Dave Kelly

The evolutionary ecology of mast seeding

The past seven years have seen a revolution in understanding the causes of mast seeding In perennial plants. Before 1987, the two main theories were resource matching (i.e. plants vary their reproductive output to match variable resources) and predator satiation (i.e. losses to predators are reduced by varying the seed crop). Today, resource matching is restricted to a proximate role, and predator satiation is only one of many theories for the ultimate advantage of masting. Wind pollination, prediction of favourable years for seedling establishment, animal pollination, animal dispersal of fruits, high accessory costs of reproduction and large seed size have all been advanced as possible causes of masting. Of these, wind pollination, predator satiation and environmental prediction are important in a number of species, but the other theories have less support. In future, Important advances seem likely from quantifying synchrony within a population, and examining species with very constant reproduction between years.

ESTIMATING BIOCONTROL AGENT IMPACT WITH MATRIX MODELS: CARDUUS NUTANS IN NEW ZEALAND

We demonstrate the use of matrix models to assess the impact of biological control and other pest management strategies with a case study of Carduus nutans (nodding thistle) in New Zealand. Modeling can facilitate the choice of the best control agents, improve evaluation of biocontrol attempts, and assist in the design of integrated pest management plans. Field data for ∼8000 mapped C. nutans plants at two sites in New Zealand were used to develop size-structured matrix models. The matrix models confirm that both populations of C. nutans were increasing in number, as is expected of a noxious weed in its invasion phase. Elasticity analysis indicated that seed/seedling and small-plant/seed transitions were more crucial to population growth than rosette survival rates. However, simulations of attack by the biocontrol agent Rhinocyllus conicus (nodding thistle receptacle weevil) showed that seed losses of ∼69% would be required to make the populations decrease in size, far more than the observed losses of 30–...

MASTING BY EIGHTEEN NEW ZEALAND PLANT SPECIES: THE ROLE OF TEMPERATURE AS A SYNCHRONIZING CUE

Masting, the intermittent production of large flower or seed crops by a population of perennial plants, can enhance the reproductive success of participating plants and drive fluctuations in seed-consumer populations and other ecosystem components over large geographic areas. The spatial and taxonomic extent over which masting is synchronized can determine its success in enhancing individual plant fitness as well as its ecosystem-level effects, and it can indicate the types of proximal cues that enable reproductive synchrony. Here, we demonstrate high intra- and intergeneric synchrony in mast seeding by 17 species of New Zealand plants from four families across >150 000 km2. The synchronous species vary ecologically (pollination and dispersal modes) and are geographically widely separated, so intergeneric synchrony seems unlikely to be adaptive per se. Synchronous fruiting by these species was associated with anomalously high temperatures the summer before seedfall, a cue linked with the La Nina phase of ...

QUANTIFYING THE IMPACT OF COMPETITION AND SPATIAL HETEROGENEITY ON THE STRUCTURE AND DYNAMICS OF A FOUR-SPECIES GUILD OF WINTER ANNUALS

We develop statistical methods appropriate for the analysis of spatially structured population data. The methods are used to study the structure and dynamics of a four-species annual plant guild recorded in 1,000 permanent squares over a 10-yr period. We parameterize models that predict population density from one year to the next. In agreement with theoretical expectation all the models have locally stable equilibria, and overcompensation is rare. We demonstrate that interspecific interactions are extremely weak, relative to intraspecific ones, and that the spatial arrangement of species and individuals within them is critical to the observed dynamics. The impact of spatial density-dependent population growth on observed densities was calculated. In 52% of the cases population size would have been increased by at least a factor of 1.5 had there been no interactions between individuals, and in 9% of these it would have increased by a factor of four or more. This effect is shown to be largely a result of intraspecific interactions. We discuss possible explanations for the weakness of interspecific interactions.

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.

The Need to Quantify Ecosystem Services Provided By Birds

— 1 — The Auk, Vol. 128, Number 1, pages 1−14. ISSN 0004-8038, electronic ISSN 1938-4254.  2011 by The American Ornithologists’ Union. All rights reserved. Please direct all requests for permission to photocopy or reproduce article content through the University of California Press’s Rights and Permissions website, http://www.ucpressjournals. com/reprintInfo.asp. DOI: 10.1525/auk.2011.10248 8Present address: Loras College, 1450 Alta Vista, Dubuque, Iowa 52004, USA. E-mail: harrier2@mchsi.com 9Present address: Department of Biology, University of Utah, 257 South 1400 East, Room 201, Salt Lake City, Utah 84112, USA. The Auk 128(1):1–14, 2011  The American Ornithologists’ Union, 2011. Printed in USA. The Auk An International Journal of Ornithology

The reproductive biology of the New Zealand flora

New Zealands long isolation from other elements of Gondwanaland, oceanic climate, the unusual combination of ancient Gondwanic, tropical and more recently arrived elements in its flora, and its relatively depauperate pollinator and disperser fauna have set the stage for the evolution of a subtle, complex and distinctive reproductive biology. This contrasts markedly with the neighbouring continent of Australia where the fauna is diverse and the flowers vivid. Recent advances in understanding New Zealands floral biology include evidence that the ancestor to the anthophytes was cosexual, with insect pollinators receiving stigmatic nectar rewards; the discovery of ground-level bat pollination in an obligate root parasite; the finding that the greater resource sensitivity of fruit set in males than in females may account for sex ratio variation in gynodioecious species; and, evidence for much more pronounced mast seeding at higher altitudes even in the absence of mammalian seed predators.

