N-P Co-Limitation of Primary Production and Response of Arthropods to N and P in Early Primary Succession on Mount St. Helens Volcano

Abstract

BackgroundThe effect of low nutrient availability on plant-consumer interactions during early succession is poorly understood. The low productivity and complexity of primary successional communities are expected to limit diversity and abundance of arthropods, but few studies have examined arthropod responses to enhanced nutrient supply in this context. We investigated the effects of nitrogen (N) and phosphorus (P) addition on plant productivity and arthropod abundance on 24-yr-old soils at Mount St. Helens volcano.Methodology/Principal FindingsWe measured the relative abundance of eight arthropod orders and five families in plots that received N, P, or no nutrients for 3–5 years. We also measured plant % cover, leaf %N, and plant diversity. Vegetation responded rapidly to N addition but showed a lagged response to P that, combined with evidence of increased N fixation, suggested P-limitation to N availability. After 3 yrs of fertilization, orthopterans (primarily Anabrus simplex (Tettigoniidae) and Melanoplus spp (Acrididae)) showed a striking attraction to P addition plots, while no other taxa responded to fertilization. After 5 yrs of fertilization, orthopteran density in the same plots increased 80%–130% with P addition and 40% with N. Using structural equation modeling, we show that in year 3 orthopteran abundance was associated with a P-mediated increase in plant cover (or correlated increases in resource quality), whereas in year 5 orthopteran density was not related to cover, diversity or plant %N, but rather to unmeasured effects of P, such as its influence on other aspects of resource quality.Conclusions/SignificanceThe marked surprising response to P by orthopterans, combined with a previous observation of P-limitation in lepidopteran herbivores at these sites, suggests that P-mediated effects of food quantity or quality are critical to insect herbivores in this N-P co-limited primary successional system. Our results also support a previous suggestion that the availability of N in these soils is P-limited.

Herbivore and pollinator responses to grassland management intensity along experimental changes in plant species richness

“…Here, high management intensity positively affected the number of grasshopper individuals, supporting published findings (Drummond et al, 2008;Bishop et al, 2010), whereas other studies showed a decrease of grasshopper individuals in fertilization treatments mediated by changes in the vegetation structure (Wingerden et al, 1992;Marini et al, 2008). Vegetation structure is an important parameter for grasshoppers in large-scale habitats (Morris, 2000), but is of minor importance for experiments at smaller scales (such as ours), where patches of different vegetation structure are in close vicinity.…”

Not just the usual suspects: Insect herbivore populations and communities are associated with multiple plant nutrients

“…Apple et al (2009) found that naturally occurring foliar P levels were positively correlated with caterpillar survival and growth rate at an early primary succession terrestrial habitat. At this same site, Bishop et al (2010) also documented that P addition promoted orthopteran abundance (primarily Melanoplus spp.…”

Dietary phosphate affects food selection, post-ingestive P fate, and performance of a polyphagous herbivore

“…This contention is supported by experimental tests of plant nutrient limitation (Bishop et al, 2010;Elser et al, 2007) and correlations between host plant P content and grasshopper abundance (Joern et al, 2012). Indeed, P levels in terrestrial foliage range widely.…”

“…However, Joern et al (2012) found that plant P content was the most important element predicting overall grasshopper abundance in the central Nebraskan grasslands. Moreover, fertilization of natural plants with P directly stimulates growth and population density of a variety of insects, including Orthopterans on Mount St Helens volcano (Bishop et al, 2010). For monophagous or limited-mobility insects, limitations by dietary P may be more likely and prevalent (Apple et al, 2009;Perkins et al, 2004).…”