Philosophical Transactions of the Royal Society B: Biological Sciences
Fragmentation—the process by which habitats are transformed into smaller patches isolated from ea... more Fragmentation—the process by which habitats are transformed into smaller patches isolated from each other—has been identified as a major threat for biodiversity. Fragmentation has well-established demographic and population genetic consequences, eroding genetic diversity and hindering gene flow among patches. However, fragmentation should also select on life history, both predictably through increased isolation, demographic stochasticity and edge effects, and more idiosyncratically via altered biotic interactions. While species have adapted to natural fragmentation, adaptation to anthropogenic fragmentation has received little attention. In this review, we address how and whether organisms might adapt to anthropogenic fragmentation. Drawing on selected case studies and evolutionary ecology models, we show that anthropogenic fragmentation can generate selection on traits at both the patch and landscape scale, and affect the adaptive potential of populations. We suggest that dispersal...
Question: Can the reproductive benefits gained by mitigating the costs of self-pollination drive ... more Question: Can the reproductive benefits gained by mitigating the costs of self-pollination drive the evolution of nectarless flowers? Features of model: Complementary analytical and simulation models determined the optimal proportion of nectarless flowers ('nectar phenotype') to maximize male reproductive success. Models considered a range of self-pollination costs and pollinator abundances. In the analytical model, equal numbers of each nectar phenotype were present. Pollinators used simple rules of behaviour, related to their current host plant's perceived nectar status, to decide whether to stay on that plant or to move to a new plant. In the simulation model, pollinators used more sophisticated departure rules, comparing the current host plant's perceived nectar status to the population mean. Plants with different proportions of nectarless flowers competed for successful pollination over multiple seasons. Ranges of key variables: Relative cost of self-pollination...
Dispersal ability will largely determine whether species track their climatic niches during clima... more Dispersal ability will largely determine whether species track their climatic niches during climate change, a process especially important for populations at contracting (low-latitude/low-elevation) range limits that otherwise risk extinction. We investigate whether dispersal evolution at contracting range limits is facilitated by two processes that potentially enable edge populations to experience and adjust to the effects of climate deterioration before they cause extinction: a) climate-induced fitness declines toward range limits, and b) local adaptation to a shifting climate gradient. We simulate a species distributed continuously along a temperature gradient using a spatially explicit, individual-based model. We compare range-wide dispersal evolution during climate stability vs. directional climate change, with uniform fitness vs. fitness that declines toward range limits (RLs), and for a single climate genotype vs. multiple genotypes locally adapted to temperature. Dispersal d...
ABSTRACT 1.Pollination failure has been proposed to be an important determinant of plant species’... more ABSTRACT 1.Pollination failure has been proposed to be an important determinant of plant species’ range limits, if pollinator activity declines along an environmental gradient, directly limiting plant populations, or if plant populations decline along an environmental gradient and subsequently fail to attract sufficient visitation. Both mechanisms predict reduced pollinator visitation, increased pollen limitation, and decreased seed production towards range limits, and the first additionally predicts declining pollinator abundance independent of any particular plant species. However, many self-compatible species have some capacity for autonomous self-fertilization, which may buffer reproductive success from declining pollinator visitation if inbreeding depression is mild. Thus pollinator-mediated limits may also predict selection for reduced reliance on pollinators towards range limits.2.We tested these predictions towards the high-elevation limit of the self-compatible, bumble bee (Bombus) pollinated Rhinanthus minor, along two elevation transects in the Rocky Mountains of Alberta, Canada.3.Bombus abundance was highest at mid- (range-centre) and high-elevation (range limit) sites, so declining pollinator abundance is unlikely to impose high-elevation limits for bumble bee pollinated species in this area.4.Flowers per plant and per m2 declined at upper range limits, potentially rendering edge populations less attractive. However, visitation rate did not decline towards the range limit at either transect. Stigmatic pollen receipt declined with increasing elevation, but seed set did not, nor did outcross pollen supplementation increase seed set at any site.5.Investment in floral attractiveness (corolla area/ovary area) increased towards range limits, but capacity for high-quality autonomous seed set and adult inbreeding coefficients inferred from genetic markers were uniformly high, suggesting frequent self-fertilization and weak inbreeding depression throughout the range.6.Synthesis We found no evidence for pollination failure towards the upper range limit of R. minor. Moreover, unlike some species with a capacity for autogamy, autonomous selfing makes a major contribution to R. minor's mating system and demography, and likely buffers reproductive success from stochasticity in pollination. Continued investment in floral attractiveness despite high autonomous selfing suggests some evolutionary benefit to pollinator-mediated outcrossing, rather than ecological benefits via increasing seed quantity or quality. Given that >50% of angiosperms are self-compatible, the reproductive assurance provided by selfing may reduce the importance of pollination in limiting plant distributions compared to other biotic interactions.This article is protected by copyright. All rights reserved.
