Composition of the pollinator community, pollination and the mating system for a shrub in fragments of species rich kwongan in south-west Western Australia

Abstract

In this study we investigate the composition of the potential honeyeater pollinator community, patterns of honeyeater visitation, pollination and the mating system in a range of population fragments for the bird-pollinated mixed mating system shrub Calothamnus quadrifidus R.Br. Specifically, we aimed to answer the following questions. For smaller and more isolated population fragments are honeyeater species lost from the pollinator community, patterns of visitation different, levels of pollination lower and rates of selfing, biparental inbreeding and correlated paternity higher. The composition of the honeyeater community was similar across population fragments and there was no relationship between the abundance of birds and population fragment size. Honeyeaters were most commonly observed visiting numerous inflorescences within single plants in all populations, but as population fragments became larger movements between plants were more commonly observed. Our observations of honeyeater visitation were generally consistent with our measurements of pollination and patterns in the mating system across population fragments. We found no significant relationship between population fragment size and levels of pollination. Mating system studies showed outcrossing rates (t m ) comparable to those found in other bird-pollinated Myrtaceae, and ranged from 0.54 to 0.90 across populations. Outcrossing rates were not significantly correlated with log population size, but correlations of outcrossed paternity indicate a clear trend from low correlated paternity in larger populations to significantly higher correlated paternities in smaller populations. As a consequence mating in small populations will occur between much smaller groups of plants, and this may affect population fitness in subsequent generations.

Estimation of outcrossing rates at hierarchical levels of fruits, individuals, populations and species in Magnolia stellata

“…Plants with such systems vary widely in terms of pollination system, flowering phenology, life form and susceptibility to inbreeding depression. Furthermore, variation in outcrossing rates, caused by these factors, has been widely observed at a range of hierarchical levels, including regions (Bower and Aitken, 2007;Mable and Adam, 2007), populations (Routley et al, 1999;Bower and Aitken, 2007;Karasawa et al, 2007;Michalski and Durka, 2007;Yates et al, 2007;Ishida, 2008), individuals (El-Kassaby et al, 1993;Lee, 2000;Bower and Aitken, 2007;Nassar et al, 2007;de-Lucas et al, 2008), parts within individual plants (El-Kassaby et al, 1993;Patterson et al, 2004) and fruits (Cruzan et al, 1994). The effects of pollination systems can be illustrated by the differences between wind-pollinated and insectpollinated species.…”

Altered Soil Properties Inhibit Fruit Set but Increase Progeny Performance for a Foundation Tree in a Highly Fragmented Landscape

“…A similar effect may have occurred for insect pollinators within E. wandoo populations, as nutrient enrichment and enhanced productivity at edges appears to have led to greater species diversity and abundance of some canopy-dwelling insects in highly fragmented E. wandoo woodland remnants (Majer et al, 2000). In contrast, the bird-pollinated SWAFR endemic Calothamnus quadrifidus showed similar numbers of honeyeater visits and pollen tubes regardless of population size (Yates et al, 2007a), but experienced high rates of pollen immigration into small populations (Byrne et al, 2007). Within highly fragmented E. wandoo populations, pollen immigration has been shown to be substantial and locally-foraging insects may effect most local pollinations while birds may be responsible for most pollen immigration.…”

“…Small and isolated populations can act as stepping stones in a fragmented landscape and attract pollinator visits, leading to high rates of pollen immigration (White et al, 2002;Bacles et al, 2005;Byrne et al, 2007Byrne et al, , 2008Ottewell et al, 2009), but levels of pollination are nevertheless usually either unchanged (Yates et al, 2007a), reduced or erratic (Aizen and Feinsinger, 1994;Ottewell et al, 2009). A similar effect may have occurred for insect pollinators within E. wandoo populations, as nutrient enrichment and enhanced productivity at edges appears to have led to greater species diversity and abundance of some canopy-dwelling insects in highly fragmented E. wandoo woodland remnants (Majer et al, 2000).…”

“…According to optimal foraging theory, pollinators may concentrate their foraging effort among fewer trees as population size decreases, leading to increased within-plant foraging effort (e.g., Yates et al, 2007a). This is supported by lower withinpopulation outcrossing in several small E. wandoo populations , and by the negative relationship of effective outcrossing rates with pollen tube abundance in comparisons among maternal plants.…”

“…Despite changes in pollen quality, the level of pollination and pollinator abundance was unchanged in Calothamnus quadrifidus (Yates et al, 2007a), while honeybees have increased (González-Varo et al, 2009) or decreased (Hingston et al, 2004) pollination rates in some species of Myrtaceae. In addition, progeny performance measured as germination and seedling fitness among eucalypts is often unaffected by fragmentation (Krauss et al, 2007;Yates et al, 2007b;Breed et al, 2015; but see Burrows, 2000;Breed et al, 2012).…”