International Journal of Molecular Zoology 2024, Vol.14, No.2, 97-110 http://animalscipublisher.com/index.php/ijmz 105 6.2 Reduced reproductive success Habitat fragmentation can also lead to reduced reproductive success in bird populations. Fragmentation often results in smaller and more isolated patches of habitat, which can negatively impact the breeding success of birds. For example, studies have shown that nest predation and parasitism by cowbirds increase with forest fragmentation, leading to lower reproductive rates in fragmented landscapes. In some cases, the reproductive rates are so low that populations in fragmented habitats become sinks, relying on immigration from more extensive, unfragmented areas to sustain their numbers (Ruiz‐Gutierrez et al., 2008). Additionally, fragmentation can disrupt the breeding activity of birds. Research has indicated that there is less breeding activity and fewer young birds in forest fragments after isolation compared to before isolation (Coddington et al., 2023). This reduction in breeding activity can be attributed to factors such as increased nest predation pressures and reduced recruitment of juveniles. For instance, in the Biological Dynamics of Forest Fragments Project near Manaus, Brazil, the proportion of actively breeding birds significantly decreased after fragment isolation, highlighting the negative impact of fragmentation on reproductive success (Coddington et al., 2023). These reductions in breeding activity and reproductive success can contribute to population declines and increase the risk of extinction in fragmented habitats. 6.3 Vulnerability to environmental changes Bird populations in fragmented habitats are more vulnerable to environmental changes due to their reduced ability to move between habitat patches and adapt to changing conditions. Fragmentation can limit the movements of birds, making it difficult for them to find suitable habitats and resources. For example, studies have shown that landscape composition and configuration influence the movements of forest birds, with open areas acting as barriers to movement (Bélisle et al., 2001). This limited mobility can prevent birds from escaping unfavorable conditions or finding new breeding sites, increasing their vulnerability to environmental changes. Furthermore, habitat fragmentation can lead to smaller home ranges and reduced foraging efficiency, which can negatively impact the physiological condition and reproductive success of birds. For instance, male northern saw-whet owls nesting in fragmented landscapes with low forest cover exhibited higher levels of chronic stress and lower provisioning rates, leading to reduced reproductive success and higher variation in the physiological condition of their young (Hinam and Clair, 2008). These factors can make bird populations in fragmented habitats more susceptible to environmental changes, such as climate change or habitat degradation, further increasing the risk of extinction. 7 Case Studies in Fragmentation Effects 7.1 Case study 1: effects on tropical forest birds Habitat fragmentation has profound effects on tropical forest birds, often leading to population declines and local extinctions. A study conducted in the Usambara Mountains, Tanzania, analyzed 22 years of mark-recapture data to assess how fragmentation influenced survival, recruitment, and realized population growth rate within 22 forest understory bird species. The study found significantly lower apparent survival and realized population growth rates in small fragments compared to larger ones, indicating that fragmentation effects persist long after habitat loss. The depressed demographic rates were observed across various feeding guilds, suggesting that fragmentation sensitivity is not limited to insectivores. The study concluded that future population persistence is uncertain even within large forest fragments in this biodiversity hotspot (Korfanta et al., 2012). Another study focused on the White-ruffed Manakin (Corapipo altera) in southern Costa Rica, where researchers found significant differences in annual adult apparent survival rates between individuals in forest fragments and those in a larger forest reserve. The results indicated that forest fragmentation likely affects population dynamics, putting populations at risk of local extinction despite appearing to persist in fragmented landscapes. The study emphasized the need for conservation actions aimed at identifying and reducing sources of adult mortality to mitigate the effects of fragmentation on tropical birds (Ruiz‐Gutierrez et al., 2008).
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