Pollination

History of deer colonization - Response of vegetation to deer - Response of animals to deer and squirrel - Deer biology

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Effect of browsing history on the vegetation - Effect of chemical defences on deer browsing - Effects of reduced plant abundance on pollination - Effect of hunting on tree regeneration - Effect of prolonged deer population reduction on the vegetation

Effect of reducted plant abundance on pollination

Aim & scope - Where & when - How - Main results and conclusions - Scientific Publications

Aim and scope

We investigated whether a reduced abundance of flowering plants on islands with a long history of deer browsing (Effects of different browsing histories) together with a lower abundance of pollinators on these islands (Response of invertebrates to deer browsing) did affect the effectiveness of pollination.

We compared pollination of Red columbine (Aquilegia formosa) between islands without deer and islands with deer for over 50 years.

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Where and when

Diego Vasquez and collaborators conducted pollination experiments in 2005 on 6 islands of Laskeek Bay:

3 islands had no deer (Low, South Low, Lost)
3 had been colonised by deer for more than 50 years (East Limestone, West Limestone, Haswell)

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How

Reproductive success (seed production) was compared between islands with and without deer.

Comparison of pollination and reproductive success
between islands with and without deer

Pollination success was evaluated by quantifying:

the proportion of grains of red columbine pollen deposited on flower stigmas, relatively to grains of pollen from other species.
the number of grains of pollen that grew a pollen tube in the pistils

Reproductive success was quantified by:

the number of flowers per plant
the number of fruits per plant and per flower
the number of seeds per fruit, per flower and per plant

Reproductive success can be affected by pollen availability or resource availability.

Pollination can be pollinator-mediated pollination or self-pollination (the stigma of a flower is pollinated by pollen falling from the etamines of the same flower).

Up to which extent does
pollen availability determine reproductive success ?

	Pairs of plants were randomly chosen along shoreline transects on the different islands. Each pair consisted of: a hand-pollinated plant (pollen was artificially added on stigmas) a naturally pollinated plant (untouched)
If pollen availability determines reproductive success, a reduction in the number of pollen grains deposited should lead to a lower reproductive success. Thus increasing pollen load by hand pollination should lead to higher reproductive success.

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Main Results and conclusions

On deer-colonised islands, the density of Red columbine is drastically lower, but its density relatively to other wildflower species is higher.

Red columbine pollen concentration on stigmas is higher on islands with deer than on islands without, probably because red columbine is the main flowering plant that remains available to the few pollinators present.

Reproductive success is similar on all islands.

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Scientific Publications

Diego P. Vazquez, Julie Gresser, Jean-Louis Martin, 2010, Introduced deer and the pollination and reproduction of an animal-pollinated herb, Botany 88: 110–118 (2010) - PDF

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