Jenny J. Ladley

Cascading effects of bird functional extinction reduce pollination and plant density

Loss of pollinator services is reducing the population density of a New Zealand shrub. Reductions in bird numbers could hamper ecosystem services such as pollination, but experimental proof is lacking. We show that functional extinction of bird pollinators has reduced pollination, seed production, and plant density in the shrub Rhabdothamnus solandri (Gesneriaceae) on the North Island (“mainland”) of New Zealand but not on three nearby island bird sanctuaries where birds remain abundant. Pollen limitation of fruit set is strong [pollen limitation index (PLI) = 0.69] and significant on the mainland but small (PLI = 0.15) and nonsignificant on islands. Seed production per flower on the mainland is reduced 84%. Mainland sites have similar adult densities, but 55% fewer juvenile plants per adult, than island sites. Seed addition experiments near adult R. solandri plants on the mainland found strong seed limitation 5 years after sowing for R. solandri but not for two other co-occurring woody species. This demonstrates a terrestrial trophic cascade.

Warming, CO2, and nitrogen deposition interactively affect a plant‐pollinator mutualism

Environmental changes threaten plant-pollinator mutualisms and their critical ecosystem service. Drivers such as land use, invasions and climate change can affect pollinator diversity or species encounter rates. However, nitrogen deposition, climate warming and CO(2) enrichment could interact to disrupt this crucial mutualism by altering plant chemistry in ways that alter floral attractiveness or even nutritional rewards for pollinators. Using a pumpkin model system, we show that these drivers non-additively affect flower morphology, phenology, flower sex ratios and nectar chemistry (sugar and amino acids), thereby altering the attractiveness of nectar to bumble bee pollinators and reducing worker longevity. Alarmingly, bees were attracted to, and consumed more, nectar from a treatment that reduced their survival by 22%. Thus, three of the five major drivers of global environmental change have previously unknown interactive effects on plant-pollinator mutualisms that could not be predicted from studies of individual drivers in isolation.

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 bird‐pollinated 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 ripening per day, and fruits can wait longer for attention), and may be less obligate for at least some reproduction to occur.

Explosive flowering, nectar production, breeding systems, and pollinators of New Zealand mistletoes (Loranthaceae)

The six New Zealand loranthaceous mis- tletoes fall into two groups based on pollination bi- ology. Four (Alepis flavida, Peraxilla colensoi, P. tetrapetala, and Trilepidea adamsii) are bird polli- nated with hermaphrodite flowers while the other two (Ileostylus micranthus and Tupeia antarctica) are dioecious or sub-dioecious and insect pollinated. We provide data on the pollination biology of the five extant species (Trilepidea is extinct). The two Peraxilla species and Trilepidea have recently been shown to have explosive flowers. Here we show that Alepis has weakly facultatively explo- sive flowers. The world distribution of explosive mistletoe flowers suggests that the syndrome has arisen a number of times independently within the family, and is found in about half the putatively ancestral genera. The principal avian visitors to the bird-pollinated species were tui and bellbirds; introduced species are numerically unimportant as pollinators. The nectar production schedules of Alepis and Peraxilla encour- age single-visit pollination as little nectar is produced after the flowers open. However, when bird densi- ties are high, buds of Peraxilla may be forced open prematurely, encouraging multiple visits.

Distribution and population structure of the loranthaceous mistletoes Alepis flavida, Peraxilla colensoi, and Peraxilla tetrapetala within two New Zealand Nothofagus forests

Abstract Our results confirm the findings of an earlier study that suggested niche partitioning in the way Alepis flavida and Peraxilla tetrapetala utilise the available resources within the Nothofagus solandri canopy; Alepis flavida is almost exclusively an outer branch parasite while Peraxilla tetrapetala occurs most often on inner branches and the host trunk. Peraxilla colensoi has a similar distribution within host trees to Peraxilla tetrapetala, except that it parasitises Nothofagus menziesii. All three mistletoes showed non-random distribution patterns in terms of the host trees they parasitise, being found more often on larger trees. Larger host trees also carry a greater volume of mistletoe than do smaller host trees. For Alepis flavida and Peraxilla tetrapetala we found no evidence of host exclusion, whereby the presence of one mistletoe excludes the other mistletoe species establishing, observing the converse where host trees were more likely to have both mistletoe species present than expected....

Pollinator behaviour, not increased resources, boosts seed set on forest edges in a New Zealand Loranthaceous mistletoe

Abstract The endemic New Zealand mistletoe Peraxilla tetrapetala (Loranthaceae) has previously been shown to be pollinator limited, and to experience higher fruit set in increasingly fragmented habitats, but the mechanism for higher fruit set on edges has not been studied. Edges could affect plant resources (through higher light) and/or pollinator behaviour. This study measures the degree to which pollination and resource limitation affect female reproductive success along a gradient of increasing exposure to the forest edge. Forty‐two plants in pairs at varying distances from the forest edge were selected from within two Nothofagus forest fragments in the 1999/2000 season; and on one plant in each pair, all ripe undamaged flowers were hand‐pollinated. Light levels and the degree of edge exposure were measured for each plant, and path analysis was used to determine the relationship of these variables to proportion fruit set. In agreement with previous studies, unmanipulated plants were found to be strongly pollen limited, especially in shady locations. However, on plants receiving hand‐pollination, fruit set was uniformly high and was unaffected by edge exposure or light levels. Direct observation of flower visitation rates by birds in the 2000/01 season showed that edge flowers were visited twice as often as interior flowers. These results show that the higher fruit set on edges is due to visitation patterns of pollinators, and not due to greater resource availability on edges. This improved pollination on edges may help to buffer this declining plant against local extinction.