Most Aloe species are wholly or partly bird-pollinated, but a suite of seven Aloe species and two... more Most Aloe species are wholly or partly bird-pollinated, but a suite of seven Aloe species and two genera (Haworthia and Chortilirion) that likely belong within the Aloe clade (Asphodelaceae, subfamily Alooidea) share morphological characteristics suggestive of insect pollination. Field studies of one of these species, Aloe inconspicua, revealed that it is effectively and exclusively pollinated by insects, especially females of Amegilla fallax (Apidae) that visit its flowers for nectar and pollen. The small (7.9 mm±SD=2.0) white flowers produce a standing nectar crop of 0.097±0.10 μl, much less than that of bird-pollinated aloes. Unlike other aloes studied to date, birds did not visit A. inconspicua, and bird exclusion had no effect on fruit or seed production. Visiting individuals of A. fallax typically contacted stigmas and anthers with their heads while accessing nectar, and single visits by them and a halictid bee resulted in seed set. Recent molecular evidence suggests that insect-pollination is the ancestral state for the Alooidea. If similar floral morphology indicates similar pollination systems, shifts from insect- to bird-pollination and possibly reversions back to insect pollination have occurred repeatedly within the ALOE clade.
Many species' range limits (RL) occur across cont... more Many species' range limits (RL) occur across continuous environmental gradients without obvious barriers imposing them. Such RL are expected to reflect niche limits (NL) and thus to occur where populations cease to be self-sustaining. Transplant experiments comparing fitness within and beyond species' ranges can test this hypothesis, but interpretive power depends strongly on experimental design. We first identify often overlooked aspects of transplant design that are critical to establishing the causes of RL, especially incorporating transplant sites at, and source populations from, the range edge. We then conduct a meta-analysis of published beyond-range transplant experiments (n = 11 tests). Most tests (75%) found that performance declined beyond the range, with the strongest declines detected when the measure of performance was lifetime fitness (83%), suggesting that RL commonly involve niche constraints (declining habitat quality). However, only 46% supported range limits occurring at NL; 26% (mostly geographic RL) fell short of NL with self-sustaining transplants beyond the range, and 23% (all elevational RL) exceeded NL with range-edge populations acting as demographic sinks. These data suggest an important but divergent role for dispersal, which may commonly constrain geographic distributions while extending elevational limits. Meta-analysis results also supported the importance of biotic interactions at RL, particularly the long-held assertion of their role in causing low-elevation and equatorial limits.
