Testing the niche‐breadth–range‐size hypothesis: habitat specialization vs. performance in Australian alpine daisies

Abstract

Relatively common species within a clade are expected to perform well across a wider range of conditions than their rarer relatives, yet experimental tests of this "niche-breadth-range-size" hypothesis remain surprisingly scarce. Rarity may arise due to trade-offs between specialization and performance across a wide range of environments. Here we use common garden and reciprocal transplant experiments to test the niche-breadth-range-size hypothesis, focusing on four common and three rare endemic alpine daisies (Brachyscome spp.) from the Australian Alps. We used three experimental contexts: (1) alpine reciprocal seedling experiment, a test of seedling survival and growth in three alpine habitat types differing in environmental quality and species diversity; (2) warm environment common garden, a test of whether common daisy species have higher growth rates and phenotypic plasticity, assessed in a common garden in a warmer climate and run simultaneously with experiment 1; and (3) alpine reciprocal seed experiment, a test of seed germination capacity and viability in the same three alpine habitat types as in experiment 1. In the alpine reciprocal seedling experiment, survival of all species was highest in the open heathland habitat where overall plant diversity is high, suggesting a general, positive response to a relatively productive, low-stress environment. We found only partial support for higher survival of rare species in their habitats of origin. In the warm environment common garden, three common daisies exhibited greater growth and biomass than two rare species, but the other rare species performed as well as the common species. In the alpine reciprocal seed experiment, common daisies exhibited higher germination across most habitats, but rare species maintained a higher proportion of viable seed in all conditions, suggesting different life history strategies. These results indicate that some but not all rare, alpine endemics exhibit stress tolerance at the cost of reduced growth rates in low-stress environments compared to common species. Finally, these findings suggest the seed stage is important in the persistence of rare species, and they provide only weak support at the seedling stage for the niche-breadth-range-size hypothesis.

Range size and growth temperature influence Eucalyptus species responses to an experimental heatwave

“…Using climatically similar provenances of four Eucalyptus species, we found that species with large range sizes showed less visible heatwave damage and greater physiological tolerance of heatwave conditions than species with smaller range sizes. Other studies have observed inconsistent associations between plant species range size and environmental tolerance (Hirst, Griffin, Sexton, & Hoffmann, ; Lacher & Schwartz, ), although none have examined heatwave tolerance. Separate from species range size, other aspects of species adaptation could also influence species tolerance of heatwaves.…”

Determinants of geographic range size in plants

“…flowering time, specific leaf area) varies across environments at the genotypic level (Sexton et al , ). This may explain the lack of strong support for a positive relationship between phenotypic plasticity and range size, especially since studies differ drastically in focal traits used for quantifying plasticity (e.g., Sheth & Angert, ; Lovell & McKay, ; Hirst et al , ) and are often unable to determine whether plasticity is adaptive (Dostál et al , ).…”

Germination niche breadth varies inconsistently among three Asclepias congeners along a latitudinal gradient

“…; Hirst et al . ). In two cases, a negative correlation was identified between germination niche breadth and environmental heterogeneity, where rare species exhibit higher germinability than their common counterparts ( e.g .…”