Futile Selfing in the Trees Fuchsia excorticata (Onagraceae) and Sophora microphylla (Fabaceae): Inbreeding Depression over 11 Years

Mixed mating (producing a mix of selfed and outcrossed seed) is common in flowering plants and is ecologically important because it potentially offers reproductive assurance against pollination failure. However, selfed seed offers no reproductive assurance unless it overcomes inbreeding depression. In trees and other long-lived plants, genetic evidence suggests that selfed seed seldom matures to adulthood, presumably because of severe inbreeding depression. We measured inbreeding depression over 11 yr in two populations each of two New Zealand trees, Fuchsia excorticata and Sophora microphylla, from pollination to germination and performance in both pots and the field. The accumulated inbreeding depression was very high in both cases (F. excorticata: and 0.84; S. microphylla: and 0.99) and largely late acting, especially in F. excorticata. Fewer than 10% (and <1% in three of the four cases) of the selfs remain; none have yet flowered, and they appear unlikely to do so. Hence, selfing is likely futile in these species. Thus, fruit, seed, and seedling production are not reliable indicators of successful recruitment: a high density of doomed selfed offspring can mask the absence of the outcrossed seedlings needed for adult replacement.

Establishment and early growth of Alepis flavida in relation to Nothofagus solandri branch size

Hand planted seeds of the mistleto e Alepis flavida establish much better on smal l Nothofagus solandri branches (<5 mm diameter : 48.4% establishment after one year) than on larg e branches (20-30 mm : 6.1%), whereas intermediate sized branches have intermediate establishment rate s (10 mm: 21.6%). Wild 1-4-year-old Alepis flavida seedlings occurred on branches 0.5-6 mm diameter (mean = 1 .9 mm) . There was no significant differ- ence in original branch size between tagged mistle- toe seedlings that died and those that lived, but Alepis flavida shoot extension was positively correlate d with host branch diameter increment . These dat a suggest the early establishment and survival o f Alepis flavidaseedlings is strongly dependent on th e size and vigour of the branch on which the seed has been deposited .

Circular replication-associated protein encoding DNA viruses identified in the faecal matter of various animals in New Zealand.

In recent years, innovations in molecular techniques and sequencing technologies have resulted in a rapid expansion in the number of known viral sequences, in particular those with circular replication-associated protein (Rep)-encoding single-stranded (CRESS) DNA genomes. CRESS DNA viruses are present in the virome of many ecosystems and are known to infect a wide range of organisms. A large number of the recently identified CRESS DNA viruses cannot be classified into any known viral families, indicating that the current view of CRESS DNA viral sequence space is greatly underestimated. Animal faecal matter has proven to be a particularly useful source for sampling CRESS DNA viruses in an ecosystem, as it is cost-effective and non-invasive. In this study a viral metagenomic approach was used to explore the diversity of CRESS DNA viruses present in the faeces of domesticated and wild animals in New Zealand. Thirty-eight complete CRESS DNA viral genomes and two circular molecules (that may be defective molecules or single components of multicomponent genomes) were identified from forty-nine individual animal faecal samples. Based on shared genome organisations and sequence similarities, eighteen of the isolates were classified as gemycircularviruses and twelve isolates were classified as smacoviruses. The remaining eight isolates lack significant sequence similarity with any members of known CRESS DNA virus groups. This research adds significantly to our knowledge of CRESS DNA viral diversity in New Zealand, emphasising the prevalence of CRESS DNA viruses in nature, and reinforcing the suggestion that a large proportion of CRESS DNA viruses are yet to be identified.

Pollinator limitation of seed set in Fuchsia perscandens (Onagraceae) on Banks Peninsula, South Island, New Zealand

Abstract Fuchsia perscandens, which has ornithophilous flowers, may be prone to pollinator limitation on the New Zealand mainland where pollinating birds are often scarce. To investigate this possibility, we hand pollinated flowers on plants at two sites on Banks Peninsula and compared their reproductive success with unmanipulated flowers on the same plants. In the 1999 season at Buckleys Bay, fruit initiation was 3.3 times higher on hand‐pollinated flowers (66.6% of flowers) than unmanipulated flowers (20.0%), and fruit set was 2.7 times higher (47.9% versus 18.0%, respectively). In developed fruit, seed set per fruit was higher for hand‐pollinated (70.9% of ovules) than unmanipulated flowers (48.0%). The results indicate that 34% of ovules from hand‐pollinated flowers, but 9% of ovules from unmanipulated flowers, set seed. Germination rates did not vary significantly among treatments. In the 2000 season, at both sites, fruit set of hand‐pollinated flowers was at least 1.7 times higher than unmanipulated flowers (P = 0.028), and fruit set of unmanipulated flowers did not differ significantly from that of bagged flowers from which all pollinators were excluded (P = 0.98). These results agree with other studies of ornithophilous plants on the New Zealand mainland and suggest that pollinator limitation is a frequent consequence of the rarity of honeyeater birds.