Question: Can the reproductive benefits gained by mitigating the costs of self-pollination drive ... more Question: Can the reproductive benefits gained by mitigating the costs of self-pollination drive the evolution of nectarless flowers? Features of model: Complementary analytical and simulation models determined the optimal proportion of nectarless flowers ('nectar phenotype') to maximize male reproductive success. Models considered a range of self-pollination costs and pollinator abundances. In the analytical model, equal numbers of each nectar phenotype
Philosophical Transactions of the Royal Society B: Biological Sciences
Fragmentation—the process by which habitats are transformed into smaller patches isolated from ea... more Fragmentation—the process by which habitats are transformed into smaller patches isolated from each other—has been identified as a major threat for biodiversity. Fragmentation has well-established demographic and population genetic consequences, eroding genetic diversity and hindering gene flow among patches. However, fragmentation should also select on life history, both predictably through increased isolation, demographic stochasticity and edge effects, and more idiosyncratically via altered biotic interactions. While species have adapted to natural fragmentation, adaptation to anthropogenic fragmentation has received little attention. In this review, we address how and whether organisms might adapt to anthropogenic fragmentation. Drawing on selected case studies and evolutionary ecology models, we show that anthropogenic fragmentation can generate selection on traits at both the patch and landscape scale, and affect the adaptive potential of populations. We suggest that dispersal...
Question: Can the reproductive benefits gained by mitigating the costs of self-pollination drive ... more Question: Can the reproductive benefits gained by mitigating the costs of self-pollination drive the evolution of nectarless flowers? Features of model: Complementary analytical and simulation models determined the optimal proportion of nectarless flowers ('nectar phenotype') to maximize male reproductive success. Models considered a range of self-pollination costs and pollinator abundances. In the analytical model, equal numbers of each nectar phenotype were present. Pollinators used simple rules of behaviour, related to their current host plant's perceived nectar status, to decide whether to stay on that plant or to move to a new plant. In the simulation model, pollinators used more sophisticated departure rules, comparing the current host plant's perceived nectar status to the population mean. Plants with different proportions of nectarless flowers competed for successful pollination over multiple seasons. Ranges of key variables: Relative cost of self-pollination...
Dispersal ability will largely determine whether species track their climatic niches during clima... more Dispersal ability will largely determine whether species track their climatic niches during climate change, a process especially important for populations at contracting (low-latitude/low-elevation) range limits that otherwise risk extinction. We investigate whether dispersal evolution at contracting range limits is facilitated by two processes that potentially enable edge populations to experience and adjust to the effects of climate deterioration before they cause extinction: a) climate-induced fitness declines toward range limits, and b) local adaptation to a shifting climate gradient. We simulate a species distributed continuously along a temperature gradient using a spatially explicit, individual-based model. We compare range-wide dispersal evolution during climate stability vs. directional climate change, with uniform fitness vs. fitness that declines toward range limits (RLs), and for a single climate genotype vs. multiple genotypes locally adapted to temperature. Dispersal d...
ABSTRACT 1.Pollination failure has been proposed to be an important determinant of plant species’... more ABSTRACT 1.Pollination failure has been proposed to be an important determinant of plant species’ range limits, if pollinator activity declines along an environmental gradient, directly limiting plant populations, or if plant populations decline along an environmental gradient and subsequently fail to attract sufficient visitation. Both mechanisms predict reduced pollinator visitation, increased pollen limitation, and decreased seed production towards range limits, and the first additionally predicts declining pollinator abundance independent of any particular plant species. However, many self-compatible species have some capacity for autonomous self-fertilization, which may buffer reproductive success from declining pollinator visitation if inbreeding depression is mild. Thus pollinator-mediated limits may also predict selection for reduced reliance on pollinators towards range limits.2.We tested these predictions towards the high-elevation limit of the self-compatible, bumble bee (Bombus) pollinated Rhinanthus minor, along two elevation transects in the Rocky Mountains of Alberta, Canada.3.Bombus abundance was highest at mid- (range-centre) and high-elevation (range limit) sites, so declining pollinator abundance is unlikely to impose high-elevation limits for bumble bee pollinated species in this area.4.Flowers per plant and per m2 declined at upper range limits, potentially rendering edge populations less attractive. However, visitation rate did not decline towards the range limit at either transect. Stigmatic pollen receipt declined with increasing elevation, but seed set did not, nor did outcross pollen supplementation increase seed set at any site.5.Investment in floral attractiveness (corolla area/ovary area) increased towards range limits, but capacity for high-quality autonomous seed set and adult inbreeding coefficients inferred from genetic markers were uniformly high, suggesting frequent self-fertilization and weak inbreeding depression throughout the range.6.Synthesis We found no evidence for pollination failure towards the upper range limit of R. minor. Moreover, unlike some species with a capacity for autogamy, autonomous selfing makes a major contribution to R. minor's mating system and demography, and likely buffers reproductive success from stochasticity in pollination. Continued investment in floral attractiveness despite high autonomous selfing suggests some evolutionary benefit to pollinator-mediated outcrossing, rather than ecological benefits via increasing seed quantity or quality. Given that >50% of angiosperms are self-compatible, the reproductive assurance provided by selfing may reduce the importance of pollination in limiting plant distributions compared to other biotic interactions.This article is protected by copyright. All rights reserved.
