I am currently running an experiment to observe how an invasion of red brome impacts the growth and success of 3 native Californian plants (Plantago insularis, Phacelia tancetifolia, Salvia columbariae) across 5 different watering regimes. These watering regimes simulate conditions from extreme drought to very wet years. The experiment utilizes a total of 300 pots with 10 replicates per treatment; 100 pots are being used for each species, with 50 of those pots containing brome and 50 lacking brome.
As the experiment progresses 4 measurements will be obtained:
- Germination Success
- Establishment by 5 weeks
- Final Census
- Total Biomass production at the conclusion of the experiment
My native versus exotic competition experiment is all set up in the greenhouse, so just waiting on germination now. Have planted additive densities of 0,3,6,9,15 and 25 natives with brome at high (10 seeds) and low (5 seeds) densities, 10 reps per treatment at ambient light versus shaded conditions for a total of 200 pots. I hung up a wooden bamboo structure to provide shade and imitate shrub presence to half of the pots, and hung it in a way that it is easy to suspend for pot censusing. Here are photos of what it all looks like.
The enemy release hypothesis (ERH) of plant invasion asserts that translocation to novel communities allows exotic plants to escape population controls imposed by natural enemies in native communities. The ERH predicts that 1) invader densities are greater in non-native communities than native communities, 2) natural enemies impose strong negative effects on invader abundance in the native range but in not the non-native range. These predictions are straightforward, but testing them involves conducting parallel vegetation surveys and enemy exclusion experiments in both the native and non-native ranges of invaders. Due to logistic challenges, very few studies have done this.
As part of an international team of collaborators from the USA, Canada, and Poland, we are explicitly testing the predictions above with respect to the prickly cucumber, Echinocystis lobata (fruit pictured below). This climbing vine is native to North America but invasive in Poland, where it can dominate local communities and extirpate native competitors.
So far, our surveys indicate that E. lobata is much more abundant in Poland than anywhere examined in N. America, and that E. lobata plants are larger and more fecund in Poland than in N. America. It also seems that physical defenses aimed at protecting seeds from generalist granivores are present at much higher frequencies in Poland than in N. America, which is very cool! We look forward to results from enemy exclusion experiments.
We’ll keep you posted!
Big ears with big veins are great for thermoregulation on a 37°C day on the Carrizo Plains.
Doing behavioral observations means you can spend some serious time doing lizard glamour shots.
Kit foxes caught playing on camera traps at Carrizo Plain National Monument.
Photo courtesy of Jacob Lucero
Code, data, and exploration on GitHub.
Do native species density trials at two scale – micro and mesoscale using pots and large plastic buckets. Mix of potting soil and sand best – 50:50.
Consider intra and interspecific competition series – with replacement, i.e. keep net densities per pot consistent. Finally, perhaps consider competition with an exotic such as red brome.
with and without shade mimic in greenhouse
umbrella over buckets in mesocosm experiment
natives against brome in density series
then a*b, a*c, b*c
Or run each out in solo then against red brome.
a vs rb
b vs rb
c vs rb
at 1,2, 5, 10, 25 seeds etc or a simple with-replacement density series.
THEN, ready for it…. red brome from cali and red brome from Israel
a+b vs rb