An Experimental Test of Fragmentation and Loss of Habitat With Oryzaephilus Surinamensis

Abstract

This research used a model experimental system to explore the joint effects of resource fragmentation and resource deterioration on population dynamics. The system provides a rapid test of conservation theory and can aid in planning for large and expensive studies. The investigation subjected the sawtooth grain beetle, Oryzaephilus surinamensis (L.), to five experiments in which population abundance was monitored over time. Metapopulations were created by connecting adjacent vials of flour with rubber tubes. The metapopulations were arranged in rings, and food was replenished at two‐week intervals. The experiments examined populations in (1) habitats becoming increasingly fragmented, (2) dynamically fragmenting structure with concurrent loss of resources over time, (3) static structure, dynamic resource loss and differing numbers of patches, (4) static structural arrangements with dynamic resource loss that mimic resource deterioration and destruction, and (5) static arrangements of connected fragments with an equal total amount of food in a few large patches or several small patches. Time series of stage‐specific abundances were compared in repeated‐measures ANOVA. The results show that populations respond in nonlinear ways to both the amount of food and area provided. Within a confined area, when food is plentiful, individual interaction limits population abundance. When the amount of food is reduced, population abundance becomes food dependent. Immediate increase in immature abundance was a characteristic of fragmentation while a delayed reduction of adults was characteristic of food reduction. The stage‐specific interaction at intermediate food levels shows birth and death processes that control this system, and elucidates the relationship between area and food that is integral to the dynamics of patchy populations.

Effects of habitat quality and size on extinction in experimental populations

“…By contrast, for collared pikas in alpine meadows in southwest Yukon, it was habitat quality (amount of vegetation), that most influenced extinction ( Franken & Hik 2004). Similar results have been observed in laboratory populations: extinction rate was higher in fruitfly populations in smaller habitats than in larger habitats ( Forney & Gilpin 1989), and decreased habitat quality via reduced food supply increased population extinction risk in fruitflies (Philippi et al 1987), brine shrimp (Belovsky et al 1999) and grain beetles (Bancroft & Turchin 2003).…”

A review of extinction in experimental populations

“…Using a series of experiments with grain beetles Oryzaephilus surinamensis, Bancroft & Turchin (2003) examined the influence of habitat fragmentation and decreasing food abundance: 6% of 247 populations went extinct in their experiments, all from low food treatments, suggesting that habitat quality is more important for their system than habitat size.…”

“…These include: (1) determining how demographic stochasticity scales with population size (Drake 2006); (2) development of methods for identifying the optimal timing and magnitude of introductions to maximize colonization success (Pike et al 2004); (3) the long-term relative contributions of inbreeding depression, the loss of genetic diversity, and mutation accumulation to extinction risk (Frankham 2005); (4) the relative contributions of and interactions between genetic and non-genetic processes leading to extinction (Bijlsma et al 2000;Frankham 2005); (5) the genetic impacts of habitat fragmentation (Frankham 2005); (6) factors that influence outbreeding depression (Frankham 2005); (7) effects of non-random variable environments on population growth and decline (Drake 2006); (8) the interaction between environmental variation and migration on different time scales (Drake et al 2005;Long et al 2007); (9) the interaction between demographic and environmental stochasticity (Philippi et al 1987); and (10) the interaction between multiple limiting resources for population growth (Bancroft & Turchin 2003).…”

“…Habitats with greater food supply should support larger populations and thus have lower extinction risk (Bayliss & Choquenot 2003). (Philippi et al 1987;Belovsky et al 1999;Bancroft & Turchin 2003) (Holyoak 2000*;Luckinbill 1973Luckinbill *, 1974 9. Larger habitats should support larger populations and therefore lead to lower extinction risk (Klok & De Roos 1998;Hanski 1999).…”

Asynchrony, fragmentation, and scale determine benefits of landscape heterogeneity to mobile herbivores

“…Even though we maintained equal overall population density between the different landscapes, it is likely that crowding of individuals may have occurred in the less fragmented landscapes when high quality resource pulses were added. This type of phenomenon was reported in another fragmentation study that used an experimental model system with the beetle Oryzaephilus surinamensis (L.); progressively fragmented populations with constant total amounts of food had greater beetle abundance than non-fragmented populations (Bancroft and Turchin 2003). The authors attributed this finding to herbivores in more fragmented populations experiencing a release in competition for space, such that interference between individuals decreased relative to intact populations (Bancroft and Turchin 2003).…”