Most Aloe species are wholly or partly bird-pollinated, but a suite of seven Aloe species and two... more Most Aloe species are wholly or partly bird-pollinated, but a suite of seven Aloe species and two genera (Haworthia and Chortilirion) that likely belong within the Aloe clade (Asphodelaceae, subfamily Alooidea) share morphological characteristics suggestive of insect pollination. Field studies of one of these species, Aloe inconspicua, revealed that it is effectively and exclusively pollinated by insects, especially females of Amegilla fallax (Apidae) that visit its flowers for nectar and pollen. The small (7.9 mm±SD=2.0) white flowers produce a standing nectar crop of 0.097±0.10 μl, much less than that of bird-pollinated aloes. Unlike other aloes studied to date, birds did not visit A. inconspicua, and bird exclusion had no effect on fruit or seed production. Visiting individuals of A. fallax typically contacted stigmas and anthers with their heads while accessing nectar, and single visits by them and a halictid bee resulted in seed set. Recent molecular evidence suggests that insect-pollination is the ancestral state for the Alooidea. If similar floral morphology indicates similar pollination systems, shifts from insect- to bird-pollination and possibly reversions back to insect pollination have occurred repeatedly within the ALOE clade.
Many species' range limits (RL) occur across cont... more Many species' range limits (RL) occur across continuous environmental gradients without obvious barriers imposing them. Such RL are expected to reflect niche limits (NL) and thus to occur where populations cease to be self-sustaining. Transplant experiments comparing fitness within and beyond species' ranges can test this hypothesis, but interpretive power depends strongly on experimental design. We first identify often overlooked aspects of transplant design that are critical to establishing the causes of RL, especially incorporating transplant sites at, and source populations from, the range edge. We then conduct a meta-analysis of published beyond-range transplant experiments (n = 11 tests). Most tests (75%) found that performance declined beyond the range, with the strongest declines detected when the measure of performance was lifetime fitness (83%), suggesting that RL commonly involve niche constraints (declining habitat quality). However, only 46% supported range limits occurring at NL; 26% (mostly geographic RL) fell short of NL with self-sustaining transplants beyond the range, and 23% (all elevational RL) exceeded NL with range-edge populations acting as demographic sinks. These data suggest an important but divergent role for dispersal, which may commonly constrain geographic distributions while extending elevational limits. Meta-analysis results also supported the importance of biotic interactions at RL, particularly the long-held assertion of their role in causing low-elevation and equatorial limits.
Question: Can the reproductive benefits gained by mitigating the costs of self-pollination drive ... more Question: Can the reproductive benefits gained by mitigating the costs of self-pollination drive the evolution of nectarless flowers? Features of model: Complementary analytical and simulation models determined the optimal proportion of nectarless flowers ('nectar phenotype') to maximize male reproductive success. Models considered a range of self-pollination costs and pollinator abundances. In the analytical model, equal numbers of each nectar phenotype
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