Untangling interactions: do temperature and habitat fragmentation gradients simultaneously impact biotic relationships?

Abstract

Gaining insight into the impact of anthropogenic change on ecosystems requires investigation into interdependencies between multiple drivers of ecological change and multiple biotic responses. Global environmental change drivers can act simultaneously to impact the abundance and diversity of biota, but few studies have also measured the impact across trophic levels. We firstly investigated whether climate (using temperature differences across a latitudinal gradient as a surrogate) interacts with habitat fragmentation (measured according to fragment area and distance to habitat edges) to impact a New Zealand tri-trophic food chain ( plant, herbivore and natural enemy). Secondly, we examined how these interactions might differentially impact both the density and biotic processes of species at each of the three trophic levels. We found evidence to suggest that these drivers act nonadditively across trophic levels. The nature of these interactions however varied: location synergistically interacted with fragmentation measures to exacerbate the detrimental effects on consumer density; and antagonistically interacted to ameliorate the impact on plant density and on the interactions between trophic levels (herbivory and parasitoid attack rate). Our findings indicate that the ecological consequences of multiple global change drivers are strongly interactive and vary according to the trophic level studied and whether density or ecological processes are investigated.

Using a newly introduced framework to measure ecological stressor interactions

“…Interactions are still poorly understood, even though there have been many empirical studies that examine the nature of ecological interactions in the lab (Folt et al 1999; Mora et al 2007; Cramp et al 2014) and in the wild (Ross et al 2004; Christensen et al 2006). Both synergistic (Relyea 2003; Gooding et al 2009; Shears & Ross 2010; Camarero et al 2011; Griffith et al 2012; Metz et al 2013; Carnell & Keough 2014; Dávalos et al 2014; Chown et al 2015; Pringle et al 2015) and antagonistic interactions (Darling et al 2010; Bansal et al 2013; Annala et al 2014; Lakeman‐Fraser & Ewers 2014; O'Regan et al 2014; Treasure & Chown 2014; Griffiths et al 2015) have been predicted in a wide range of organisms and environments. Yet basic questions remain as follows: (1) Are most interactions synergistic, antagonistic or additive (i.e.…”

Habitat loss, predation pressure and episodic heat-shocks interact to impact arthropods and photosynthetic functioning of microecosystems

“…If so, this may have been reflected in the total abundance data in ways that were obscured once scaled to densities per unit area, which may have masked the signal of the interactive effects between treatments. Overall it is clear that the influence of microecosystem area on microarthropod abundance was crucial to understand the outcome of multi-stressor interactions for these communities [ 6 – 8 , 25 , 26 ].…”

“…Habitat loss is a common feature of land use change or land management intensification that modifies and degrades the functioning of biotic communities and processes at multiple scales [ 1 , 21 , 22 ]. Climate change is expected to interact with habitat loss to affect biota, potentially by edge effects modifying the temperature within remaining habitat patches [ 23 , 24 ] or by reducing the capacity for compensatory migration and elevating extinction likelihoods by altering population connectivity, microclimate, niche space or trophic interactions [ 1 , 7 , 25 , 26 ]. At a global scale, the negative effects of habitat loss have been shown to be exacerbated in geographical areas with the highest maximum temperatures [ 27 ], which raises the possibility of synergistic interactions between habitat loss and climate change [ 9 ] that further increase rates of biodiversity loss [ 1 , 25 ].…”

“…We, therefore, expected that greatly elevated predation pressure from the introduction of a voracious generalist predator ( Dalotia coriaria Kraatz, Staphylinidae) lacking a shared coevolutionary history with the microarthropod prey populations would interact with patch size [ 35 ] to reduce prey abundance or densities most severely in smaller ecosystem patches. H3: the negative effects of extreme heat-shocks, habitat loss and elevated top-down pressure from an introduced apex predator would interact synergistically [ 24 , 26 , 36 , 37 ] to compound the reductions in microarthropod abundance, densities and body size. …”

“…H3: the negative effects of extreme heat-shocks, habitat loss and elevated top-down pressure from an introduced apex predator would interact synergistically [ 24 , 26 , 36 , 37 ] to compound the reductions in microarthropod abundance, densities and body size.…”