DOI: 10.5068/d14671
title: Data from: Environmental context shapes the long‐term role of nutrients in driving producer community trajectories in a top‐down dominated marine ecosystem

description: 1. Two predominant anthropogenic impacts on ecosystems, nutrient
 enrichment and the removal of consumers, are predicted to interact in
 their effects on producer diversity. Yet, measures of diversity alone may
 not capture changes occurring in the underlying mechanisms structuring
 communities. Furthermore, evidence for these interactions in rocky
 intertidal systems is mixed and may be confounded by variable baseline
 productivity or short experimental durations that do not capture
 seasonality, environmental heterogeneity or successional
 processes.  2. We conducted a 2-year experiment examining the
 main and interactive effects of nutrients and herbivores in a
 low-productivity environment on the northern shore of Cook Strait near
 Wellington, New Zealand. We explicitly accounted for the small-scale
 spatial environmental heterogeneity characteristic of rocky
 shores.  3. Rapid and dramatic shifts in diversity metrics and
 cover of algal communities in the first year were driven by removal of
 herbivores. Within two months of herbivore exclusion, open space decreased
 from &gt; 90% to &lt; 15%, regardless of nutrient addition, and
 both algal diversity and evenness plummeted while species richness
 rose.  4. In contrast to theoretical predictions, strong
 interactions between top-down and bottom-up forces on diversity were rare;
 rather, over time, the addition of nutrients negatively impacted
 diversity. Further, where herbivores were removed, nutrients inhibited
 succession beyond ephemeral forms, contrasting with the tolerance model of
 succession observed under ambient nutrients.  5. The effects of
 nutrients were only elucidated by accounting for variation in habitat
 complexity and seasonality, demonstrating that environmental heterogeneity
 can mask bottom-up processes. Moreover, shifts in relative species
 abundances revealed that after 10 months, nutrient addition caused
 increased community turnover regardless of herbivore presence or absence,
 indicating reduced stability not apparent in simple measures of
 diversity.  6. Synthesis. Our results suggest that
 nutrient addition and herbivore reduction exert strong but mostly
 independent control on community biodiversity, where context dependency in
 habitat complexity, seasonality, and successional stage played key roles
 in determining community outcomes. These findings demonstrate the
 importance of longer-term field studies incorporating environmental
 context and multiple metrics of diversity to reveal the mechanisms
 underlying effects of nutrient enrichment and herbivore loss on producer
 community structure.
description: <strong>Clausing_readme</strong>
 Read me file with abbreviations and explanations for all data
 files.  
 Clausing_metadata This file provides
 treatment information and measures of environmental parameters for all
 experimental plots.  
 Clausing_algal_count_data This file
 represents the raw algal community data from experimental plots using the
 point-intercept surveys. Experimental treatments of nutrient enrichment
 and herbivore removal were established at the beginning of March 2010 at
 which time algal surveys were conducted (t0). Surveys were conducted
 monthly for the first 4 months and quarterly thereafter for the two-year
 experimental period.   
 Clausing_herbivore_data This file contains
 the raw herbivore survey data from experimental plots. Experimental
 treatments of nutrient enrichment and herbivore removal were established
 at the beginning of March 2010 at which time herbivores were
 surveyed (time 0) and then  densities were manipulated. Subsequent surveys
 were conducted monthly for the first 4 months and quarterly thereafter for
 the two-year experimental period.