Birds and Their Role in Seed Dispersal Mechanisms

Seed Dispersal Methods Birds and Their Role in Seed Dispersal Mechanisms Biodiversity is the key to the survival of many ecosystems. Plant dispersal mechanisms play a major role in maintaining the balance within those ecosystems. Herbaceous plants are the key to maintaining a variety of play and animal life. The following will explore seed dispersal mechanisms in three different plant communities. It will focus on the role of birds and the maintenance of plant biodiversity.

Ecosystem are dependent on many different factors in order to survive Theses ecosystems are maintained by the interactions of climatic conditions, vegetative growth, and the number of animals with the community to consume the plants. Seed dispersal is one of the most important of the ecosystem processes. Seed dispersal in depends on animals. It depends on the animal's diet, habitat, numbers, and pattern of movement through the forest (Wescott, 2007).

The length of time that the animal retains the seeds and the pattern of their movement determines plant dispersal in the rain forest. It also depends on whether the landscape is continuous or fragmented. These processes have a dramatic impact on the structure plant and animal communities. Seed dispersal effects the dynamics of the plant and animal communities that live within the area. Monocrop Plant Community Tree plantations in China have been established in China that consist of primarily a single exotic species.

These are typically closed canopy systems established on lands that have been reforested since the 1950s (Elsa et al., 2005). Analysis of understory species composition demonstrated that there were differences in the understory based on the primary species of the planting. The plantings consisted of single species: Acacia confusa, Lophostemon confertus, Melaleuca quinquenervia. The sample also contained some mixed-plantings. It was found that Lophostemon had generally poor native plant colonization when compared to natural forests and other types of plantations (Elsa et al., 2005).

Differences between these plantations was dependent upon pre-existing site conditions. In plantations that were isolated from natural seed sources, native woody plant colonization was poor. Bird dispersed shrubs were the most abundant, while other native woody plants were poorly dispersed (Elsa et al., 2005). Seed availability in degraded tropical landscape suffered significantly in the absence of fauna to disperse seeds (Au, Corlett, & Hau, 2006). Seed availability was found to be the key limiting factor in the establishment of biodiversity in these areas. (Au, Corlett, & Hau, 2006).

Seeds collected with in a grassland sight in China revealed the following seed populations. Plant Type Number of Seeds/Meter Percentage of Total Female Eurya Chinensis Isolated trees Male isolated shrubs All of these seeds appeared to have been dispersed by falling to the ground underneath the plant. In this area, the shrub land revealed a higher total seed count than the forest, with 558 seeds/m2 in the shrub land and 129 seeds/m2 in the forest. The grassland only revealed 47 seeds/m2 (Au, Corlett, & Hau, 2006).

However, there were differences in the number of taxa between these three communities. The shrub land contained the highest number of taxa with 59. This was followed by a community of isolated trees with 42. The forest only contained 42 different species and the grassland contained 9 (Au, Corlett, & Hau, 2006). Birds were suspected to be the primary seed dispersal mechanism in all three communities (Au, Corlett, & Hau, 2006). Less than 1% of the total seeds in these three communities was dispersed by wind. Seed were not dispersed by fruit bats.

In this habitat, seeds were less of a limiting factor than in mono-crop tree plantations. However, in these three communities seed dispersal mechanisms proved to be a limiting factor in seed dispersal. Seed dispersal via the seed rain produced when the plants fruit can account for the spread of local, isolated populations. However, animals or human intervention are often needed to achieve seed dispersal over long distances (Czarnecka, 2005). Hurricanes are also responsible for transport of seeds over long distances (Czarnecka, 2005).

Grasslands were found to consist of a mosaic pattern where dense clusters of a single plant form. This suggests that seed rain around the plant is the primary seed dispersal process at work in these areas (Czarnecka, 2005). Wind may help to spread species to new patches, but the primary seed dispersal mechanism would be likely to be seeds falling to the ground. Compared to brush lands, the dominant species were within the Carex family. The dominant species in the brush lands was Origanum vulgare.

Seed dispersal by anemochore dominated in the grasslands, with nearly 43% of the plants using this methods exclusively. Among brush land plants, dispersal by plants that depended on animals for dispersal, either by eating the fruit or hitchhiking on coats and wings (Czarnecka, 2005). In communities, such as the monocrop plantation discussed earlier, there were few animals to transport seeds for even short distances with in the community. This severely limited the ability of biodiversity to establish in these areas.

Perhaps one of the more surprising results in the study by Au, Corlett, & Hau, (2006) is that there were higher numbers of seeds and a higher number of species in the shrub land. One would expect a forest to have higher numbers. However, this finding supports the importance of birds living in the shrub land as a major contributing source of seeds. A study of the composition and seed dispersal of various plant communities reveals that the presence of animals is important to maintaining diversity in the community.

Seedbanks may be high in areas with few animals to aid dispersal, but birds and other animals play an important part in increasing the number of taxa found with in a community. In a monocrop plantation with few animal species, the seed bank suffered as did the diversity of the area. Plant and animal communities must grow together, when a force disrupts the balance of the community, animals.