, fostering greater biological productivity and supporting a wider range of species. Additionally, tropical communities near the equator are older and have had more time for speciation to occur, unlike higher latitude communities that have been reset by glaciation events during ice ages.

What is the island equilibrium model?

The island equilibrium model explains that the number of species on an island reaches a stable equilibrium where immigration rates of new species equal local extinction rates. This equilibrium is influenced by the island's size and its distance from the mainland. Larger islands support more species due to more resources and habitats, and are more likely to be found by migrating species. Islands closer to the mainland also have higher species richness because they are more accessible to migrating species. The model applies to any isolated habitat, not just oceanic islands.

Why do larger areas support more species diversity?

Larger areas support more species diversity because they offer more resources, habitats, and microhabitats, which can sustain a greater range of species. Additionally, larger areas are more likely to be found by migrating species, increasing the chances of species colonization. This directly proportional relationship between area and species diversity means that as the area increases, so does the species richness and diversity.

How does the distance of an island from the mainland affect its species diversity?

The distance of an island from the mainland affects its species diversity by influencing immigration rates. Islands closer to the mainland have higher species richness because they are more accessible to migrating species. Conversely, islands that are farther away experience lower immigration rates and higher local extinction rates, leading to lower species diversity. This relationship is a key component of the island equilibrium model.

What factors contribute to higher species diversity near the equator?

Higher species diversity near the equator is attributed to several factors, including favorable climate conditions, such as more direct sunlight and higher annual precipitation, which foster greater biological productivity. Additionally, tropical communities near the equator are older and have had more time for speciation to occur, unlike higher latitude communities that have been reset by glaciation events during ice ages. These factors collectively support a greater range of species in equatorial regions.