Is dispersal easier than pollination? Two tests in New Zealand Loranthaceae

Abstract

We tested the relative frequency of pollen limitation and dispersal limitation for two birdpollinated and bird-dispersed New Zealand mistletoes, Peraxilla tetrapetala and Alepis flavida, at a South Island site where the bellbird (Anthornis melanura) is the sole pollinator and disperser. There was no evidence of dispersal limitation for P. tetrapetala over four seasons or A. flavida over two seasons. Few ripe fruits were present on plants at any one time (usually <5%), and more than 90% of the fruit crop was removed. A. flavida was not pollen limited, but P. tetrapetala was significantly pollen limited in 6 of 10 years. The presence of pollen limitation but not dispersal limitation, despite both services depending on the same bird, is influenced by the much faster rates of flower ripening per day compared with fruit ripening (15-54 times faster in P. tetrapetala). In New Zealand, pollination failure probably threatens at least as many plant species as dispersal failure. In theory, dispersal should threaten fewer plant species, because dispersal usually involves more animal species, makes smaller quantitative demands on the dispersers (fewer fruits B02086; ripening per day, and fruits can wait longer for attention), and may be less obligate for at least some reproduction to occur.

Frugivore loss limits recruitment of large-seeded trees

“…The weighted mean survival was then expressed relative to the best-case scenario (100% of fruits consumed, no mammals). Although it is unlikely that fruit consumption by frugivores would reach 100 per cent in the wild, two multi-year studies in New Zealand mistletoes [6] came close (means approx. 95% consumption) and the model results would be very little changed (approx.…”

“…The effectiveness of animal seed dispersers depends on both the quantity (number of seeds dispersed) and quality (seed treatment after ingestion and quality of deposition sites) of dispersal [5]. There are a number of possible mechanisms by which plant recruitment could be affected if dispersers decline, but their strength and frequency is often unclear [6,7]. Recent observational studies report lower seedling densities in forests with fewer frugivores [8], but these may be affected by confounding factors.…”

Assessing pollination and fruit dispersal inFuchsia excorticata(Onagraceae)

“…This is particularly relevant to New Zealand (Craig et al 2000) as many terrestrial bird species are extinct (Holdaway 1989) or declining (Hitchmough et al 2007), putting at risk pollination and dispersal services (Clout & Hay 1989;Craig et al 2000;Newstrom & Robertson 2005). Significant disruptions to bird-plant mutualisms have been recently demonstrated in New Zealand forest species, and it appears that m any birdvisited plants now suffer from incomplete pollination and/or fruit dispersal (McNutt 1998;Robertson et al 1999;Montgomery et al 2001;Kelly et al 2004;Merrett et al 2007).…”

Relative (Un)Importance of Introduced Animals as Pollinators and Dispersers of Native Plants

“…The fruit and seed production for six of seven species of bird-pollinated trees and shrubs has been shown to be pollen-limited at some mainland sites (Anderson et al 2006). For instance, the red mistletoe (Peraxilla tetrapetala) is regularly pollen-limited at two South Island sites Kelly et al 2004), and the climbing fuchsia (Fuchsia perscandens) also has very low fruit set at two sites near .…”