Seed Dispersal Aids Recovery From Disturbance

large bats fly overhead in a forest with a blue sky

Biological Strategy

Tropical rain forest

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Image: Paislie / Pixabay / Free non-commercial use

Manage Disturbance in a Community

When environmental conditions change, they can disrupt an ecosystem’s equilibrium. Excessive rain can cause flooding and drought can cause forest fires. An ecosystem must be resilient to such disturbances. Disturbances are unpredictable in location, size, and intensity, so ecosystems must be able to regrow and must have a variety of duplicate forms, processes, or systems that are dispersed in location. For example, a forest ecosystem can recover from fire because diverse organisms play different roles in different ways and in different locations. Many organisms can resprout or grow from seeds triggered by fire, and their dispersed distribution ensures that an entire population isn’t decimated. Though the recovered ecosystem may look totally different from the pre-fire one, the ecosystem as a whole remains healthy.

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Disperse Seeds

Plants disperse their seeds using a variety of mechanisms, including wind, rain, and attachment to animals. Seed dispersal can be important if plants growing too close together will compete for resources, such as nutrients and sunlight. Since plants are literally rooted in place, seed dispersal is also an important mechanism for expanding their range or reaching new environments.

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Maintain Biodiversity

The greater the amount of genetic and species variation in an ecosystem, the more resilient that ecosystem is to disturbances. Variation in ecosystems across the Earth also contributes to the Earth’s resilience to unpredictable changes. This variation is called biodiversity. Because living systems compete with each other for scarce resources, maintaining biodiversity involves creating conditions for a large variety of species to successfully co-occur and reproduce. For example, within a wetland, there are different vegetation types. This diversity results in a complex mosaic of microenvironments as the vegetation types alter air flows, light regimes, and water temperatures and chemistry. Because organisms vary in their ideal environmental conditions, these micro-environments increase the diversity of plants in the wetland. In turn, having a wetland in an otherwise dry area increases biodiversity at an even larger scale.

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Ecosystems

Eco- ("household"), system ("organized whole")

An ecosystem consists of all the biological and nonbiological elements that make up a defined area. That definition might seem vague, but that means it’s flexible: We can apply the word across different scales and times. Ecosystems can be small, like a single tide pool, or large, like coastal wetlands. Ecosystems can include plants, animals, bacteria, fungi, rocks, temperature, light, soil, and climate—all linked through the flow of energy and cycle of nutrients. Each part of an ecosystem interacts with, and is influenced by, other members of the system. These interactions are dynamic, leading to changes to any ecosystem over time.

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Recovery of tropical rain forests after disturbance depends upon the dispersal of seeds by fruit-eating vertebrates.

“We term this network of species, their dynamic interactions between each other and the environment, and the combination of structures that make reorganization after disturbance possible; the ‘ecological memory’ of the system (21, 22)…The ecological memory is a key component of ecological resilience, i.e. the capacity of the system to absorb disturbances, reorganize, and maintain adaptive capacity (25)…The ecosystem renewal cycle in forests gives rise to a coarse mosaic of patches in different stages of a forest cycle (67), initiated by disturbance and comprising a series of structural phases; commonly recognized are the i) gap (in our terms reorganization), ii) building (exploitation), iii) mature (conservation), and eventually iv) degenerative (release) phases (68, 69)…The gap/reorganization phase is of crucial importance in determining the floristic composition of the entire forest cycle (67). The pattern of reorganization among plants is often dependent on modes of dispersal and the presence or absence of dispersers. In tropical rain forests, vertebrate frugivores are often the main seed vectors (78). In a lowland rain forest in Samoa disturbed by cyclones and fires, seedlings of species dispersed by birds or flying foxes were most abundant in the most severely disturbed area, but this was not the case in less disturbed areas (79). Remnant trees may attract seed-dispersers such as fruit-eating birds and bats (37, 80–82). Vertebrate frugivores can be viewed as keystones in the reorganization phase. In their absence, succession would follow a different trajectory dominated by wind- and passively dispersed plants, and the risk of invasion of wind-dispersed exotic species may increase. In both natural and managed forest landscapes it is essential that ecological memory is maintained.” (Bengtsson et al. 2003:389, 393)

Last Updated August 18, 2016

References

Journal article

Reserves, resilience and dynamic landscapes

Bengtsson, J; Angelstam, P; Elmqvist, T; Emanuelsson, U; Folke, C; Ihse, M; Moberg, F; Nystrom, M

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