Posted by: oikosasa | March 15, 2013

Guess who planted invasive seeds on blackbuck mating territories?

To consider at your Friday dinner tonight: Sex-biased diets affect the ecology of other species in the surroundings. Read more in the new early View paper “Antelope mating strategies facilitate invasion of grasslands by a woody weed” by Shivani Jadeja and colleagues. To get a good feeling of the antelope and the seeds that the males eat, read Shivani’s beautiful description of the wildlife reserve in western India, in her summary of the paper:

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Mesquite (Prosopis juliflora) pods

In Velavadar National Park, a grassland wildlife reserve in western India, invasive mesquite trees (Prosopis juliflora) obstruct the horizon, where the land meets the sky. The dominant woody plant in the area, mesquite juts out as green crowns among the drying grasses that give the grassland a hue of yellow, red and olive streaks in the winter and summer. Velavadar is home to a large population of the threatened native antelope, blackbuck (Antilope cervicapra). Male blackbuck defend territories in open grasslands; these territories are either solitary or in clusters called leks. The classical lek in Velavadar, the size of a football field, may have more than ninety rutting males during peak mating season. During this time, the lek turns into a battle field where males perform strenuous displays and engage in fierce fights to defend their territories. Females visit the lek and seem to use a variety of information to choose a male to mate with. Males use urine and dung to create huge scent marks on their territories. These dung-piles can be seen as black dots from outer space (Look at blackbuck dung-piles on Google satellite images at 22° 2’54.82″N and 72° 1’20.78″E).

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Fruit removal by male blackbuck (Antilope cervicapra) captured in a camera trap

3_Seed deposition through dung on a male mating territory- Inset- Large dung-pile on the classical lek

Seed deposition through dung on a male blackbuck mating territory. Inset: A large dung-pile on the classical lek

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Presence of mesquite seeds in blackbuck dung

As blackbuck prefer open habitats, we predict that this concentrated seed dispersal by males will result in a positive feedback process where territories, which are typically in open grasslands, are modified into woodland patches, following which  males shift their territories to more open areas. We also predict that this male-aided conversion of grasslands to mesquite woodlands will negatively affect this open plains antelope species and cause shifts in mating system and social organization and a reduction in population size. Thus, here is one mechanism of spread of a woody invasive in grasslands, where one sex of a disperser, here male blackbuck, through its extreme mating behaviour, is planting seeds in new habitat, and perhaps negatively affecting its own lifestyle.

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Seedling growing in a dung-pile on a blackbuck mating territory

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