Evaluating the wind pollination benefits of mast seeding

We developed a conceptual model for evaluating the benefits of wind pollination to mast-flowering species. The benefit that a plant population gains from mast flowering via increased wind pollination efficiency was predicted from how far pollination efficiency at mean seed crop size falls below the maximum. Species were most likely to benefit from mast seeding if mean reproductive effort in the field gave an intermediate level of pollination efficiency, regardless of the cost of unpollinated female structures. To quantify the benefits of different degrees of mast flowering, a simulation model was used to alter the seed production coefficient of variation (cv) and to calculate its effects on weighted mean pollination efficiency. The model was applied to seven real data sets for five species with pollination benefits from masting that ranged from relatively small (Chionochloa pallens), to moderate (Dacrydium cupressinum, Betula alleghaniensis), to large (Nothofagus solandri, N. menziesii). Many studies have reported higher seed production coefficients of variation at higher altitudes and latitudes within a species. Our model showed that higher coefficients of variation are favored by reduced mean seed output per plant at higher altitudes. Data for N. solandri at three altitudes in one site showed much higher pollination benefits from masting at higher altitudes. Reduced plant density (e.g., through fragmentation), which also lowers mean flowering effort per unit area, resulted in large increases in masting benefits in N. solandri, but only small increases in C. pallens. These contrasting results were primarily due to differences between the two species in mean reproductive effort vs. wind pollination efficiency, rather than to differences in the effects of fragmentation and altitude. The relative effects of masting on pollination, insect seed predation, and bird seed predation were modeled in B. alleghaniensis. Masting produced a small economy of scale from insect predator satiation, but an almost equivalent diseconomy of scale resulted from increased levels of bird seed predation. Efficiency of wind pollination improved moderately with increasing cv, providing some overall benefits from masting in this species. Accordingly, we propose that masting can be favored by either one dominant economy of scale (such as wind pollination efficiency in N. solandri or predator satiation in C. pallens), or a balance among several factors (such as pollination, predator satiation, and predator attraction in B. alleghaniensis). We predict that, in the absence of any selective benefits or disadvantages of masting, plants would be expected to have coefficients of variation in the range 0.85–1.35.

CONTEXT-DEPENDENT BIOLOGICAL CONTROL OF AN INVASIVE THISTLE

Carduus nutans (nodding or musk thistle) is an important invasive plant of Eurasian origin. Biological control of this species, using insects that attack rosettes or developing seed heads, has met with varied success in different parts of its invaded range. Here we develop and compare simple demographic matrix models for populations of this species in Australia and New Zealand, to explore reasons for these differences. In a New Zealand population, rapid population growth of C. nutans is driven by early life history transitions. In an Australian population, fecundity of C. nutans is of reduced importance, and survivorship of rosettes plays an increased role. These differences suggest how biocontrol agents that are successful at providing control in one situation may fail in another. Theoretical explorations of the models show which life history transitions drive the differences in matrix elasticities. We suggest that characteristics of the invaded community also play a role in invasion success of this spec...

Snow Tussocks, Chaos, and the Evolution of Mast Seeding

One hitherto intractable problem in studying mast seeding (synchronous intermittent heavy flowering by a population of perennial plants) is determining the relative roles of weather, plant reserves, and evolutionary selective pressures such as predator satiation. We parameterize a mechanistic resource‐based model for mast seeding in Chionochloa pallens (Poaceae) using a long‐term individually structured data set. Each plant’s energy reserves were reconstructed using annual inputs (growing degree days), outputs (flowering), and a novel regression technique. This allowed the estimation of the parameters that control internal plant resource dynamics, and thereby allowed different models for masting to be tested against each other. Models based only on plant size, season degree days, and/or climatic cues (warm January temperatures) fail to reproduce the pattern of autocovariation in individual flowering and the high levels of flowering synchrony seen in the field. This shows that resource‐matching or simple cue‐based models cannot account for this example of mast seeding. In contrast, the resource‐based model pulsed by a simple climate cue accurately describes both individual‐level and population‐level aspects of the data. The fitted resource‐based model, in the absence of environmental forcing, has chaotic (but often statistically periodic) dynamics. Environmental forcing synchronizes individual reproduction, and the models predict highly variable seed production in close agreement with the data. An evolutionary model shows that the chaotic internal resource dynamics, as predicted by the fitted model, is selectively advantageous provided that adult mortality is low and seeds survive for more than 1 yr, both of which are true for C. pallens. Highly variable masting and chaotic dynamics appear to be advantageous in this case because they reduce seed losses to specialist seed predators, while balancing the costs of missed reproductive events.