International Journal of Molecular Zoology 2024, Vol.14, No.2, 97-110 http://animalscipublisher.com/index.php/ijmz 99 3 Causes of Habitat Fragmentation 3.1 Natural causes Natural causes of habitat fragmentation include geological and climatic events that alter the landscape over time. Volcanic activity, for instance, can create isolated forest fragments, as observed in Hawaiian forests where volcanic eruptions 153 years ago led to the formation of distinct forest patches. These patches vary in size and structural features, which in turn affect the richness of native and exotic bird species. Smaller fragments tend to be dominated by native species, while larger fragments host a mix of native and exotic species, demonstrating the long-term ecological impacts of natural fragmentation events (Flaspohler et al., 2010). Additionally, natural disturbances such as wildfires, hurricanes, and landslides can lead to habitat fragmentation. These events can create a mosaic of habitat patches with varying degrees of connectivity and quality. For example, in the western United States, natural disturbances are common in forested landscapes, and their interaction with anthropogenic fragmentation can influence bird populations differently compared to more stable regions. In these dynamic environments, natural predators and other ecological factors play a significant role in shaping bird community responses to fragmentation. 3.2 Human-induced causes Human activities are a major driver of habitat fragmentation, often resulting in more severe and widespread impacts compared to natural causes. Deforestation for agriculture, urban development, and infrastructure projects leads to the creation of isolated habitat patches. In the Brazilian Atlantic forest, for instance, human-induced fragmentation has significantly affected bird species, with certain species showing marked declines in fragmented habitats compared to continuous forests. This highlights the need for conservation strategies that consider species-specific responses to human disturbances (Anjos et al., 2011). Moreover, habitat fragmentation due to human activities can disrupt ecological processes and lead to population declines. In the midwestern United States, forest fragmentation has been linked to increased nest predation and parasitism, resulting in lower reproductive success for migratory birds. This suggests that fragmented landscapes may act as population sinks, relying on immigration from more intact habitats to sustain bird populations. Conservation efforts should focus on preserving large, unfragmented core areas to mitigate these negative effects (Coddington et al., 2023). 3.3 Global patterns of fragmentation Globally, habitat fragmentation exhibits distinct patterns influenced by both natural and human-induced factors. Tropical regions, in particular, are highly sensitive to fragmentation, with significant impacts on bird species and ecosystem functions. A study spanning five continents found that tropical bird communities are more severely affected by fragmentation compared to temperate regions. Insectivores and large frugivores, for example, show a marked decline in fragmented tropical habitats, which can disrupt key ecological processes such as seed dispersal and insect herbivore control (Bregman et al., 2014). In contrast, temperate regions may exhibit more resilience to fragmentation, with less pronounced impacts on bird community structure. However, even in these regions, fragmentation can lead to long-term demographic changes. In the Usambara Mountains of Tanzania, long-term studies have shown that fragmentation reduces survival and population growth rates for various bird species, indicating that the effects of fragmentation can persist long after the initial habitat loss. This underscores the importance of considering both immediate and long-term impacts of fragmentation in conservation planning (Korfanta et al., 2012). 4 Behavioral Changes in Birds due to Habitat Fragmentation 4.1 Altered migration patterns Habitat fragmentation significantly impacts the migration patterns of birds. Fragmented landscapes often create barriers that disrupt traditional migratory routes, forcing birds to alter their paths. This can lead to increased energy expenditure and higher mortality rates during migration. For instance, studies have shown that birds from fragmented landscapes exhibit higher resistance to boundary-crossing and increased dispersal success compared to
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