Negative impacts of invasive plants on conservation of sensitive desert wildlife

Abstract

Abstract.Habitat disturbance from development, resource extraction, off-road vehicle use, and energy development ranks highly among threats to desert systems worldwide. In the Mojave Desert, United States, these disturbances have promoted the establishment of nonnative plants, so that native grasses and forbs are now intermixed with, or have been replaced by invasive, nonnative Mediterranean grasses. This shift in plant composition has altered food availability for Mojave Desert tortoises (Gopherus agassizii), a federally listed species. We hypothesized that this change in forage would negatively influence the physiological ecology, immune competence, and health of neonatal and yearling tortoises. To test this, we monitored the effects of diet on growth, body condition, immunological responses (measured by gene transcription), and survival for 100 captive Mojave tortoises. Tortoises were assigned to one of five diets: native forbs, native grass, invasive grass, and native forbs combined with either the native or invasive grass. Tortoises eating native forbs had better body condition and immune functions, grew more, and had higher survival rates (>95%) than tortoises consuming any other diet. At the end of the experiment, 32% of individuals fed only native grass and 37% fed only invasive grass were found dead or removed from the experiment due to poor body conditions. In contrast, all tortoises fed either the native forb or combined native forb and native grass diets survived and were in good condition. Health and body condition quickly declined for tortoises fed only the native grass (Festuca octoflora) or invasive grass (Bromus rubens) with notable loss of fat and muscle mass and increased muscular atrophy. Bromus rubens seeds were found embedded in the oral mucosa and tongue in most individuals eating that diet, which led to mucosal inflammation. Genes indicative of physiological, immune, and metabolic functions were transcribed at lower levels for individuals fed B. rubens, indicating potential greater susceptibility to disease or other health-related problems. This study highlights the negative indirect effects of invasive grasses, such as red brome, in desert ecosystems, and provides definitive evidence of a larger negative consequence to health, survival, and ultimately population recruitment for Mojave Desert tortoises than previously understood.

Precipitation quantity and timing affect native plant production and growth of a key herbivore, the desert tortoise, in the Mojave Desert

“…Greater trait plasticity is one characteristic generally thought to enhance invasion potential of species [51], so this finding is not materially surprising. The importance of native winter annuals relative to some non-natives to many desert herbivores [9,15,52] makes changes in the ratio of native to invasive plants an important consideration for evaluating the impacts of climate change on ecological communities and declining species in particular.…”

Increasing the conservation value of powerline corridors for wild bees through vegetation management: an experimental approach

“…When repeated regularly, these management techniques cause overall diminishment of the variety of floral resources, and of the complexity of habitat required for the accumulation of nesting substrates Dixon 2009). In addition, episodic mowing on transmission line easements favors invasive plants, which can sometimes be problematic for native wildlife (Drake et al 2016;Freeman et al 2014;Bezemer et al 2014). One management strategy currently being explored by transmission companies throughout the US could potentially mitigate both problems.…”

Complex immune responses and molecular reactions to pathogens and disease in a desert reptile (Gopherus agassizii)

“…RNA extractions and cDNA synthesis from blood were performed as described by Bowen et al () on each sample collected for gene transcription. PCR primers developed for G. agassizii were used to amplify 11 genes of interest and one ribosomal housekeeping gene within each sample (see Bowen et al, and Drake et al, ). Gene transcription cycle threshold values ( C T ) were measured for the housekeeping gene (18S) and the genes of interest: AHR ‐Arylhydrocarbon Receptor, ATF , CaM ‐Calmodulin, CD9 , CL ‐Cathepsin L, HSP70 ‐Heat Shock Protein 70, Lep ‐Leptin, Mx1 , MyD88 ‐Myeloid Differentiation Factor 88, SAA ‐Serum Amyloid A, and SOD ‐Superoxide dismutase from each sample in duplicate using quantitative PCR (Supporting Information Table ).…”

“…RNA extractions and cDNA synthesis from blood were performed as described by Bowen et al (2015) on each sample collected for gene transcription. PCR primers developed for G. agassizii were used to amplify 11 genes of interest and one ribosomal housekeeping gene within each sample (see Bowen et al, 2015 andDrake et al, 2016). Gene transcription cycle threshold values (C T ) were We analyzed the qPCR gene transcript data using normalized C T values.…”

“…However, given the limited understanding of immunity in reptiles (Zimmerman, Vogel, et al, ) and the additional time and resources needed to elicit an induced response (Sandmeier, Weitzman et al, ), a broader approach may be more appropriate to assess their responses to infection or other stressors. Recent studies using gene transcription profiling have advanced the evaluation of immune function in reptiles (Bowen et al, ; Drake et al, ; Krivoruchko & Storey, ) and other ectotherms (Connon et al, ). Gene transcription works by targeting specific genes that respond to intrinsic (e.g.…”